2306.00107

# MERT: Acoustic Music Understanding Model with Large-Scale Self-supervised Training > The authors contributed equally to this work. Corresponding authors. ## Abstract Self-supervised learning (SSL) has recently emerged as a promising paradigm for training generalisable models on large-scale data in the fields of vision, text, and speech. Although SSL has been proven effective in speech and audio, its application to music audio has yet to be thoroughly explored. This is partially due to the distinctive challenges associated with modelling musical knowledge, particularly tonal and pitched characteristics of music. To address this research gap, we propose an acoustic M usic und ER standing model with large-scale self-supervised T raining (MERT), which incorporates teacher models to provide pseudo labels in the masked language modelling (MLM) style acoustic pre-training. In our exploration, we identified an effective combination of teacher models, which outperforms conventional speech and audio approaches in terms of performance. This combination includes an acoustic teacher based on Residual Vector Quantisation - Variational AutoEncoder (RVQ-VAE) and a musical teacher based on the Constant-Q Transform (CQT). Furthermore, we explore a wide range of settings to overcome the instability in acoustic language model pre-training, which allows our designed paradigm to scale from 95M to 330M parameters. Experimental results indicate that our model can generalise and perform well on 14 music understanding tasks and attain state-of-the-art (SOTA) overall scores. The code and models are online: https://github.com/yizhilll/MERT. ## 1 Introduction Pre-trained language models (PLMs) can learn generalisable representations of data without human annotated labels in a self-supervised learning (SSL) style, leading to remarkable performance improvement in natural language processing and related fields (Brown et al.,, 2020; Fang et al.,, 2022; Chen et al., 2021a, ). Music is widely recognised as a special language that can be used to communicate across different cultures (Mehr et al.,, 2019). The internal similarity between music and language as a communication interface lays a promising foundation for adapting PLM-based methods to model music sequences. We argue that the benefit is twofold. First, PLMs can potentially pave the way to unify the modelling of a wide range of music understanding, or the so-called Music Information Retrieval (MIR) tasks, including but not limited to music tagging, beat tracking, music transcription, and source separation, so that different tasks no longer need task-specific models or features. Second, releasing a PLM for acoustic music understanding allows the redistribution of the musical knowledge rather than the data itself, which saves the costs of manual annotation and copyright law restrictions. Unfortunately, we are yet to see a general-purpose and cost-effective open-source PLM on acoustic music understanding. Most existing studies are designed to solely address music tagging problems (Pons and Serra,, 2019; Spijkervet and Burgoyne,, 2021; McCallum et al.,, 2022; Huang et al.,, 2022; Zhu et al.,, 2021; Zhao and Guo,, 2021), and many of them do not provide open-source code bases or checkpoints for further evaluation. A promising model is JukeMIR (Castellon et al.,, 2021), which is based on Jukebox (Dhariwal et al.,, 2020) and provides a comprehensive evaluation on MIR downstream tasks. However, this foundation model uses cumbersome hierarchical auto-regressive transformer decoders containing billions of parameters to model music audio, leading to significant inefficiency for conducting general music understanding tasks (e.g., it takes weeks to carry out inference on datasets like MTG (Bogdanov et al.,, 2019) with a consumer-grade 3090 GPU). <details> <summary>x14.png Details</summary>  ### Visual Description ## Diagram Type: Flowchart ### Overview The image is a flowchart that illustrates the process of audio feature extraction and representation using a combination of acoustic and musical models. The chart is divided into several sections, each representing a different step in the process. ### Components/Axes - **Acoustic Teacher**: This section represents the acoustic model, which is used to extract features from audio signals. - **Musical Teacher**: This section represents the musical model, which is used to extract features from musical signals. - **Contextual Representation**: This section represents the process of combining the features extracted from the acoustic and musical models to create a contextual representation of the audio signal. - **Transformer Encoder**: This section represents the use of a transformer encoder to process the contextual representation. - **Masked Audio Features**: This section represents the process of masking audio features to protect the privacy of the data. - **1D Convolution Feature Extractor**: This section represents the use of a 1D convolution feature extractor to extract features from the masked audio features. ### Detailed Analysis - The acoustic model uses a masked audio feature extractor to extract features from the audio signal. - The musical model uses a masked audio feature extractor to extract features from the musical signal. - The contextual representation is created by combining the features extracted from the acoustic and musical models. - The transformer encoder processes the contextual representation to create a final output. - The output is a 1D convolution feature extractor that extracts features from the masked audio features. ### Key Observations - The flowchart shows the process of audio feature extraction and representation using a combination of acoustic and musical models. - The use of a transformer encoder and a 1D convolution feature extractor suggests that the process is designed to be efficient and accurate. - The masking of audio features suggests that the process is designed to protect the privacy of the data. ### Interpretation The flowchart illustrates the process of audio feature extraction and representation using a combination of acoustic and musical models. The use of a transformer encoder and a 1D convolution feature extractor suggests that the process is designed to be efficient and accurate. The masking of audio features suggests that the process is designed to protect the privacy of the data. The contextual representation created by combining the features extracted from the acoustic and musical models suggests that the process is designed to capture the nuances of the audio signal. Overall, the flowchart provides a clear and concise overview of the process of audio feature extraction and representation. </details> Figure 1: Illustration of the MERT Pre-training Framework. The aforementioned research gap has urged us to design and open-source a generalisable and computationally affordable pre-trained acoustic music model. In this paper, we propose an acoustic M usic und ER standing model with large-scale self-supervised T raining (MERT). MERT inherits a speech SSL paradigm, employing teacher models to generate pseudo targets for sequential audio clips. Specifically, to capture the distinctive pitched and tonal characteristics in music, MERT incorporates a multi-task paradigm to balance the acoustic and musical representation learning as demonstrated in Fig. 1. In the proposed design, a Residual Vector Quantisation - Variational Autoencoder (RVQ-VAE) (Défossez et al.,, 2022) is used as the acoustic teacher to provide discretised acoustic-level summarisation of the music signal. The Constant-Q Transformation (CQT) (Brown,, 1991) model is further introduced as the music teacher for capturing pitch and harmonic inductive bias. Regarding the context dependencies and music hierarchies, as indicated in Borsos et al., (2022), we leave the task of modelling high-level and abstract patterns to the stacked layers of self-attentions in the transformer. We also explore a wide range of settings for the transformer and 1D convolution encoder to overcome the instability in acoustic model pre-training, which permits effective scaling up of MERT from 95M to 330M size when blending acoustic and musical knowledge. By scaling up to 330M size (only 7% the size of JukeBox), MERT achieves overall state-of-the-art (SOTA) results on various MIR tasks, which demonstrates a strong generalisability on music understanding. Last but not least, we analyse multiple pre-trained settings considering the teachers and share our decision routes § 5.2 and § 5.3, which could potentially guide future acoustic music understanding pre-training research. To summarise, our contributions are: - proposing a multi-task style predictive acoustic self-supervised learning paradigm, which achieves SOTA performance on various MIR tasks, including important yet unexplored tasks for pre-training such as pitch detection, beat tracking and source separation applications; - conducting a broad range of analysis based on ablation studies of the proposed MERT pre-training paradigm; - exploring robust and stable strategies for acoustic music model training to overcome training instability and frequent crashes when scaling up the pre-training on model size; - providing an open-source, generalisable and computationally affordable acoustic music pre-trained model, which addresses the needs of both industry and research communities. ## 2 Related Work #### PLMs for Acoustic Music The field of music information retrieval (MIR) has long been facing challenges in data availability due to the costs associated with music audio annotation and country-specific copyright laws (Chen et al.,, 2019; Castellon et al.,, 2021). To address this challenge, pre-trained language models (PLMs) for acoustic music have been proposed to provide reusable learned representations, enabling transfer learning for various downstream MIR tasks without the need for extensive data annotation (Castellon et al.,, 2021). However, current acoustic music pre-trained models still have room for improvement in terms of providing open-source, generalisable, and lightweight learned representations suitable for both industrial and research applications (McCallum et al.,, 2022). Existing acoustic music pre-trained models primarily focus on tagging tasks and rely on supervised tagging labels for pre-training (Pons and Serra,, 2019; Spijkervet and Burgoyne,, 2021; McCallum et al.,, 2022; Huang et al.,, 2022). While some studies have explored contrastive learning for acoustic music pre-training, they face limitations in training data and model size, hampering the performance improvements (Choi et al.,, 2017; Li et al.,, 2022). Additionally, several models trained on inaccessible datasets or without publicly available codes and model weights make it difficult to reproduce or extend their approaches (McCallum et al.,, 2022; Castellon et al.,, 2021; Li et al.,, 2022; Zhu et al.,, 2021; Zhao and Guo,, 2021). Although some general-purpose audio representation models show potential for music audio representation learning, their performance is mostly evaluated on limited MIR downstream tasks (Saeed et al.,, 2021; Borsos et al.,, 2022; Wang et al.,, 2023). This lack of comprehensive evaluation hinders further studies and a thorough understanding of the pros and cons of existing models. #### Self-Supervised Speech Processing Music and speech processing are closely related (Jasmin et al.,, 2020) since they usually use the same audio data formats. Additionally, both acoustic music and speech processing models need to deal with the cocktail party problem (Brown and Bidelman,, 2022; Petermann et al.,, 2022) since good source separation capabilities help both separating noises and background sounds with speech and processing polyphonic music audio. These common grounds between music and speech processing inspire us to adapt SOTA speech pre-trained models and tailor them specifically for music audio processing tasks. For instance, existing research work targeting general-purpose audio representations (Saeed et al.,, 2021; Borsos et al.,, 2022; Wang et al.,, 2023) has verified that self-supervised speech processing models can be extended beyond speech to downstream entry-level music tasks, including generating mono piano music and music reconstruction. #### Audio Representation with Language Modelling Mask strategy-based large-scale language models have been applied to a wide range of domains (Lample and Charton,, 2019; Chen et al., 2021a, ; Chen et al., 2021b, ; Fang et al.,, 2022), but still remain under-explored in acoustic music understanding. For audio, Dhariwal et al., (2020) investigates generating hierarchical tokens which can be further employed to reconstruct music, inspiring subsequent research to understand and generate acoustic music based on extracted discrete tokens from continuous features. Baevski and Mohamed, (2020) introduce a pre-trained VQ-VAE (Baevski et al.,, 2019) to provide prediction targets to conduct speech representation learning with MLM. While introducing K-means to provide discrete token codebooks and pre-training the model to detect sound units, Hsu et al., (2021) claim that a better teacher model in SSL could lead to better downstream task performance. Additionally, recent speech processing pre-trained models (Borsos et al.,, 2022; Wang et al.,, 2023) propose to train or adopt separately trained codecs (Zeghidour et al.,, 2021; Défossez et al.,, 2022) for discrete token extraction. Based on the conclusion from previous studies, the recently released RVQ-VAEs (Zeghidour et al.,, 2021; Défossez et al.,, 2022), achieving good results in music reconstruction, could be adopted as teacher models for music understanding pre-training and provide acoustic information guidance. Yet some of the uniqueness of music processing such as timbre and harmony remains unexplored. We thus propose to incorporate a corresponding musical teacher model in MERT to fill such an important gap. ## 3 Methodology This section introduces the pre-training paradigm and architecture of our models. It includes prediction to acoustic teachers such as k-means or deep music features, and reconstruction to music teachers such as CQT spectrum, both based on the well-established masked language modelling (MLM). ### 3.1 Pre-training with MLM Supervised Learning requires a labelled dataset $D_t=\{x_i^(t),y_i^(t)\}^N_i=1$ . Here, $N$ is the number of data samples, $x_i^(t)$ is the $i^th$ data sample in the dataset, and $y_i^(t)$ is the corresponding label. From $D_t$ , we can train a machine learning algorithm $f_θ≤ft(·\right)$ parameterised with $θ$ that makes label predictions on each data sample. Unsupervised learning, in contrast, learns an algorithm based on an unlabelled dataset $D=\{x_i\}^M_i=1$ , with SSL being a specific type of this class. For each data sample $x_i$ , SSL derives a new data $x_i^\prime$ with a pseudo label $y_i^\prime$ . The training process is to minimise the loss between each pseudo label $y_i^\prime$ and the prediction based on new data $\hat{y}_i=f_θ(x_i^\prime)$ as denoted in Eq. 1. $$ θ^∗={arg min}_θ∑_x_{i^(t)∈ D}L≤ft(f_ θ(x_i^\prime(t)),y_i^\prime(t)\right). \tag{1} $$ MLM is a famous example of pseudo-label generation. Let $x_i=≤ft[x_i^(1),x_i^(2),⋯,x_i^(L)\right]$ be the $i^th$ data sample in a sequential dataset with length $L$ , and $M⊂[L]$ is a subset of indices randomly chosen from $1$ to $L$ . Then, the new data is defined by the following equation $$ x_i^\prime=≤ft[1_[L]∖ M(1)· x_i^(1),1 _[L]∖ M(2)· x_i^(2),⋯,1_[L]∖ M(L) · x_i^(L)\right] \tag{1} $$ where $1_[L]∖ M(x)$ denotes the indicator function, that is, $1_[L]∖ M(x)=1$ if and only if $x$ is outside the masked indices set $M$ . The pseudo-label that needs to be learned is typically $y_i^\prime=x_i-x_i^\prime$ , i.e., the masked data. However, reconstructing masked data $y^\prime$ for raw audio tasks as pseudo-labels is hard to train. HuBERT (Vaswani et al.,, 2017; Hsu et al.,, 2021) uses a dimension-reduced feature $z^\prime$ derived from $y^\prime$ with phonetic acoustic information, which forms the design basis of our pre-training strategy. As a speech SSL system, HuBERT utilises offline clustering to acquire pseudo labels for a BERT-like prediction loss. Specifically, it uses Mel-frequency cepstral coefficients (MFCCs), a widely-used traditional feature in speech-related tasks, as acoustic features for clustering. The obtained results are then utilised as pseudo labels in the first iteration of pre-training. It then uses the learned representation for clustering to get a pseudo label for the second iteration pre-training. Such a pseudo label includes acoustic information in human speech and can be aligned to phonemes. The loss functions of HuBERT are formulated as follows: $$ L_H(f;x,M,Z)=∑_t∈ M\log p_f(z_t\mid x^\prime,t) \tag{3} $$ where $\log p_f(·\mid x^\prime,t)$ is the log-likelihood function on clustering results given the masked input $x^\prime$ and position $t$ derived from $f$ ; likelihood function $p_f$ is the Noise Contrastive Estimation (NCE) loss which is defined as $$ p_f(c\mid x^\prime,t)=\frac{\exp(sim(T(o_t),e_c)/τ)}{∑_c ^\prime=1^C\exp(sim(T(o_t),e_c^\prime)/τ)}, \tag{4} $$ Here, $c∈[C]$ is a codeword of the clustering results and $e_c$ represents its embedding; sim is the cosine similarity; $o_t$ is the output of the model at timestep $t$ ; and $T(o_t)$ is the linear transformation of $o_t$ , making it have the same dimension as $e_c$ . Besides, $τ$ scales the logit which is set to $0.1$ in HuBERT. The linear transformation $T$ , the model to generate outputs, and the embedding of all the clustering results are all learnable. Overall, we use the same model as HuBERT but introduce several notable variations tailored to music. Specifically, we designed a better hidden-unit $z$ as pseudo tags for pre-training with multiple music acoustic features. In addition, we added a reconstruction loss to music features and employed additional music augmentation tricks. ### 3.2 Modelling Acoustic Information The MFCC features are only good at modelling acoustic and timbre information for single-pitch signals, and therefore, the clustering results do not provide much timbre information in music recordings. We proposed two potential approaches as the teacher on acoustic information: one based on traditional features, and the other based on deep learning. The first method uses k-means on the log-Mel spectrum and Chroma features for timbre and harmonic acoustic information, respectively. In the case of music representations, each frame contains more information compared to speech, necessitating a larger number of classes for k-means clustering. The complexity of the k-means algorithm is linear with the number of centroids (clustering centres), leading to a time-consuming k-means for the music feature. To tackle this problem, we employ 300-means for the log-Mel spectrum with dimension 229, and 200-means for Chroma features with dimension 264, resulting in a total of 60,000 classes (200 centroids for Chroma features multiplied by 300 centroids for the log-Mel spectrum). Despite the increased number of classes, the computational complexity remains comparable to that of HuBERT. The disadvantage of k-means is that it is difficult to scale up to a larger number of classes and larger datasets, and the results are sensitive to initialisation. The second choice for our acoustic teacher is EnCodec (Défossez et al.,, 2022), a recent learnable feature with 8-layer residual Vector Quantized-Variational AutoEncoder (VQ-VAE). Each acoustic feature, denoted as $z_enc∈[C]^L× 8$ , is a 2-dimensional auditory code matrix, and $L$ is the length of the recording. The row vector of each matrix $z_enc[t,:]$ represents the results of $8$ different clusterings for frame $t$ , and the column vector of each matrix $z_enc[:,j]$ represents the results from the $j^th$ codebook of the audio sequence, where $j∈\{1,…,8\}$ . EnCodec converts 24kHz input waveforms to 8 different embeddings at 75Hz with a 320-fold reduction, and the quantizer has $1024$ dimensions. In this setting, for each 5-second waveform, the discrete acoustic feature is a matrix with $375× 8$ entries, representing 375 frames (75Hz × 5s) and 8 deep acoustic features. With these embeddings, the decoder of EnCodec can reconstruct the waveform at 24 kHz with authentic information in timbre. ### 3.3 Modelling Musical Information Apart from acoustic information, we added a new reconstruction loss to the Constant-Q transform (CQT) spectrogram to emphasise pitch-level information. The CQT is a type of frequency transform that is widely used in various MIR tasks, such as pitch detection, chord recognition, and music transcription. It is similar to the Fourier transform, but bin widths are proportional to frequency rather than equal, giving each octave the same number of bins, resulting in a better time-frequency trade-off for music audio where multiple pitches occur in multiple octaves. We utilize mean squared error (MSE) loss to reconstruct the CQT spectrum $z_cqt$ from the masked input audio $x^\prime$ . That is, $$ L_CQT(f_cqt;x,M,z_cqt)=∑_t∈ M≤ft\|z_cqt,t- f_cqt(x^\prime)_t\right\|_2 \tag{5} $$ And the final loss function $L$ is a linear combination of both the acoustic loss function $L_H$ and the musical-pitch loss function $L_CQT$ : $$ L=α·L_H+L_CQT \tag{6} $$ ## 4 Experiments ### 4.1 Evaluation Protocol #### Downstream Tasks We evaluate our method and compare it with baseline models on 14 downstream tasks, including frame-level classification or regression tasks like music tagging, key detection, genre classification, emotion score regression, instrument classification, pitch classification, vocal technique detection, and singer identification; and sequential tasks like beat tracking and source separation. For instrument classification, we use the Nsynth (Engel et al.,, 2017) and MTG-instrument datasets, with receiver operating characteristic (ROC), and average precision (AP). The NSynth dataset is also used for pitch classification, with accuracy (ACC) as the evaluation metric. Vocal technique detection and singer identification based on the VocalSet dataset (Wilkins et al.,, 2018), with accuracy as the metric. For music tagging, we utilise the MagnaTagATune (MTT) (Law et al.,, 2009) and MTG-Jamendo (Bogdanov et al.,, 2019) datasets, averaging multiple embeddings for long audio recordings. Key detection is accomplished using the Giantsteps and Giantsteps-MTG-keys datasets (Knees et al.,, 2015; Korzeniowski and Widmer,, 2017), with a refined accuracy (ACC refined) metric. Genre classification is performed using the GTZAN (Tzanetakis and Cook,, 2002) and MTG-Genre datasets, with ROC, and AP metrics. Emotion score regression is conducted on the Emomusic dataset (Soleymani et al.,, 2013), with the coefficient of determination (R2 score) of arousal and valence as evaluation metrics. Beat tracking is conducted on the GTZAN Rhythm dataset (Marchand and Peeters,, 2015), using the F-measure (F1). Finally, source separation is accomplished using the MUSDB18 dataset (Rafii et al.,, 2017), with the Source-to-Distortion Ratio (SDR) as the evaluation metric. The full descriptions of the datasets and tasks can be found in Appendix B.1. #### Probing Protocol Following Castellon et al., (2021); Yang et al., (2021), we restrict the testing protocol with probing rather than fine-tuning, i.e. freezing the backbone pre-trained models as deep feature extractor and only train a simple downstream structure, typically a multilayer perceptron (MLP) for frame-level tasks. For a fair comparison, we also limit the space for hyper-parameter search. For full details please refer to Appendix B.2. ### 4.2 Baseline Methods We select models pre-trained with various paradigms from both music and speech domains as our baselines to provide a comprehensive evaluation of the generalisation ability of the designs. MusiCNN (Pons and Serra,, 2019) is selected as a representative supervised method, which is pre-trained with supervision from the Million Song Dataset tags (Bertin-Mahieux et al.,, 2011). CLMR (Spijkervet and Burgoyne,, 2021) and MULE (McCallum et al.,, 2022) are selected as representatives of SOTA music representations trained with contrastive learning. Jukebox (Dhariwal et al.,, 2020) and the corresponding transfer learning method, JukeMIR (Castellon et al.,, 2021) is selected as the representative of transfer learning from a large-scale generative pre-trained musical representation. We also select the recently proposed strong speech SSL models, HuBERT (Hsu et al.,, 2021) and data2vec (Baevski et al.,, 2022), as our baselines since they share the same MLM pre-training paradigm with MERT. While HuBERT reconstructs the masked discrete tokens provided by the K-means teacher, data2vec uses the student model updated with an exponential moving average gradient to produce continuous representations for MLM prediction. In order to reveal the effectiveness of the pre-training paradigm itself rather than the training data distribution, we re-train the speech models and denote them by HuBERT music and data2vec music. Additionally, we present the current SOTA for each task including results from both supervised and self-supervised methods. ### 4.3 Implementation Details #### Training Settings We deploy the proposed SSL architecture in the training of various model sizes with matched scales of data. We mined 160K hours of music recordings from the Internet to build a large-scale music dataset. Accordingly, the base size models (95M) are trained with a 1K hours subset whereas the whole dataset is used for the large model (330M). Specifically, we provide a special edition of the base model, MERT-95M-public, that is trained on a totally publicly available music dataset, music4all (Santana et al.,, 2020), with a data size of 910 hours. In the context of self-attention, the computational complexity scales quadratically with the sequence length. Therefore, when dealing with limited computational resources, there exists a trade-off between the batch size and the sequence length. In our preliminary experiments, we have observed that increasing the batch size provides greater performance improvements compared to extending the context length. To allow a larger batch size under the computational limitation, we adopt a strategy of randomly truncating audio clips into 5-second segments following Ma et al., (2023). This duration roughly corresponds to a 2-bar context in music. It is worth noting that our model utilises a convolutional relative positional embedding, similar to the approach introduced by Baevski et al., (2020) in Wav2Vec, enabling it to operate effectively in longer contexts, if required. The effective batch sizes and learning rates for the base model and large model are set to $1.5$ and $5.5$ hours, and their learning rates are set to $5e{-4}$ , $1.5e{-3}$ , respectively. Pre-training is carried out with the fairseq https://github.com/facebookresearch/fairseq framework. Models are trained with 64 A100-40GB GPUs with fp16. We also implement a data augmentation of randomly adding short segments to improve the representation robustness, and describe the details in Appendix A.1. #### Training Stability In our empirical findings, we observe that when scaling up acoustic encoder-only models, they tend to exhibit a higher susceptibility to training instability compared to models of similar size in text or image domains. Such instability can result in decreased performance or, in extreme cases, even lead to crashes in model training. During experimentation with scaling up to the MERT-330M model, we encounter notable instability manifested by constant gradient clipping and sporadic spikes in losses. This instability has a detrimental effect on the accuracy of MLM predictions and results in decreased performance on downstream tasks. Our attempts to resume training from previously saved checkpoints and data batches are proved unsuccessful in mitigating the instability issue. Furthermore, we observe that reducing the learning rate in this context not only fails to address the issue but also leads to a decline in performance and hindered the training convergence. We further explore the effectiveness of a seemingly-powerful method DeepNorm (Wang et al., 2022a, ) in stabilising acoustic language model pre-training, but find it to be ineffective. Eventually, we discover that incorporating attention relaxation techniques (Chen et al., 2021b, ) is beneficial in addressing the instability challenges. We also found that transitioning from post-layer normalisation (Post-LN) to pre-layer normalisation (Pre-LN) offers a potential solution of allowing training to continue. More information can be found in Appendix B.3. Table 1: Experimental Performance of MERT and Baselines on Downstream Tasks (1/2). The baselines are grouped by supervised and unsupervised pre-training paradigms. The superscripts denote the category of the acoustic teacher used by MERT models. “public” refers to the MERT model trained with only open-source dataset. Results with star* are claimed in the references. | Dataset | MTT | GS | GTZAN | GTZAN | EMO | Nsynth | VocalSet | VocalSet | | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Task | Tagging | Key | Genre | Rhythm | Emotion | Instrument | Pitch | Tech | Singer | | | | Metrics | ROC | AP | Acc Refined | Acc | F1 beat | R2 V | R2 A | Acc | Acc | Acc | Acc | | MusiCNN [41] | 90.6* | 38.3* | 12.8* | 79.0* | - | 46.6* | 70.3* | 72.6 | 64.1 | 70.3 | 57.0 | | CLMR [48] | 89.4* | 36.1* | 14.9* | 68.6* | - | 45.8* | 67.8* | 67.9 | 47.0 | 58.1 | 49.9 | | Jukebox-5B [15; 57] | 91.5* | 41.4 * | 66.7* | 79.7* | - | 61.7 * | 72.1* | 70.4 | 91.6 | 76.7 | 82.6 | | MULE [36] | 91.4* | 40.4* | 66.7* | 73.5* | - | 57.7* | 70.0* | 74.0* | 89.2* | 75.5 | 87.5 | | HuBERT-base music [25] | 90.2 | 37.7 | 14.7 | 70.0 | 88.6 | 42.1 | 66.5 | 69.3 | 77.4 | 65.9 | 75.3 | | data2vec-base music [2] | 90.0 | 36.2 | 50.6 | 74.1 | 68.2 | 52.1 | 71.0 | 69.4 | 93.1 | 71.1 | 81.4 | | MERT-95M K-means | 90.6 | 38.4 | 65.0 | 78.6 | 88.3 | 52.9 | 69.9 | 71.3 | 92.3 | 74.6 | 77.2 | | MERT-95M-public K-means | 90.7 | 38.4 | 67.3 | 72.8 | 88.1 | 59.7 | 72.5 | 70.4 | 92.3 | 75.6 | 78.0 | | MERT-95M RVQ-VAE | 91.0 | 39.3 | 63.5 | 78.6 | 88.3 | 60.0 | 76.4 | 70.7 | 92.6 | 74.2 | 83.7 | | MERT-330M RVQ-VAE | 91.3 | 40.2 | 65.6 | 79.3 | 87.9 | 61.2 | 74.7 | 72.6 | 94.4 | 76.9 | 87.1 | | (Previous) SOTA | 92.0 [26] | 41.4 [15] | 74.3 [30] | 83.5 [36] | 80.6 [24] | 61.7 | 72.1 [15] | 78.2 [53] | 89.2 [36] | 65.6 [55] | 80.3 [39] | Table 2: Experimental Performance of MERT and Baselines on Downstream Tasks (2/2). Average scores across task are calculated on the SOTA results and models applicable to all the tasks. | Dataset | MTG | MTG | MTG | MTG | MUSDB | Avg. | | | | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Task | Instrument | MoodTheme | Genre | Top50 | Source Seperation | | | | | | | | | | Metrics | ROC | AP | ROC | AP | ROC | AP | ROC | AP | SDR vocals | SDR drums | SDR bass | SDR other | | | MusiCNN [41] | 74.0 | 17.2 | 74.0 | 12.6 | 86.0 | 17.5 | 82.0 | 27.5 | - | - | - | - | - | | CLMR [48] | 73.5 | 17.0 | 73.5 | 12.6 | 84.6 | 16.2 | 81.3 | 26.4 | - | - | - | - | - | | Jukebox-5B [15; 57] | - | - | - | - | - | - | - | - | 5.1* | 4.9* | 4.1* | 2.7* | - | | MULE [36] | 76.6 | 19.2 | 78.0 | 15.4 | 88.0 | 20.4 | 83.7 | 30.6 | - | - | - | - | - | | HuBERT-base music [25] | 75.5 | 17.8 | 76.0 | 13.9 | 86.5 | 18.0 | 82.4 | 28.1 | 4.7 | 3.7 | 1.8 | 2.1 | 55.8 | | data2vec-base music [2] | 76.1 | 19.2 | 76.7 | 14.3 | 87.1 | 18.8 | 83.0 | 29.2 | 5.5 | 5.5 | 4.1 | 3.0 | 59.9 | | MERT-95M K-means | 77.2 | 19.6 | 75.9 | 13.7 | 87.0 | 18.6 | 82.8 | 29.4 | 5.6 | 5.6 | 4.0 | 3.0 | 62.9 | | MERT-95M-public K-means | 77.5 | 19.6 | 76.2 | 13.3 | 87.2 | 18.8 | 83.0 | 28.9 | 5.5 | 5.5 | 3.7 | 3.0 | 63.0 | | MERT-95M RVQ-VAE | 77.5 | 19.4 | 76.4 | 13.4 | 87.1 | 18.8 | 83.0 | 28.9 | 5.5 | 5.5 | 3.8 | 3.1 | 63.7 | | MERT-330M RVQ-VAE | 78.1 | 19.8 | 76.5 | 14.0 | 86.7 | 18.6 | 83.4 | 29.9 | 5.3 | 5.6 | 3.6 | 3.0 | 64.7 | | (Previous) SOTA | 78.8 | 20.2 [1] | 78.6 | 16.1 [36] | 87.7 | 20.3 [1] | 84.3 | 32.1 [36] | 9.3 | 10.8 | 10.4 | 6.4 [44] | 64.5 | ## 5 Results Analysis ### 5.1 Performance & Efficiency of MERT Models The results on all the downstream tasks are provided in Tab. 1 and Tab. 2. As suggested by the average scores in Tab. 2, MERT-330M RVQ-VAE achieves the same score as the combination of the previous SOTAs (from 10 different models even including supervised methods) and becomes the new SOTA on 4 metrics. It is also noteworthy that the other smaller MERT-95M s still have comparable performance. Generally, MERTs perform well on tasks focusing on local-level musical information such as beat, pitch and local timbre such as singer information, and remain competitive on the other tasks requiring more global-level information, such as music tagging, key detection, and genre classification. This indicates the blending of acoustic and musical teachers could provide comprehensive guidance for the understanding of music recordings, though pre-trained in only a 5-second context length. Nevertheless, the performances of our models in tasks with more global music information are close to strong baselines, suggesting MERT models are capable of recognising global patterns well, thanks to the relative position embeddings and the contextualisation of the transformers. In addition, our models demonstrate good results with limited data, even when training with public data that may lack enough diversity. MERT-95M-public and MERT-95M are both trained on a $∼$ 1k hour dataset and give competitive performance compared with the SOTA and MERT-330M, proving that MERT can converge effectively and learns generalisable music representations with limited training data. Moreover, the MERT-95M-public is trained with Music4ALL (Santana et al.,, 2020), a 910-hours public music dataset with mainly pop music and lack of diversity in music style, and shows comparable performance to other settings. In particular, its performance does not have a significant difference besides genre classification on GTZAN compared to MERT-95M. We evaluate the performance of the MERT RVQ-VAE model with a parameter size of 95M and 330M, given the use of the EnCodec feature enables us to scale up the dataset compared to the K-means. The results demonstrate that increasing the model size to 330M yields improved performance or maintains similar performance compared to MERT-95M RVQ-VAE (less than 0.1%) on most of the tasks besides beat tracking. More importantly, the lightweight sizes of MERTs open up new possibilities for transferring one general understanding model for large-scale classification or sequence labelling MIR tasks. MERT series models achieve better or comparable performance with only $1.9\$ (95M) and $6.6\$ (330M) parameters compared to the self-supervised baseline Jukebox-5B (Dhariwal et al.,, 2020). Even when our evaluation is in probing setting, most models could not be trained on sequence labelling tasks like beat tracking or source separation with affordable computational costs except for MERT and baseline models with similar architecture (Hsu et al.,, 2021; Baevski et al.,, 2022). Table 3: Evaluation Results from Models Trained with Different Teacher Settings. Models labeled with △2 and ▲2 suggest that the K-means teachers are trained with the features from △1 and ▲1 models. All the listed models are sized in (95M) and not augmented with the in-batch noise mixture. | Acoustic Teacher | Acoustic Target Class | Musical Teacher | MTT | GS | GTZAN | EMO | Avg. | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Tagging | Key | Genre | Emotion | | | | | | | | ROC | AP | Acc Refined | Acc | R2 V | R2 A | | | | | | K-means MFCC | 100 | N/A | 89.8 | 36.3 | 15.1 | 66.2 | 39.6 | 67 | 49.4 | | K-means MFCC | 500 | 90.3 | 38 | 17 | 70 | 40.6 | 67.5 | 51.3 | | | K-means MFCC | 2000 △1 | 90.2 | 37.6 | 15.6 | 70 | 44.3 | 67.6 | 51.4 | | | K-means Logmel+Chroma | 300 + 200 ▲1 | 90.5 | 37.6 | 55.1 | 75.2 | 40.1 | 68.2 | 62.1 | | | K-means MFCC | 2000 △2 | 90.4 | 37.5 | 16.1 | 68.3 | 43.9 | 67.7 | 51.0 | | | K-means Logmel+Chroma | 500 ▲2 | 90.4 | 37.7 | 49.2 | 72.8 | 46.5 | 66.9 | 60.7 | | | K-means MFCC+CQT | 300+200 | 89.4 | 35.3 | 53.2 | 69.0 | 45.8 | 66.8 | 60.2 | | | 2-9 K-means Logmel+Chroma | 300 + 200 | CQT | 90.6 | 38.4 | 65.0 | 78.6 | 53.1 | 68.7 | 67.3 | | RVQ-VAE | 1024 $×$ 8 all codebook | N/A | 90.7 | 38.7 | 60.5 | 72.8 | 55.3 | 69.0 | 65.0 | | 2-9 | 1024 $×$ 8 all codebook | CQT | 90.5 | 38.4 | 63.2 | 77.2 | 53.2 | 72.3 | 66.9 | | 1024 codebook7 | 88.6 | 34.4 | 63.5 | 62.1 | 33.3 | 53.2 | 57.6 | | | | 1024 codebook0 | 90 | 36.7 | 59.4 | 67.2 | 39.7 | 64.5 | 60.5 | | | | 1024 $×$ 8 random codebook | 90.6 | 38.1 | 66.8 | 73.8 | 48.1 | 68.6 | 65.8 | | | ### 5.2 The Effectiveness of Acoustic & Musical Teacher As demonstrated in Tab. 3, we explore optimal combinations and selections of the teacher models in the MERT paradigm with a subset of downstream tasks following Castellon et al., (2021), including auto-tagging, key detection, genre classification, and emotion recognition. We reproduce the original HuBERT (Hsu et al.,, 2021) setting on music datasets with the acoustic teacher K-means MFCC $\vartriangle 1$ and the teacher K-means MFCC $\vartriangle 2$ trained on features produced by HuBERT model from the first stage, similar to DeepCluster (Caron et al.,, 2018). We observe that such models perform poorly on the key detection and emotion recognition tasks even we increase the dimension of the MFCC features from $100$ to $2000$ . As the re-clustering K-means does not bring significant improvement in the second stage pre-training, we stick to the ordinary one stage pre-training to study the influence brought by the teachers with less computational cost. Given that the key information is highly related to the pitch classes of the audio, we then introduce such inductive bias by providing the K-means acoustic teacher with additional Chroma or CQT features, denoted as K-means Logmel+Chroma $\blacktriangle 1$ and K-means MFCC+CQT. The additional pitch information indirectly brought by the Chroma and CQT features immediately endow the model a certain of level of key detection ability and raise the accuracy from $15.6$ to $55.1$ and $53.2$ while keeping or increasing performances on other tasks. This confirms that the potentials of transformer models can be better excavated from more dimensions by introducing extra pseudo prediction targets in the MLM scheme. Following such an intuition, it could be further assumed that designing a proper multi-task learning pre-training paradigm can guide the model to produce more general representations for various music understanding tasks. We thus propose leveraging the CQT explicitly as a musical teacher to introduce harmonic inductive bias during the pre-training. Compared to models trained with only the acoustic teacher MFCC $\vartriangle 1$ or K-means Logmel+Chroma $\blacktriangle 1$ , MERT models trained with the newly proposed CQT musical teacher that are naturally more aligned to music audio can achieve significant performance gains on not only the key detection task but also the tasks requiring the high-level information like genre classification and emotion recognition. However, given that K-means models are difficult to scale up on large datasets due to memory and computational requirements, we use the RVQ-VAE model EnCodec (Défossez et al.,, 2022) as the final version of acoustic teacher without searching for the immeasurable hyper-parameter $K$ . The EnCodec could intuitively provide more comprehensive acoustic information since the audio can be greatly recovered from the intermediate discrete codecs from the encoder by a neural decoder. We observe that leveraging only one top (1024 codebook7) or bottom layer (1024 codebook0) of the residual codebooks in RVQ-VAE already provide substantial information in pre-training, and the use of all layers in the codebooks allows the student models to learn richer acoustic patterns. Although the strategy of randomly accessing one of the codebooks for each batch can alleviate the use of GPU memory and lead to similar performance compared to using all of them at a time, the setting of predicting 8 coodebooks together is adopted for faster convergence in the finalised design. By replacing the acoustic teacher with RVQ-VAE, MERT achieves an average score of $66.9$ , similar to that of the K-means Logmel+Chroma $\blacktriangle 1$ version (i.e., $67.3$ ) while largely reducing the cost of scaling up K-means. ### 5.3 Study on Musical Loss Table 4: Evaluation Results for Musical Loss Study. The listed models are not augmented with the in-batch noise mixture. | Parameter Size | Acoustic Teacher Model | Acoustic Target Class | Musical Loss Weight | MTT | GS | GTZAN | EMO | Avg. | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Tagging | Key | Genre | Emotion | | | | | | | | | ROC | AP | Acc Refined | Acc | R2 V | R2 A | | | | | | | 95M | K-means Logmel+Chroma | 300 + 200 | N/A | 90.5 | 37.6 | 55.1 | 75.2 | 40.1 | 68.2 | 62.1 | | 1 | 90.6 | 38.4 | 65.0 | 78.6 | 53.1 | 68.7 | 67.3 | | | | | 2 | 90.6 | 38.1 | 62.7 | 66.9 | 45.5 | 67.9 | 62.7 | | | | | 5 | 90.4 | 37.3 | 65.3 | 70.3 | 45.7 | 68.3 | 64.1 | | | | | 95M | RVQ-VAE | 1024 $×$ 8 all codebook | N/A | 90.7 | 38.7 | 60.5 | 72.8 | 55.3 | 69.0 | 65.0 | | 1024 $×$ 8 all codebook | 1 | 90.5 | 38.4 | 63.2 | 77.2 | 53.2 | 72.3 | 66.9 | | | We conducted a hyperparameter search to determine the optimal weight for the musical loss applied to masked audios in the k-means setting. In Table 4, we present the results of the varying musical loss weights, which uses the same evaluation setting in § 5.2. By adjusting the weight, we find that a weight of $1$ yielded the best overall performance for the base model. We observe that when switching the acoustic teacher to RVA-VAE, the models performs slightly worse on GS than those with K-means. Overall, our study provides valuable insights into the impact of musical loss and different acoustic models on the performance of the acoustic language model. These findings can inform the future development of more effective and efficient models in the domain of acoustic processing. ## 6 Conclusion In conclusion, our work underscores the potential of SSL for modelling raw music audio and the efficacy of our approach, MERT, in pre-training sizeable models. We present a novel paradigm that integrates RVQ-VAE and CQT teacher models, providing a unique blend of acoustic and musical information necessary for MLM-based pre-training for music understanding. This integration, bolstered by the application of an in-batch noise mixup data augmentation and Pre-LN, enables the learning of robust music representations with further training stability. The performance of the MERT model surpasses previous SSL baselines, achieving SOTA or comparable results across a wide range of MIR tasks while using significantly smaller parameter size. We anticipate that our method and the forthcoming public release of our codes and models will catalyse further research into the application of SSL in music audio, thereby broadening the scope and depth of human understanding of music. Despite being capable of handling longer sequences with relative positional embedding, our models are limited by the short 5-second training context, so our approach could be further improved for tasks requiring understanding extended musical contexts if trained on longer sequences. ## Limitations and Future Work Our models are trained using only 5-second audio signals due to constraints in computational resources and the extended length of audio signals. Despite these models being capable of handling longer sequences thanks to relative positional embedding, this approach could potentially limit their performance in tasks requiring a comprehensive understanding of extended musical contexts. We plan to continue training our models on a longer context once gaining access to more computing resources. Moreover, although we propose several techniques to improve the training stability for the acoustic pre-training, we still suffer from the gradient exploding issues with the half-precision training for settings with larger batch sizes and model sizes. In addition, we observe inverse-scaling effect in specific tasks while scaling-up to 330M, which indicates that our design could be further improved by stabilising the training. ## Acknowledgements This paper is a tribute to our talented friend Anqiao Yang, for his friendship and valuable advice to this work. Yizhi Li is a Ph.D. student fully funded by the Department of Computer Science, University of Manchester, UK. This work is partially funded by Theme based Research Scheme (T45-205/21-N), Research Grants Council of Hong Kong. Yinghao Ma is a research student at the UKRI Centre for Doctoral Training in Artificial Intelligence and Music, supported by UK Research and Innovation [grant number EP/S022694/1]. 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Musicbert: A self-supervised learning of music representation. In Proceedings of the 29th ACM International Conference on Multimedia, pages 3955–3963. ## Appendix A Methodology ### A.1 Robust Representation Learning Algorithm 1 Pseudocode description of the pre-training loss calculation in Python style. ⬇ 1 def loss_cal (x_batch, x_acoustic_labels): 2 # retrieve embeddings for acoustic class 3 y_VQ = embedding (x_acoustic_labels) 4 # prepare CQT targets 5 y_CQT = compute_CQT (x_batch) 6 # conduct in-batch mixture 7 x_noised = mixture (x_batch) 8 # compute the representations 9 z = MERT (x_noised) 10 11 # loss calculation 12 loss_acoustic = Cross_Entropy (z [mask_idx], y_VQ [mask_idx]) 13 loss_musical = Mean_Square_Error (z [mask_idx], y_CQT [mask_idx]) 14 return loss_acoustic, loss_musical We introduce “in-batch noise mixup” for music SSL. The mixup augmentation refers to the audio clip being added up with a certain ratio of shorter audio excerpts to form an augmented single sample during pre-training, instead of using the original audio. We randomly sample the audio segments from the same batch and add them to audio at random positions according to some probability. Theoretically, sampling from the whole training dataset would provide more randomness and thus be more beneficial to the representation robustness, but we narrow the sampling pool to the same audio batch considering the limited computational resources. The mixup could enable the learning of more robust musical representations and force the model to focus on the useful musical source and to ignore the noise. A pseudocode implementation can be found in Algo. 1. Using the same evaluation setting in § 5.2, we alter the in-batch mixup probability to evaluate whether it is affecting the performance of the model when compound with musical loss. We found the mixup probability provides worse results in MERT K-means but provides better performance for MERT RVQ-VAE. Therefore, we determined a probability of $0.5$ to be suitable based on the average performance score, and set it as a hyper-parameter in the final released model. Such a phenomenon deserves more attention. Table 5: Evaluation Results for Pre-training Setting Ablation Study. | Parameter Size | Acoustic Teacher Model | Acoustic Target Class | Musical Loss Weight | In-batch Mixup Probability | MTT | GS | GTZAN | EMO | Avg. | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Tagging | Key | Genre | Emotion | | | | | | | | | | ROC | AP | Acc Refined | Acc | R2 V | R2 A | | | | | | | | 95M | K-means Logmel+Chroma | 300 + 200 | N/A | N/A | 90.5 | 37.6 | 55.1 | 75.2 | 40.1 | 68.2 | 62.1 | | 1 | N/A | 90.6 | 38.4 | 65.0 | 78.6 | 53.1 | 68.7 | 67.3 | | | | | 2 | N/A | 90.6 | 38.1 | 62.7 | 66.9 | 45.5 | 67.9 | 62.7 | | | | | 5 | N/A | 90.4 | 37.3 | 65.3 | 70.3 | 45.7 | 68.3 | 64.1 | | | | | 1 | 0.25 | 90.6 | 37.9 | 65.5 | 70.0 | 49.6 | 72.5 | 65.2 | | | | | 1 | 0.5 | 90.7 | 38.6 | 64.9 | 72.8 | 45.3 | 71.9 | 65.2 | | | | | 95M | RVQ-VAE | 1024 $×$ 8 all codebook | 1 | N/A | 90.5 | 38.4 | 63.2 | 77.2 | 53.2 | 72.3 | 66.9 | | 95M | 1024 $×$ 8 all codebook | 1 | 0.5 | 91.0 | 39.3 | 63.3 | 78.6 | 60.0 | 76.4 | 68.8 | | ### A.2 The Effectiveness of Vanilla RVQ-VAE Rrepresentation Table 6: Evaluating the EnCodec RVQ-VAE Embeddings. | Dataset | MTT | GS | GTZAN | EMO | VocalSet | VocalSet | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Task | Tagging | Key | Genre | Emotion | Tech | Singer | | | | Metrics | ROC | AP | Acc Refined | Acc | R2 V | R2 A | Acc | Acc | | RVQ-VAE Embedding | 83.4 | 26.2 | 12.1 | 36.5 | 10.3 | 47.4 | 46.3 | 69.4 | | MERT-95M K-Means | 90.6 | 38.4 | 65.0 | 78.6 | 52.9 | 69.9 | 74.6 | 77.2 | | MERT-95M RVQ-VAE | 91.0 | 39.3 | 63.5 | 78.6 | 60.0 | 76.4 | 74.2 | 83.7 | To verify that the benefits brought by the MERT pre-training, we further evaluate the performances of the continuous representation from the encoder of the RVQ-VAE model, as shown in Tab. 6. These supplementary results indicate that the vanilla continuous representations alone are insufficient for a robust music understanding baseline. ## Appendix B Experiment Details ### B.1 Downstream Tasks We evaluate the models on 14 downstream tasks to provide a comprehensive view of our method and the comparison between baselines. The full descriptions of the datasets and tasks are given as follows. Music Tagging involves determining which of a set of fixed tags apply to a particular song. Tag categories may include genre, instrumentation, mood, tempo (e.g. fast) or other tags. We used two large datasets: MagnaTagATune (MTT) (Law et al.,, 2009) and MTG-Jamendo (Bogdanov et al.,, 2019). For both datasets, we limit the tag vocabulary according to official instructions. We use all clips in MTT and MTG-Jamendo. Since many of the audio recordings among 5.5k MTG-Jamendo excerpts are longer than the 30s, we averaged the multiple embeddings computed with a sliding window as the overall embedding. The window length is set to the same default length as in every system. For MERT series, the window length is typically set to 30s. The metrics are the macro-average of ROC-AUCs and the average precision (AP) / PR-AUC among all top-50 tags. Key detection predicts the tonal scale and dominant pitch level of a song. We use Giantsteps (Knees et al.,, 2015) as test set and a commonly-used subset of Giantsteps-MTG-keys dataset (Korzeniowski and Widmer,, 2017) as the training and validation set. The splitting is the same as in (Castellon et al.,, 2021). The metric is a refined accuracy with error tolerance, giving partial credit to reasonable errors (Raffel et al.,, 2014). Genre classification estimates the most appropriate genre for each given song. We report the accuracy of the GTZAN (Tzanetakis and Cook,, 2002) dataset along with ROC and AP on MTG-Genre, since the former task is a multi-class classification and the latter is multi-label. We used the standard ”fail-filtered” split (Kereliuk et al.,, 2015) for GTZAN. Emotion score regression. The Emomusic dataset (Soleymani et al.,, 2013) contains 744 music clips of 45 seconds in length, each reported on a two-dimensional valence-arousal plane after listening, where valence indicates positive and negative emotional responses, and arousal indicates emotional intensity. We use the same dataset split as (Castellon et al.,, 2021). The official evaluation metric is the determination coefficient ( $r^2$ ) between the model regression results and human annotations of arousal (EmoA) and valence (EmoV) (Soleymani et al.,, 2013). For inference, we split the 45-second clip into a 5-second sliding window and averaged the prediction. Instrument classification is the process of identifying which instruments are included in a given sound. We use the Nsynth (Engel et al.,, 2017) and MTG-instrument datasets. The former is a monophonic note-level multi-class task with 306k audio samples in 11 instrument classes with accuracy as an indicator. The latter is a subset of MTG-Jamendo, containing 25k polyphonic audio tracks and 41 instrument tags; each track can contain multiple instruments and is evaluated on ROC and AP. Pitch classification estimates which of the 128 pitch categories the given audio segment belongs to. We use the NSynth dataset for this task. Given these segments are short monophonic audio, this task is multi-class, and the accuracy is used as an evaluation metric. Vocal technique detection involves identifying what singing techniques are contained in a given audio clip. We use the VocalSet dataset (Wilkins et al.,, 2018), which is the only publicly available dataset for the study of singing techniques. The dataset contains the vocals of 20 different professional singers (9 female and 11 male) who perform 17 different singing techniques in various contexts for a total of 10.1 hours. As the audio clips are divided into 3 seconds, the task only requires a judgement on the type of technique and not on the start and end of the technique. We used the same 10 different singing techniques as in Yamamoto et al., (2022) as a subset and used the same 15 singers as the training and validation sets and 5 singers as the test set. Since there is no accepted division between training and validation sets, we selected 9 singers as the training set and 6 singers as the validation set. All the 3-second segments that originate from the same recording are allocated to the same part of the split (e.g. all are in the training set). The evaluation metric is accuracy. Singer identification identifies the vocal performer from a given recording. We use the VocalSet dataset for this task. We randomly divided the dataset into a training set, validation set and testing set based on a ratio of 12:8:5, all containing the same 20 singers. Beat tracking is the process of determining whether there is a beat in each frame of a given piece of music. We use an offline approach to the binary classification, i.e. the model can use information following each frame to help with inference. The model needs to output frame-by-frame predictions at a certain frequency and post-process them using a dynamic Bayesian network (DBN) (Böck et al., 2016b, ) to obtain the final result. The DBN is implemented using madmom (Böck et al., 2016a, ). The dataset we use is GTZAN Rhythm (Marchand and Peeters,, 2015). We also label the two adjacent frames of each label as beat, which is a common way of label smoothing in beat tracking to improve the performance of the model and to compare the SSL model fairly with the spin model. The model is evaluated using the f_measure implemented in mir_eval (Raffel et al.,, 2014), and the prediction is considered correct if the difference between the predicted event and the ground truth does not exceed 20ms. In this task, some models were trained on other datasets, and the full GTZAN set was used as the test set. Source separation. Source separation aims to demix the music recording into its constituent parts, e.g., vocals, drums, bass, and others. We adopt MUSDB18 (Rafii et al.,, 2017), a widely used benchmark dataset in music source separation. MUSDB18 contains 150 full-length music tracks (1̃0 hours), along with multiple isolated stems. We use 86 tracks for training, 14 tracks for validation, and 50 tracks for evaluation following the official setting in MUSDB18. During training, we randomly sample 6-second segments and apply random track mixing for augmentation. Due to the difficulty of this task, we adopt the baseline architecture in the Music Demixing Challenge (MDX) 2021 (Mitsufuji et al.,, 2022), which consists of three linear layers and three bi-directional LSTM layers. We directly compute the l2-loss between predicted and ground-truth spectrograms for optimisation. The metric for this task is the Source-to-Distortion Ratio (SDR) defined by MDX 2021 (Mitsufuji et al.,, 2022), which is the mean across the SDR scores of all songs. ### B.2 Testing Protocol Details Our aim is to explore the generality and standardisation of the framework. We, therefore, freeze the parameters of the pre-trained model to extract pre-trained features as fixed depth embeddings that are fed to each downstream task-specific prediction head. This allows for as lightweight a solution as possible for all tasks, thus testing whether the representations are easily reusable across different downstream tasks. In the following, we first describe the selected pre-trained baseline model, followed by the downstream model and training strategy. In order to detect representations with relevant information about the downstream MIR task, we use these representations as input features to train a shallow supervised model on each task. For most tasks we use an MLP with one hidden layer, and for source separation, we use the baseline of the demixing data challenge described above, with the 3-layer LSTM used as post-processing. Since some representations may require different hyperparameter configurations to be successfully trained, we performed the following hyperparameter search for each mentioned SSL mainly based on MARBLE https://marble-bm.shef.ac.uk benchmark, using the validation set for each downstream task. - Model: {one-layer MLP with 512 hidden units, 3-layer LSTM (source separation only)} - Batch size: {64} - Learning rate: {1e-4, 5e-4, 1e-3, 5e-3, 1e-2} - Dropout probability: {0.25} - Optimizer: Default Adam optimizer - Early Stopping: Fixed across all models with task-specific patience - LR Scheduler: Reduce LR On Plateau, fixed across all models with task-specific patience In addition, although we use the same hyperparameter grid for all tasks, the learning objectives vary from task to task. For the same task with a uniform dataset, if there are different evaluation metrics, we will average the two evaluation metrics. We keep the best validation set results, and use the test set results as the final results of the benchmark. ### B.3 Training Instability In the experiments of scaling up to MERT-330M under mix precision training (fp16), we have explored several settings and plot the gradient norm, scale of loss, the MLM loss on acoustic targets, and the MLM loss on musical targets (see Fig. 2). We first adopt the Pre-LN setting as in the HuBERT (Hsu et al.,, 2021) x-large model for stable training. However, the training crashed around 50K step under this vanilla solution from the speech model and thus we restart the pre-training at 40K step with gradient clipping threshold reduced from $10.0$ to $1.0$ . The second run of Pre-LN lasted for 40K steps and crashed due to the same reason of reaching minimum loss scale. We suspect the instability could be brought by the increased depth of the Transformer module. Following the strategies in DeepNorm (Wang et al., 2022a, ), we tried to alleviate the instability by initialising the Transformer with smaller values and enhancing the residual connection in the Post-LN. Unfortunately, such modification causes model collapse around 20K steps. We then turned back to the stable Pre-LN setting and leveraged the attention relaxation trick proposed in Chen et al., 2021b . The additional scale constant in softmax calculation in the attention module alleviates the overflow problem and allows the final version of MERT-330M model to be trained stably over 100K steps. <details> <summary>x15.png Details</summary>  ### Visual Description ## Line Graph: Gradient Norms During Training ### Overview The line graph displays the gradient norms over training steps for four different normalization techniques: Pre-Norm, Post-Norm, DeepNorm, and Attn. Relax. The gradients are clipped at a maximum value of 10 for Pre-Norm and 1 for the other techniques. ### Components/Axes - **X-axis (Training Step)**: Represents the number of training steps, ranging from 0 to 100,000. - **Y-axis (Gradient Norm)**: Represents the gradient norm values, ranging from 0 to 30. - **Legend**: Contains four lines, each representing a different normalization technique. - **Pre-Norm | Gradient Clip=10 | Run 1**: Blue line with circular markers. - **Pre-Norm | Gradient Clip=1 | Run 2**: Orange line with circular markers. - **Post-Norm | DeepNorm | Gradient Clip=1**: Green line with square markers. - **Pre-Norm | Attn. Relax | Gradient Clip=1**: Pink line with square markers. ### Detailed Analysis - **Pre-Norm Techniques**: Both Pre-Norm techniques with Gradient Clip=10 and Gradient Clip=1 show a similar trend, with a sharp increase in gradient norm around the 20,000 training step mark, followed by a gradual decrease. - **Post-Norm Technique**: The Post-Norm technique with DeepNorm and Gradient Clip=1 shows a more stable gradient norm, with a slight increase around the 20,000 training step mark and a gradual decrease thereafter. - **Attn. Relax Technique**: The Attn. Relax technique with Gradient Clip=1 shows a similar trend to Pre-Norm techniques, with a sharp increase around the 20,000 training step mark, followed by a gradual decrease. ### Interpretation The data suggests that the normalization techniques have different effects on the gradient norms during training. The Pre-Norm techniques with Gradient Clip=10 and Gradient Clip=1 show a similar trend, with a sharp increase in gradient norm around the 20,000 training step mark, followed by a gradual decrease. This could indicate that the normalization techniques are not significantly affecting the gradient norms during the later stages of training. The Post-Norm technique with DeepNorm and Gradient Clip=1 shows a more stable gradient norm, with a slight increase around the 20,000 training step mark and a gradual decrease thereafter. This could indicate that the normalization techniques are having a more significant effect on the gradient norms during the later stages of training. The Attn. Relax technique with Gradient Clip=1 shows a similar trend to Pre-Norm techniques, with a sharp increase around the 20,000 training step mark, followed by a gradual decrease. This could indicate that the normalization techniques are not significantly affecting the gradient norms during the later stages of training. Overall, the data suggests that the normalization techniques have different effects on the gradient norms during training, with the Post-Norm technique with DeepNorm and Gradient Clip=1 showing a more stable gradient norm. </details> (a) Gradient Norm <details> <summary>x16.png Details</summary>  ### Visual Description ## Line Graph: Training Loss Comparison ### Overview The line graph shows the training loss over 100,000 steps for four different models: Pre-Norm, Pre-Norm with Gradient Clip=1, Post-Norm with DeepNorm and Gradient Clip=1, and Pre-Norm with Attention Relax and Gradient Clip=1. The loss scale is on the y-axis, ranging from 0.00 to 2.00, and the training step is on the x-axis. ### Components/Axes - **Y-axis**: Loss Scale, ranging from 0.00 to 2.00. - **X-axis**: Training Step, ranging from 0K to 100K. - **Legend**: Four lines, each representing a different model. - **Pre-Norm | Gradient Clip=10 | Run 1**: Blue line with small markers. - **Pre-Norm | Gradient Clip=1 | Run 2**: Orange line with small markers. - **Post-Norm | DeepNorm | Gradient Clip=1**: Green line with small markers. - **Pre-Norm | Attention Relax | Gradient Clip=1**: Pink line with small markers. ### Detailed Analysis - **Pre-Norm with Gradient Clip=10**: Shows a sharp increase in loss at the beginning, followed by a gradual decline. - **Pre-Norm with Gradient Clip=1**: Exhibits a more stable loss pattern with minor fluctuations. - **Post-Norm with DeepNorm**: Displays a consistent loss pattern with slight variations. - **Pre-Norm with Attention Relax**: Shows a similar trend to Pre-Norm with Gradient Clip=1, with a slight increase in loss at the beginning. ### Key Observations - **Pre-Norm with Gradient Clip=10** has the highest loss at the beginning, indicating a potential issue with the model's initial training. - **Pre-Norm with Gradient Clip=1** and **Pre-Norm with Attention Relax** show more stable loss patterns. - **Post-Norm with DeepNorm** maintains a consistent loss pattern with minor fluctuations. ### Interpretation The data suggests that the Pre-Norm model with Gradient Clip=10 may be overfitting or experiencing instability during training. The Pre-Norm models with Gradient Clip=1 and Attention Relax show more stable performance, indicating that these models may be better suited for the task at hand. The Post-Norm model with DeepNorm also performs well, suggesting that normalization techniques can be beneficial for the model's training. </details> (b) Loss Scale <details> <summary>x17.png Details</summary>  ### Visual Description ## Acoustic Loss on Codebook-0 ### Overview The graph shows the acoustic loss over training steps for different configurations of a model on the Codebook-0 dataset. The loss is measured in decibels (dB) and is plotted against the number of training steps. ### Components/Axes - **Y-axis**: Acoustic Loss in dB - **X-axis**: Training Step - **Legend**: Different configurations of the model with their respective settings (e.g., Pre-Norm, Gradient Clip, Run 1, etc.) ### Detailed Analysis or ### Content Details - **Pre-Norm**: The loss decreases sharply at the beginning of training and then stabilizes. - **Gradient Clip=10**: Similar to Pre-Norm, but with a slightly higher initial loss. - **Post-Norm**: Shows a more gradual decrease in loss. - **DeepNorm**: The loss decreases more steeply than Post-Norm. - **Attn. Relax**: The loss decreases the most, indicating the best performance among the configurations. ### Key Observations - **Pre-Norm and Gradient Clip=10**: Show the highest loss, indicating the worst performance. - **Post-Norm and DeepNorm**: Show moderate loss, indicating good performance. - **Attn. Relax**: Shows the lowest loss, indicating the best performance. ### Interpretation The data suggests that the model's performance is significantly affected by the normalization technique used. The "Attn. Relax" configuration, which likely includes attention mechanisms and relaxation techniques, results in the lowest loss, indicating the best performance. The "Pre-Norm" and "Gradient Clip=10" configurations show the highest loss, indicating the worst performance. The "Post-Norm" and "DeepNorm" configurations show moderate performance. The graph provides insights into the effectiveness of different normalization techniques in improving the model's performance on the Codebook-0 dataset. </details> (c) Acoustic MLM Loss on Codebook-0 <details> <summary>x18.png Details</summary>  ### Visual Description ## Line Chart: Training Loss ### Overview The line chart displays the training loss of a model over 100,000 training steps. The loss is measured in terms of Musical Loss, which is a metric used to evaluate the performance of a model in generating musical sequences. ### Components/Axes - **X-axis (Training Step)**: Represents the number of training steps, ranging from 0 to 100,000. - **Y-axis (Musical Loss)**: Represents the loss value, ranging from 0 to 1.4. - **Legend**: Contains four lines, each representing a different training method or configuration. - **Pre-Norm | Gradient Clip=10 | Run 1**: Blue line with a gradient clip of 10. - **Pre-Norm | Gradient Clip=1 | Run 2**: Orange line with a gradient clip of 1. - **Post-Norm | DeepNorm | Gradient Clip=1**: Green line with deep normalization and a gradient clip of 1. - **Pre-Norm | Attn. Relax | Gradient Clip=1**: Pink line with attention relaxation and a gradient clip of 1. ### Detailed Analysis - The **Pre-Norm** methods (blue and orange lines) show a significant decrease in loss initially, but the loss plateaus after a few thousand steps. - The **Post-Norm** method (green line) shows a more gradual decrease in loss, which then stabilizes. - The **Pre-Norm | Attn. Relax** method (pink line) shows a similar trend to the **Pre-Norm | Gradient Clip=10** method, with a slight plateau after the initial decrease. ### Key Observations - The **Post-Norm** method consistently shows the lowest loss throughout the training process. - The **Pre-Norm** methods show a similar trend, with the **Pre-Norm | Gradient Clip=10** method having a slightly lower loss than the **Pre-Norm | Gradient Clip=1** method. - The **Pre-Norm | Attn. Relax** method shows a similar trend to the **Pre-Norm | Gradient Clip=10** method, with a slight plateau after the initial decrease. </details> (d) Music MLM Loss Figure 2: Illustration of the Training Curves of Trials on Large (330M) Models. Only the acoustic MLM loss on codebook 0 in the RVQ-VAE is shown as the other seven show similar trends. ## Appendix C Representation Visualisation We select two of our checkpoints, MERT-95M-public K-means and MERT-330M RVQ-VAE, and visualise the GTZAN representations with genre annotation shown in Fig. 3, Fig. 4, Fig. 5 and Fig. 6. The top 6 and top 8 transformer output layers are used in the visualisation for MERT-95M-public K-means and MERT-330M RVQ-VAE, correspondingly. The dimension reduction is achieved by the Uniform Manifold Approximation and Projection (UMAP) https://github.com/lmcinnes/umap, whereas the representations from the training set are used to learn the dimension reduction mapping. We observe that representations from both of the checkpoints present a pattern of clustering according to the genre information under different layer settings. Interestingly, the representations from the higher layers do not necessarily show stronger genre-based clustering tendency, which suggests that 1) genre may not be the most abstractive labels for these music examples or 2) the top transformer layers focus more on the MLM pre-training objectives. <details> <summary>x19.png Details</summary>  ### Visual Description ## Scatter Plot: Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across two sets: the "Valid Set" and the "Test Set." Each genre is represented by a different color, and the size of each dot corresponds to the number of tracks in that genre within the respective set. ### Components/Axes - **X-axis**: Represents the number of tracks in each genre. - **Y-axis**: Represents the genre itself. - **Legend**: Color-coded to match the genres with their respective colors. - **Title**: "Genre Distribution" ### Detailed Analysis - **Valid Set**: The dots are more densely packed, indicating a higher concentration of tracks in each genre. - **Test Set**: The dots are more spread out, suggesting a more diverse distribution of genres. ### Key Observations - **Blues**: The largest number of tracks, with a significant presence in both sets. - **Rock**: The second-largest number of tracks, with a notable presence in both sets. - **Pop**: A moderate number of tracks, with a consistent presence in both sets. - **Jazz**: A moderate number of tracks, with a consistent presence in both sets. - **Country**: A moderate number of tracks, with a consistent presence in both sets. - **Hip Hop**: A moderate number of tracks, with a consistent presence in both sets. - **Disco**: A moderate number of tracks, with a consistent presence in both sets. - **Metal**: A moderate number of tracks, with a consistent presence in both sets. - **Reggae**: A moderate number of tracks, with a consistent presence in both sets. - **Classical**: A moderate number of tracks, with a consistent presence in both sets. ### Interpretation The scatter plot suggests that the genres are distributed more evenly across the two sets, with no single genre dominating either set. The larger number of tracks in the "Valid Set" compared to the "Test Set" could indicate a more curated or representative sample of the genres. The consistent presence of genres across both sets suggests that the genres are well-represented in the dataset. The moderate number of tracks in each genre indicates that the dataset is not overly biased towards any particular genre. </details> (a) MERT-95M-public K-means Transformer Layer 7 Representations of GTZAN. <details> <summary>x20.png Details</summary>  ### Visual Description ## Scatter Plot: Distribution of Music Genres ### Overview The scatter plot displays the distribution of various music genres across two sets: the "Valid Set" and the "Test Set." Each genre is represented by a different color, and the size of each dot corresponds to the number of tracks in that genre. ### Components/Axes - **X-axis**: Represents the number of tracks in each genre. - **Y-axis**: Represents the genre itself. - **Legend**: Color-coded legend indicating the different music genres. - **Title**: "Valid Set" and "Test Set" labels. ### Detailed Analysis or Content Details - **Valid Set**: The dots are more densely packed, indicating a higher concentration of tracks in certain genres. - **Test Set**: The dots are more spread out, suggesting a more diverse distribution of tracks across genres. ### Key Observations - **Blues**: The largest cluster of dots, indicating a high number of tracks. - **Rock**: The second-largest cluster, followed by Blues. - **Disco**: A moderate number of tracks. - **Jazz**: A moderate number of tracks. - **Country**: A moderate number of tracks. - **Pop**: A moderate number of tracks. - **Metal**: A moderate number of tracks. - **Hip Hop**: A moderate number of tracks. - **Reggae**: A moderate number of tracks. - **Classical**: A moderate number of tracks. ### Interpretation The scatter plot suggests that the music genres are distributed differently between the "Valid Set" and the "Test Set." The "Valid Set" shows a more concentrated distribution, particularly for Blues, while the "Test Set" shows a more diverse distribution. This could indicate that the "Valid Set" is a more representative sample of the music genres, or that the "Test Set" is a more diverse sample. The data does not provide information on the specific characteristics of the tracks within each genre, such as tempo, genre-specific features, or artist popularity. </details> (b) MERT-95M-public K-means Transformer Layer 8 Representations of GTZAN. <details> <summary>x21.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across a dataset. The plot is divided into two sections: the "Valid Set" and the "Test Set," each representing a different subset of the data. ### Components/Axes - **X-axis**: Represents the number of data points for each genre. - **Y-axis**: Represents the number of data points for each genre. - **Legend**: Color-coded to represent different music genres. - **Data Points**: Each point represents a single data entry, with its position determined by the genre it belongs to. ### Detailed Analysis - **Valid Set**: The data points are more densely packed, indicating a higher concentration of data points for each genre. - **Test Set**: The data points are more spread out, suggesting a lower concentration of data points for each genre. ### Key Observations - **Blues**: The highest concentration of data points, indicating a large number of entries for this genre. - **Rock**: The second highest concentration, followed by blues. - **Pop**: The third highest concentration, with a moderate number of entries. - **Jazz**: The fourth highest concentration, with a moderate number of entries. - **Disco**: The fifth highest concentration, with a moderate number of entries. - **Hip Hop**: The sixth highest concentration, with a moderate number of entries. - **Country**: The seventh highest concentration, with a moderate number of entries. - **Metal**: The eighth highest concentration, with a moderate number of entries. - **Reggae**: The ninth highest concentration, with a moderate number of entries. - **Classical**: The lowest concentration of data points, indicating a smaller number of entries for this genre. ### Interpretation The scatter plot suggests that the majority of the data points are concentrated in the genres of blues, rock, and pop. This indicates that these genres are more prevalent in the dataset. The spread out data points in the test set suggest that the model used to classify the genres may not be as accurate for genres that are less represented in the dataset. The high concentration of data points for blues and rock also suggests that these genres are more common in the dataset than the other genres. Overall, the scatter plot provides a visual representation of the distribution of music genres in the dataset. </details> (c) MERT-95M-public K-means Transformer Layer 9 Representations of GTZAN. Figure 3: Illustration of the MERT-95M-public K-means Layer 7 to 9 Pre-trained Representations. <details> <summary>x22.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across two sets: the "Valid Set" and the "Test Set." Each genre is represented by a different color, and the size of each dot corresponds to the number of tracks in that genre within the respective set. ### Components/Axes - **X-axis**: Represents the number of tracks in each genre. - **Y-axis**: Represents the genre itself. - **Legend**: Located on the left side, it maps the colors to the corresponding genres. - **Title**: "Valid Set" and "Test Set" are labeled at the top of each subplot. ### Detailed Analysis - **Valid Set**: The dots are more densely packed, indicating a higher concentration of tracks in each genre. The genres with the highest number of tracks are "blues" and "rock." - **Test Set**: The dots are more spread out, suggesting a more diverse distribution of genres. The genres with the highest number of tracks are "pop" and "reggae." ### Key Observations - **Genre Diversity**: The "Test Set" shows a wider variety of genres compared to the "Valid Set." - **Track Concentration**: The "Valid Set" has a more concentrated distribution of tracks, while the "Test Set" has a more even distribution. ### Interpretation The scatter plot suggests that the "Valid Set" is a more representative sample of the music genre distribution, with a higher concentration of tracks in specific genres. The "Test Set," while more diverse, may not be as representative due to the more even distribution of genres. This could indicate that the "Valid Set" is a more controlled and curated sample, possibly used for training a model, while the "Test Set" is used for evaluating the model's performance on a more diverse set of data. </details> (a) MERT-95M-public K-means Transformer Layer 10 Representations of GTZAN. <details> <summary>x23.png Details</summary>  ### Visual Description ## Scatter Plot: Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across a dataset. The plot is divided into two sections: the "Valid Set" on the left and the "Test Set" on the right. Each section contains a collection of colored dots, representing individual music genres. ### Components/Axes - **X-axis**: Represents the genre categories, with labels such as blues, classical, country, disco, hip hop, jazz, metal, pop, reggae, and rock. - **Y-axis**: Not explicitly labeled, but it likely represents another dimension of the data, possibly related to the popularity or frequency of each genre. - **Legend**: Located on the left side of the plot, it matches the colors of the dots to their corresponding genres. - **Data Points**: Each dot represents a single music genre, with its position on the plot indicating its distribution across the two sets. ### Detailed Analysis - **Valid Set**: The dots in this section are more densely packed, indicating a higher concentration of genres within this set. - **Test Set**: The dots are more spread out, suggesting a more diverse distribution of genres in this set. ### Key Observations - **Blues**: Appears to be a common genre in both sets. - **Rock**: Also present in both sets, but in smaller numbers compared to blues. - **Disco**: More prevalent in the test set. - **Hip Hop**: More prevalent in the valid set. - **Jazz**: More prevalent in the test set. - **Metal**: More prevalent in the valid set. - **Pop**: More prevalent in the test set. - **Reggae**: More prevalent in the valid set. ### Interpretation The scatter plot suggests that the genres are distributed differently between the valid and test sets. The genres that are more prevalent in the valid set, such as blues, rock, and jazz, are also more prevalent in the test set. Conversely, genres like disco, hip hop, and reggae are more prevalent in the test set. This could indicate that the genres are more consistent in the valid set, while the test set may have a more diverse or less consistent distribution. The presence of outliers, such as genres that are not represented in the test set, could suggest that these genres are less common or less represented in the dataset. </details> (b) MERT-95M-public K-means Transformer Layer 11 Representations of GTZAN. <details> <summary>x24.png Details</summary>  ### Visual Description ## Scatter Plot: Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across a dataset. The plot is divided into two sections: the "Valid Set" and the "Test Set," each containing a different number of data points. ### Components/Axes - **X-axis**: Represents the genre categories, including blues, classical, country, disco, hip hop, jazz, metal, pop, reggae, and rock. - **Y-axis**: Represents the number of data points for each genre. - **Legend**: Located on the left side of the plot, it matches the colors of the data points to their respective genres. - **Data Points**: Each point represents a single data entry, with its position determined by the genre and the number of data points. ### Detailed Analysis or Content Details - **Valid Set**: Contains 100 data points, with a more even distribution across all genres. - **Test Set**: Contains 50 data points, with a slightly higher concentration of data points in the hip hop and jazz genres. ### Key Observations - The genres are well-represented in both sets, with no single genre dominating either. - The hip hop and jazz genres have a higher number of data points in the test set compared to the valid set. - The distribution of data points is relatively even across all genres in the valid set, but there is a slight skew towards the hip hop and jazz genres in the test set. ### Interpretation The scatter plot suggests that the dataset is balanced in terms of genre representation, with no single genre having a disproportionate number of data points. The slight skew towards hip hop and jazz in the test set could indicate that these genres are more prevalent or have a higher impact in the dataset. This information could be useful for further analysis or for understanding the characteristics of the dataset. </details> (c) MERT-95M-public K-means Transformer Layer 12 Representations of GTZAN. Figure 4: Illustration of the MERT-95M-public K-means Layer 10 to 12 Pre-trained Representations. <details> <summary>x25.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across two sets: the "Valid Set" and the "Test Set." Each genre is represented by a different color, and the size of each dot corresponds to the number of tracks associated with that genre. ### Components/Axes - **X-axis**: Represents the number of tracks. - **Y-axis**: Represents the genre. - **Legend**: Color-coded legend indicating the genres. - **Title**: "Valid Set" and "Test Set" labels. ### Detailed Analysis - **Valid Set**: The dots are more densely packed, indicating a higher concentration of tracks for each genre. - **Test Set**: The dots are more spread out, suggesting a more diverse distribution of tracks across genres. ### Key Observations - **Blues**: The highest number of tracks, with a significant concentration in the "Valid Set." - **Rock**: The second highest number of tracks, with a moderate concentration in both sets. - **Pop**: The third highest number of tracks, with a moderate concentration in both sets. - **Jazz**: The fourth highest number of tracks, with a moderate concentration in both sets. - **Country**: The fifth highest number of tracks, with a moderate concentration in both sets. - **Disco**: The sixth highest number of tracks, with a moderate concentration in both sets. - **Hip Hop**: The seventh highest number of tracks, with a moderate concentration in both sets. - **Metal**: The eighth highest number of tracks, with a moderate concentration in both sets. - **Reggae**: The ninth highest number of tracks, with a moderate concentration in both sets. - **Classical**: The tenth highest number of tracks, with a moderate concentration in both sets. ### Interpretation The scatter plot suggests that the genres are distributed more evenly across the two sets, with no single genre dominating either set. The "Valid Set" shows a higher concentration of tracks for each genre, which could indicate a more curated or well-represented dataset. The "Test Set" shows a more diverse distribution, which could suggest that the dataset is more representative of the real-world music landscape. The even distribution across genres in both sets implies that the model used to generate the data is robust and can generalize well to new data. </details> (a) MERT-330M RVQ-VAE Transformer Layer 17 Representations of GTZAN. <details> <summary>x26.png Details</summary>  ### Visual Description ## Scatter Plot: Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across a two-dimensional space. Each point represents a genre, with its position determined by its characteristics. The plot is divided into two sections: the "Valid Set" and the "Test Set," indicating the separation of training and testing data. ### Components/Axes - **X-axis**: Represents the characteristic of one genre, such as tempo or key signature. - **Y-axis**: Represents the characteristic of another genre, such as genre popularity or genre type. - **Legend**: Color-coded to differentiate between genres, with each color corresponding to a specific genre. - **Data Points**: Each point on the plot represents a genre, with its position determined by its characteristics. ### Detailed Analysis or Content Details - **Valid Set**: The data points in this section are clustered together, indicating a strong correlation between the characteristics and the genre. - **Test Set**: The data points in this section are more spread out, suggesting that the model's predictions are less accurate when applied to new, unseen data. ### Key Observations - **Clusters**: There are distinct clusters of data points, each representing a different genre. - **Outliers**: Some data points are isolated from the main clusters, indicating that these genres may have unique characteristics not captured by the model. - **Trends**: The overall trend shows that genres with similar characteristics tend to cluster together. ### Interpretation The scatter plot suggests that the model used to classify music genres is effective in distinguishing between genres with similar characteristics. However, the spread of data points in the test set indicates that the model may not generalize well to new data. This could be due to overfitting to the training data or the model's inability to capture all the nuances of the genres. The presence of outliers suggests that there are genres with unique characteristics that may not be accurately represented by the model. </details> (b) MERT-330M RVQ-VAE Transformer Layer 18 Representations of GTZAN. <details> <summary>x27.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across different data sets. The genres are represented by different colors, and the data points are scattered across the plot to show the spread and clustering of each genre. ### Components/Axes - **X-axis**: Represents the range of values for one variable, likely the popularity or frequency of the genre. - **Y-axis**: Represents the range of values for another variable, likely the diversity or variety of the genre. - **Legend**: Located on the left side of the plot, it associates each color with a specific music genre. - **Data Points**: Each point on the plot corresponds to a music genre and is colored according to the legend. ### Detailed Analysis or Content Details - **Valid Set**: The data points in the "Valid Set" are more densely clustered, indicating a higher concentration of certain genres. - **Test Set**: The "Test Set" shows a more dispersed distribution of genres, suggesting a broader range of musical styles. ### Key Observations - **Clusters**: There are distinct clusters of genres, such as blues, jazz, and rock, which are more concentrated in the "Valid Set". - **Outliers**: Some genres, like disco and hip-hop, are more spread out in the "Test Set". - **Trends**: The overall trend shows a higher concentration of certain genres in the "Valid Set" compared to the "Test Set". ### Interpretation The scatter plot suggests that the genres with higher popularity or frequency are more concentrated in the "Valid Set", indicating a more reliable or representative sample. The "Test Set" shows a broader range of genres, which could imply that the data is more diverse or that the "Test Set" is a smaller or less representative sample. The presence of outliers in the "Test Set" suggests variability in the data that may not be present in the "Valid Set". </details> (c) MERT-330M RVQ-VAE Transformer Layer 19 Representations of GTZAN. <details> <summary>x28.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across a dataset. Each genre is represented by a different color, and the points are plotted on a two-dimensional plane with the x-axis representing one feature and the y-axis representing another feature. ### Components/Axes - **X-axis**: Represents one feature, possibly the tempo or energy level of the music. - **Y-axis**: Represents another feature, possibly the complexity or emotional intensity of the music. - **Legend**: Color-coded legend indicating the different music genres. - **Data Points**: Each point represents a single music genre, with its color corresponding to the legend. ### Detailed Analysis or ### Content Details - **Genres**: The genres included are blues, classical, country, disco, hip hop, jazz, metal, pop, reggae, and rock. - **Distribution**: The data points are spread across the plot, with no clear clustering of genres. - **Trends**: There is no clear trend or pattern in the distribution of genres, suggesting that the features used to plot the data do not have a strong correlation with the genre classification. ### Key Observations - **Variability**: There is significant variability in the distribution of genres, indicating that the features used to plot the data do not strongly differentiate between genres. - **Outliers**: There are no outliers in the data, suggesting that the dataset is relatively balanced in terms of genre representation. ### Interpretation The scatter plot suggests that the features used to plot the data do not have a strong correlation with the genre classification. This could indicate that the dataset is not well-suited for genre classification or that the features used are not informative enough to distinguish between genres. The lack of clustering and the variability in the distribution of genres suggest that the dataset may need to be preprocessed or that the features used need to be re-evaluated. </details> (d) MERT-330M RVQ-VAE Transformer Layer 20 Representations of GTZAN. Figure 5: Illustration of the MERT-330M RVQ-VAE Layer 17 to 20 Pre-trained Representations. <details> <summary>x29.png Details</summary>  ### Visual Description ## Scatter Plot: Genre Distribution ### Overview The scatter plot displays the distribution of different music genres across a dataset. The genres are represented by colored dots, and the x-axis and y-axis likely represent some form of quantitative measure related to each genre. ### Components/Axes - **X-Axis**: Likely represents a quantitative measure such as popularity, frequency, or another relevant metric. - **Y-Axis**: Likely represents another quantitative measure such as genre type, popularity, or another relevant metric. - **Legend**: Color-coded legend indicating the different genres (e.g., blues, classical, country, etc.). - **Title**: "Genre Distribution" indicating the purpose of the plot. ### Detailed Analysis or Content Details - **Blues**: Dotted in blue, located towards the lower left quadrant. - **Classical**: Dotted in red, located towards the upper left quadrant. - **Country**: Dotted in green, located towards the lower right quadrant. - **Disco**: Dotted in purple, located towards the upper right quadrant. - **Hip Hop**: Dotted in orange, located towards the center. - **Jazz**: Dotted in brown, located towards the lower right quadrant. - **Metal**: Dotted in pink, located towards the upper right quadrant. - **Pop**: Dotted in yellow, located towards the center. - **Reggae**: Dotted in teal, located towards the lower right quadrant. - **Rock**: Dotted in light blue, located towards the upper left quadrant. ### Key Observations - **Blues and Country** are more concentrated towards the lower left quadrant. - **Disco and Hip Hop** are more concentrated towards the upper right quadrant. - **Jazz and Reggae** are more concentrated towards the lower right quadrant. - **Pop** is more concentrated towards the center. - There is a noticeable spread of genres across the plot, indicating a diverse dataset. ### Interpretation The scatter plot suggests that the dataset contains a wide range of music genres, with some genres being more popular or frequent than others. The concentration of certain genres in specific quadrants might indicate a trend or a characteristic of the data. For example, the higher concentration of blues and country towards the lower left quadrant might suggest that these genres are more prevalent in the lower left segment of the dataset. The overall distribution indicates a diverse and possibly balanced dataset with no single genre dominating the plot. </details> (a) MERT-330M RVQ-VAE Transformer Layer 21 Representations of GTZAN. <details> <summary>x30.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across two sets: the "Valid Set" and the "Test Set." Each genre is represented by a different color, and the size of the circle indicates the frequency of that genre within the respective set. ### Components/Axes - **X-axis**: Represents the frequency of each music genre. - **Y-axis**: Represents the number of data points for each genre. - **Legend**: Color-coded legend indicating the different music genres. - **Data Points**: Each point represents a single music genre. ### Detailed Analysis - **Valid Set**: The points are more concentrated towards the center of the plot, indicating a higher frequency of genres like pop, rock, and jazz. - **Test Set**: The points are more spread out, suggesting a more diverse distribution of genres. ### Key Observations - **Genre Distribution**: The genres are more evenly distributed in the Test Set compared to the Valid Set. - **Frequency**: The genre with the highest frequency in the Valid Set is jazz, while the genre with the highest frequency in the Test Set is rock. - **Outliers**: There are no significant outliers in either set. ### Interpretation The scatter plot suggests that the genres are more evenly distributed in the Test Set than in the Valid Set. This could indicate that the genres are more diverse in the Test Set, or that the distribution of genres is more consistent across both sets. The higher frequency of jazz in the Valid Set and rock in the Test Set could suggest that these genres are more prevalent in the Test Set. The lack of significant outliers indicates that the data is reliable and consistent. </details> (b) MERT-330M RVQ-VAE Transformer Layer 22 Representations of GTZAN. <details> <summary>x31.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genre Distribution ### Overview The scatter plot displays the distribution of various music genres across two sets: the "Valid Set" and the "Test Set." Each genre is represented by a different color, and the data points are plotted on a two-dimensional plane. ### Components/Axes - **X-axis**: Represents the number of data points for each genre. - **Y-axis**: Represents the number of data points for each genre. - **Legend**: Located on the left side of the plot, it maps the colors to the corresponding genres. - **Data Points**: Each point represents a single genre, with its position determined by the number of data points in that genre. ### Detailed Analysis - **Valid Set**: The data points are more densely packed, indicating a higher concentration of genres in this set. - **Test Set**: The data points are more spread out, suggesting a lower concentration of genres in this set. ### Key Observations - **Blues**: The highest number of data points, indicating a strong presence in the Valid Set. - **Rock**: The second highest number of data points, also present in the Valid Set. - **Disco**: Present in both sets, but with fewer data points than Blues and Rock. - **Jazz**: Present in both sets, but with fewer data points than Blues and Rock. - **Pop**: Present in both sets, but with fewer data points than Blues and Rock. - **Country**: Present in both sets, but with fewer data points than Blues and Rock. - **Metal**: Present in both sets, but with fewer data points than Blues and Rock. - **Hip Hop**: Present in both sets, but with fewer data points than Blues and Rock. - **Reggae**: Present in both sets, but with fewer data points than Blues and Rock. - **Classical**: Present in both sets, but with fewer data points than Blues and Rock. ### Interpretation The scatter plot suggests that the "Valid Set" has a more diverse distribution of music genres compared to the "Test Set." This could indicate that the "Valid Set" is a more representative sample of the music genre distribution. The "Test Set" may have been used to evaluate the performance of a model or algorithm in predicting genre distribution. The presence of fewer data points for some genres in the "Test Set" could suggest that the model is less accurate in predicting the genre distribution for those genres. </details> (c) MERT-330M RVQ-VAE Transformer Layer 23 Representations of GTZAN. <details> <summary>x32.png Details</summary>  ### Visual Description ## Scatter Plot: Music Genres ### Overview The scatter plot displays the distribution of various music genres across different dimensions. The plot is divided into two sections: the "Valid Set" and the "Test Set," each containing a different set of data points. ### Components/Axes - **X-axis**: Represents the dimension of the first feature. - **Y-axis**: Represents the dimension of the second feature. - **Legend**: Color-coded to represent different music genres. - **Data Points**: Each point corresponds to a specific music genre. ### Detailed Analysis or Content Details - **Valid Set**: The data points in the "Valid Set" are more clustered and show a clearer separation between genres. - **Test Set**: The data points in the "Test Set" are more scattered and show less clear separation between genres. ### Key Observations - **Clusters**: There are distinct clusters of data points for each genre in the "Valid Set." - **Scatter**: The "Test Set" shows a more random distribution of data points. - **Color Coding**: The legend uses different colors to represent each genre, which helps in distinguishing between them. ### Interpretation The scatter plot suggests that the music genres are distributed across two different dimensions. The "Valid Set" shows a more organized distribution, indicating that the model used to generate the data is more accurate for the training data. The "Test Set" shows a more random distribution, indicating that the model may not generalize well to new data. The color coding in the legend helps in identifying each genre, which is useful for further analysis and interpretation of the data. </details> (d) MERT-330M RVQ-VAE Transformer Layer 24 Representations of GTZAN. Figure 6: Illustration of the MERT-330M RVQ-VAE Layer 21 to 24 Pre-trained Representations. ## Appendix D Ethics We have taken great care to ensure that our research adheres to ethical principles and guidelines in the codes of conduct. Specifically, we have not used personal user information in the experiments. Audio recordings are collected from open-access streaming services and open-source datasets, where the quality of the recordings varies among 16KHz, 24KHz, and 48KHz. The audio data would not be hosted and distributed. We believe that our work has the potential to contribute to positive social and scientific outcomes regarding the research of automatic music understanding.