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arXiv · 2509.16195

FocalCodec-Stream: Streaming Low-Bitrate Speech Coding via Causal Distillation

Luca Della Libera·Cem Subakan·Mirco Ravanelli
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Abstract

Neural audio codecs are a fundamental component of modern generative audio pipelines. Although recent codecs achieve strong low-bitrate reconstruction and provide powerful representations for downstream tasks, most are non-streamable, limiting their use in real-time applications. We present FocalCodec-Stream, a hybrid codec based on focal modulation that compresses speech into a single binary codebook at 0.55 - 0.80 kbps with a theoretical latency of 80 ms. Our approach combines multi-stage causal distillation of WavLM with targeted architectural improvements, including a lightweight refiner module that enhances quality under latency constraints. Experiments show that FocalCodec-Stream outperforms existing streamable codecs at comparable bitrates, while preserving both semantic and acoustic information. The result is a favorable trade-off between reconstruction quality, downstream task performance, latency, and efficiency. Code and checkpoints will be released at https://github.com/lucadellalib/focalcodec.

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Luca Della Libera, Cem Subakan, Mirco Ravanelli. 2025-09-19. FocalCodec-Stream: Streaming Low-Bitrate Speech Coding via Causal Distillation. https://arxiv.org/abs/2509.16195

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