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arXiv · 2608.05727

LILAC: An Idempotent Neural Speech Codec

June Young Yi·Dongwook Lee·Jiheum Yeom·Sungroh Yoon
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Abstract

Neural Audio Codecs are widely adopted in speech generation and editing. However, existing neural audio codecs are not idempotent: across the paper's twelve baseline systems, every configuration tested rewrites, on average, at least 15% of its tokens in a single decode-re-encode pass. This poses a problem for utilizing Neural Audio Codecs as token interfaces in pipelines where re-encoding decoded outputs can occur. We present LILAC, a fully convolutional 24 kHz speech codec at 9.375 Hz and 0.75 kbit/s that is codec idempotent by construction; re-encoding the decoded audio of any valid token stream returns the identical stream. LILAC achieves idempotency while maintaining competitive quality, reaching UTMOS 4.14 and 4.24 on LibriSpeech and LibriTTS-R test sets, comparable to SOTA sub-1 kbit/s Neural Audio Codecs.

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June Young Yi, Dongwook Lee, Jiheum Yeom, Sungroh Yoon. 2026-08-06. LILAC: An Idempotent Neural Speech Codec. https://arxiv.org/abs/2608.05727

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