You are provided with the abstract of a scientific paper and the abstracts of the papers it references. Your task is to write a Related Work section for the main paper. This section should concisely summarize and integrate the key points from the cited abstracts, reflecting how they relate to the main paper's contributions and context. In your summary, use numerical citation markers like [1], [2], etc., to refer to the corresponding papers.

Main Abstract:
We present a deep learning method for singing voice conversion. The proposed network is not conditioned on the text or on the notes, and it directly converts the audio of one singer to the voice of another. Training is performed without any form of supervision: no lyrics or any kind of phonetic features, no notes, and no matching samples between singers. The proposed network employs a single CNN encoder for all singers, a single WaveNet decoder, and a classifier that enforces the latent representation to be singer-agnostic. Each singer is represented by one embedding vector, which the decoder is conditioned on. In order to deal with relatively small datasets, we propose a new data augmentation scheme, as well as new training losses and protocols that are based on backtranslation. Our evaluation presents evidence that the conversion produces natural signing voices that are highly recognizable as the target singer.

Cited Abstract(s):
[1]: This paper presents techniques to improve the quality of voices generated through statistical singing voice conversion with direct waveform modification based on spectrum differential (DIFFSVC). The DIFFSVC method makes it possible to convert singing voice characteristics of a source singer into those of a target singer without using vocoder-based waveform generation. However, quality of the converted singing voice still degrades compared to that of a natural singing voice due to various factors, such as the over-smoothing of the converted spectral parameter trajectory. To alleviate this over-smoothing, we propose a technique to restore the global variance of the converted spectral parameter trajectory within the framework of the DIFFSVC method. We also propose another technique to specifically avoid over-smoothing at unvoiced frames. Results of subjective and objective evaluations demonstrate that the proposed techniques significantly improve speech quality of the converted singing voice while preserving the conversion accuracy of singer identity compared to the conventional DIFFSVC.

[2]: This paper presents a novel statistical singing voice conversion (SVC) technique with direct waveform modification based on the spectrum differential that can convert voice timbre of a source singer into that of a target singer without using a vocoder to generate converted singing voice waveforms. SVC makes it possible to convert singing voice characteristics of an arbitrary source singer into those of an arbitrary target singer. However, speech quality of the converted singing voice is significantly degraded compared to that of a natural singing voice due to various factors, such as analysis and modeling errors in the vocoderbased framework. To alleviate this degradation, we propose a statistical conversion process that directly modifies the signal in the waveform domain by estimating the difference in the spectra of the source and target singers’ singing voices. The differential spectral feature is directly estimated using a differential Gaussian mixture model (GMM) that is analytically derived from the traditional GMM used as a conversion model in the conventional SVC. The experimental results demonstrate that the proposed method makes it possible to significantly improve speech quality in the converted singing voice while preserving the conversion accuracy of singer identity compared to the conventional SVC. Index Terms: singing voice, statistical voice conversion, vocoder, Gaussian mixture model, differential spectral compensation

[3]: This work address the application of Voice Conversion to singing-voice. The GMM-based approach was applied to VOCALOID, a concatenative singing synthesizer, to perform singer timbre conversion. The conversion framework was applied to full-quality singing databases, achieving a satisfactory conversion effect on the synthesized utterances. We report in this paper the results of our experimentation focused to study the spectral conversion performance when applied to specific pitch-range data.
In the field of singing voice conversion, i.e., transforming an audio of a song to a target voice, almost all literature methods have used parallel data [1] [2] [3] , i.e., different singers that are required to perform the same song. None of these existing methods provide code or benchmarks that can be used for a direct comparison of their results (even if supervised) to ours.