Stride-k Subsampling: Train-Free Audio Token Reduction for Whisper

Chanhee Cho, Junhyuk Choi, Bugeun Kim


Abstract
Whisper exposes speech through a fixed 1500-token encoder interface, now a default representation for ASR decoders and Whisper-based speech language models (SpeechLMs), yet its redundancy remains largely unexamined. We propose stride-k subsampling, a deterministic indexing operation that retains every k-th token after the convolutional stem or encoder transformer. Across five Whisper scales, k=2 preserves baseline WER at both positions, with CKA attributing this stability to acoustic overlap at the stem and attention-induced redistribution at the encoder output. Applying stride-2 at both positions cuts audio tokens by 75% and total GFLOPs by 52–58%, with small WER costs on most ASR benchmarks and larger costs on harder ones. The same configuration extends to three Whisper-based SpeechLMs, yielding modest accuracy drops on stronger baselines and larger drops on weaker ones, while reducing end-to-end latency by 19.6–27.4%. Requiring no training or auxiliary computation, stride-k subsampling suggests that the standard Whisper audio-token interface is over-provisioned for many downstream uses.
Anthology ID:
2026.emnlp-main.1608
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
36572–36599
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1608/
DOI:
Bibkey:
Cite (ACL):
Chanhee Cho, Junhyuk Choi, and Bugeun Kim. 2026. Stride-k Subsampling: Train-Free Audio Token Reduction for Whisper. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 36572–36599, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Stride-k Subsampling: Train-Free Audio Token Reduction for Whisper (Cho et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1608.pdf