Producing real looking audio requires modeling data represented at completely different scales. For instance, simply as music builds complicated musical phrases from particular person notes, speech combines temporally native buildings, resembling phonemes or syllables, into phrases and sentences. Creating well-structured and coherent audio sequences in any respect these scales is a problem that has been addressed by coupling audio with transcriptions that may information the generative course of, be it textual content transcripts for speech synthesis or MIDI representations for piano. Nevertheless, this strategy breaks when making an attempt to mannequin untranscribed features of audio, resembling speaker traits essential to assist folks with speech impairments get better their voice, or stylistic parts of a piano efficiency.
In “AudioLM: a Language Modeling Strategy to Audio Technology”, we suggest a brand new framework for audio technology that learns to generate real looking speech and piano music by listening to audio solely. Audio generated by AudioLM demonstrates long-term consistency (e.g., syntax in speech, melody in music) and excessive constancy, outperforming earlier programs and pushing the frontiers of audio technology with purposes in speech synthesis or computer-assisted music. Following our AI Ideas, we have additionally developed a mannequin to establish artificial audio generated by AudioLM.
From Textual content to Audio Language Fashions
In recent times, language fashions skilled on very giant textual content corpora have demonstrated their distinctive generative skills, from open-ended dialogue to machine translation and even common sense reasoning. They’ve additional proven their capability to mannequin different indicators than texts, such as pure photos. The important thing instinct behind AudioLM is to leverage such advances in language modeling to generate audio with out being skilled on annotated knowledge.
Nevertheless, some challenges must be addressed when transferring from textual content language fashions to audio language fashions. First, one should deal with the truth that the information fee for audio is considerably greater, thus resulting in for much longer sequences — whereas a written sentence will be represented by just a few dozen characters, its audio waveform sometimes incorporates lots of of 1000’s of values. Second, there’s a one-to-many relationship between textual content and audio. Which means the identical sentence will be rendered by completely different audio system with completely different talking types, emotional content material and recording situations.
To beat each challenges, AudioLM leverages two sorts of audio tokens. First, semantic tokens are extracted from w2v-BERT, a self-supervised audio mannequin. These tokens seize each native dependencies (e.g., phonetics in speech, native melody in piano music) and world long-term construction (e.g., language syntax and semantic content material in speech, concord and rhythm in piano music), whereas closely downsampling the audio sign to permit for modeling lengthy sequences.
Nevertheless, audio reconstructed from these tokens demonstrates poor constancy. To beat this limitation, along with semantic tokens, we depend on acoustic tokens produced by a SoundStream neural codec, which seize the small print of the audio waveform (resembling speaker traits or recording situations) and permit for high-quality synthesis. Coaching a system to generate each semantic and acoustic tokens leads concurrently to excessive audio high quality and long-term consistency.
Coaching an Audio-Solely Language Mannequin
AudioLM is a pure audio mannequin that’s skilled with none textual content or symbolic illustration of music. AudioLM fashions an audio sequence hierarchically, from semantic tokens as much as positive acoustic tokens, by chaining a number of Transformer fashions, one for every stage. Every stage is skilled for the subsequent token prediction primarily based on previous tokens, as one would practice a textual content language mannequin. The primary stage performs this process on semantic tokens to mannequin the high-level construction of the audio sequence.
Within the second stage, we concatenate the whole semantic token sequence, together with the previous coarse acoustic tokens, and feed each as conditioning to the coarse acoustic mannequin, which then predicts the longer term tokens. This step fashions acoustic properties resembling speaker traits in speech or timbre in music.
Within the third stage, we course of the coarse acoustic tokens with the positive acoustic mannequin, which provides much more element to the ultimate audio. Lastly, we feed acoustic tokens to the SoundStream decoder to reconstruct a waveform.
After coaching, one can situation AudioLM on just a few seconds of audio, which allows it to generate constant continuation. To be able to showcase the final applicability of the AudioLM framework, we contemplate two duties from completely different audio domains:
- Speech continuation, the place the mannequin is predicted to retain the speaker traits, prosody and recording situations of the immediate whereas producing new content material that’s syntactically right and semantically constant.
- Piano continuation, the place the mannequin is predicted to generate piano music that’s coherent with the immediate when it comes to melody, concord and rhythm.
Within the video under, you possibly can take heed to examples the place the mannequin is requested to proceed both speech or music and generate new content material that was not seen throughout coaching. As you hear, word that every little thing you hear after the grey vertical line was generated by AudioLM and that the mannequin has by no means seen any textual content or musical transcription, however fairly simply discovered from uncooked audio. We launch extra samples on this webpage.
To validate our outcomes, we requested human raters to take heed to brief audio clips and resolve whether or not it’s an authentic recording of human speech or an artificial continuation generated by AudioLM. Based mostly on the scores collected, we noticed a 51.2% success fee, which isn’t statistically considerably completely different from the 50% success fee achieved when assigning labels at random. Which means speech generated by AudioLM is tough to tell apart from actual speech for the common listener.
Our work on AudioLM is for analysis functions and we have now no plans to launch it extra broadly right now. In alignment with our AI Ideas, we sought to grasp and mitigate the chance that individuals may misread the brief speech samples synthesized by AudioLM as actual speech. For this function, we skilled a classifier that may detect artificial speech generated by AudioLM with very excessive accuracy (98.6%). This reveals that regardless of being (nearly) indistinguishable to some listeners, continuations generated by AudioLM are very straightforward to detect with a easy audio classifier. It is a essential first step to assist defend towards the potential misuse of AudioLM, with future efforts doubtlessly exploring applied sciences resembling audio “watermarking”.
Conclusion
We introduce AudioLM, a language modeling strategy to audio technology that gives each long-term coherence and excessive audio high quality. Experiments on speech technology present not solely that AudioLM can generate syntactically and semantically coherent speech with none textual content, but in addition that continuations produced by the mannequin are nearly indistinguishable from actual speech by people. Furthermore, AudioLM goes effectively past speech and might mannequin arbitrary audio indicators resembling piano music. This encourages the longer term extensions to different sorts of audio (e.g., multilingual speech, polyphonic music, and audio occasions) in addition to integrating AudioLM into an encoder-decoder framework for conditioned duties resembling text-to-speech or speech-to-speech translation.
Acknowledgments
The work described right here was authored by Zalán Borsos, Raphaël Marinier, Damien Vincent, Eugene Kharitonov, Olivier Pietquin, Matt Sharifi, Olivier Teboul, David Grangier, Marco Tagliasacchi and Neil Zeghidour. We’re grateful for all discussions and suggestions on this work that we acquired from our colleagues at Google.
