Recent state-of-the-art neural audio compression models have progressively adopted residual vector quantization (RVQ). Despite this success, these models employ a fixed number of codebooks per frame, which can be suboptimal in terms of rate-distortion tradeoff, particularly in scenarios with simple input audio, such as silence. To address this limitation, we propose variable bitrate RVQ (VRVQ) for audio codecs, which allows for more efficient coding by adapting the number of codebooks used per frame. Furthermore, we propose a gradient estimation method for the non-differentiable masking operation that transforms from the importance map to the binary importance mask, improving model training via a straight-through estimator. We demonstrate that the proposed training framework achieves superior results compared to the baseline method and shows further improvement when applied to the current state-of-the-art codec. Audio samples are available at: https://yoongi43.github.io/VBRRVQ.github.io/

Binaural audio generation (BAG) aims to convert monaural audio to stereo audio using visual prompts, requiring a deep understanding of spatial and semantic information. The success of the BAG systems depends on the effectiveness of cross-modal reasoning and spatial understanding. Current methods have explored the use of visual information as guidance for binaural audio generation. However, they rely solely on cross-attention mechanisms to guide the generation process and under-utilise the temporal and spatial information in video data during training and inference. These limitations result in the loss of fine-grained spatial details and risk overfitting to specific environments, ultimately constraining model performance. In this paper, we address the aforementioned issues by introducing a new audio-visual binaural generation model with an audio-visual conditional normalisation layer that dynamically aligns the target difference audio features using visual context. To enhance spatial sensitivity, we also introduce a contrastive learning method that mines negatives from shuffled visual features. We also introduce a cost-efficient way to utilise test-time augmentation in video data to enhance performance. Our approach achieves state-of-the-art generation accuracy on the FAIR-Play, MUSIC-Stereo, and YT-MUSIC benchmarks. Code is available at https://github.com/SonyResearch/CCStereo.

This paper presents a new method of singing voice analysis that performs mutually-dependent singing voice separation and vocal fundamental frequency (F0) estimation. Vocal F0 estimation is considered to become easier if singing voices can be separated from a music audio signal, and vocal F0 contours are useful for singing voice separation. This calls for an approach that improves the performance of each of these tasks by using the results of the other. The proposed method first performs robust principal component analysis (RPCA) for roughly extracting singing voices from a target music audio signal. The F0 contour of the main melody is then estimated from the separated singing voices by finding the optimal temporal path over an F0 saliency spectrogram. Finally, the singing voices are separated again more accurately by combining a conventional time-frequency mask given by RPCA with another mask that passes only the harmonic structures of the estimated F0s. Experimental results showed that the proposed method significantly improved the performances of both singing voice separation and vocal F0 estimation. The proposed method also outperformed all the other methods of singing voice separation submitted to an international music analysis competition called MIREX 2014.

This paper presents a novel framework that improves both vocal fundamental frequency (F0) estimation and singing voice separation by making effective use of the mutual dependency of those two tasks. A typical approach to singing voice separation is to estimate the vocal F0 contour from a target music signal and then extract the singing voice by using a time-frequency mask that passes only the harmonic components of the vocal F0s and overtones. Vocal F0 estimation, on the contrary, is considered to become easier if only the singing voice can be extracted accurately from the target signal. Such mutual dependency has scarcely been focused on in most conventional studies. To overcome this limitation, our framework alternates those two tasks while using the results of each in the other. More specifically, we first extract the singing voice by using robust principal component analysis (RPCA). The F0 contour is then estimated from the separated singing voice by finding the optimal path over a F0-saliency spectrogram based on subharmonic summation (SHS). This enables us to improve singing voice separation by combining a time-frequency mask based on RPCA with a mask based on harmonic structures. Experimental results obtained when we used the proposed technique to directly edit vocal F0s in popular-music audio signals showed that it significantly improved both vocal F0 estimation and singing voice separation.

This paper presents an audio-visual beat-tracking method for an entertainment robot that can dance in synchronization with music and human dancers. Conventional music robots have focused on either music audio signals or dancing movements of humans for detecting and predicting beat times in real time. Since a robot needs to record music audio signals by using its own microphones, however, the signals are severely contaminated with loud environmental noise and reverberant sounds. Moreover, it is difficult to visually detect beat times from real complicated dancing movements that exhibit weaker repetitive characteristics than music audio signals do. To solve these problems, we propose a state-space model that integrates both audio and visual information in a probabilistic manner. At each frame, the method extracts acoustic features (audio tempos and onset likelihoods) from music audio signals and extracts skeleton features from movements of a human dancer. The current tempo and the next beat time are then estimated from those observed features by using a particle filter. Experimental results showed that the proposed multi-modal method using a depth sensor (Kinect) for extracting skeleton features outperformed conventional mono-modal methods by 0.20 (F measure) in terms of beat-tracking accuracy in a noisy and reverberant environment.

A method for transcribing vocal expressions such as vibrato, glissando, and kobushi separately from polyphonic music is described. The expressions appear as fluctuation in the fundamental frequency contour of the singing voice. They can be used for search and retrieval of music and for expressive singing voice synthesis based on singing style since they strongly reflect the individuality of the singer. The fundamental frequency contour of the singing voice is estimated using the Viterbi algorithm with limitation from a corresponding note sequence. Next, the notes are aligned with the fundamental frequency sequence temporally. Finally, each expression is identified and parameterized in accordance with designed rules. Experiments demonstrated that this method can transcribe expressions in the singing voice from commercial recordings.