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Self-Taught Recognizer: Toward Unsupervised Adaptation for Speech Foundation Models
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Proposes STAR, a source-free unsupervised adaptation method for speech foundation models that uses a token-level STAR indicator (combining confidence and attentive scores) to re-weight pseudo-label finetuning, plus utterance-level filtering.
Problem
Adapting attention-based speech foundation models (e.g., Whisper) to noisy, accented, and specific target domains without ground-truth labels or source data, where pseudo-label quality is hard to assess because softmax confidence is unreliable.
Approach
A novel token-level quality indicator that integrates decoder self-attention aggregate scores (reliable but unstable) with softmax confidence (stable but unreliable) through conflict/consistency-aware sigmoid gating, used to re-weight the ASR cross-entropy loss during self-training; combined with utterance-level filtering via Gaussian weight perturbation.
Key results
- STAR reduces WER by an average of 13.5% relative across 14 target domains with Whisper-Large-V3, e.g., -24.9% on LS-FreeSound babble and -20.0% on CommonVoice African.
- STAR approaches the supervised upper bound on some domains, e.g., CHiME-4 dev-real 3.9 vs 3.2 real-label WER and LS-FreeSound car 2.5 vs 2.4.
- STAR achieves over 10% relative WER reduction on OWSM, Canary, Parakeet-TDT, and yields up to 30.7% reduction with SeamlessM4T-V2 on CHiME-4 dev-real; ST gains average over 1.2 BLEU on FLEURS X-to-En.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| use STAR adaptation instead of attentive-score token reweighting | Whisper-Large-V3 · 14 ASR target domains | WER (%): 6.2 -> 6.0; 9.5 -> 9.4; 4.1 -> 3.9; 6.6 -> 6.4; 31.3 -> 30.2; 15.0 -> 14.8; 2.6 -> 2.5; 44.9 -> 44.6; 5.0 -> 4.8; 5.2 -> | Helped |
| add utterance-level filtering to STAR (ablation) | STAR with Whisper-Large-V3 · CHiME-4 test-real | WER (%): 6.2 -> 6.0 | Helped |
| replace Gaussian disturbance filtering with beam search decoding (ablation) | utterance-level filtering · CHiME-4 test-real | WER (%): 6.4 -> 6.6 | Hurt |
| replace Gaussian disturbance filtering with consensus decoding (ablation) | utterance-level filtering · CHiME-4 test-real | WER (%): 6.4 -> 6.6 | Hurt |
| replace confidence token scores with attentive scores (ablation) | token-level reweighting · ASR target domains | WER (%) | Helped |
| use confidence-only token reweighting rather than STAR (ablation) | Whisper-Large-V3 · ASR target domains | WER (%) | Hurt |
| use attentive-score-only token reweighting rather than STAR (ablation) | Whisper-Large-V3 · ASR target domains | WER (%) | Hurt |
| freeze part of the model parameters during STAR finetuning (ablation) | STAR · CHiME-4 test-real | WER (%) | Hurt |
| use LoRA tuning instead of full finetuning (ablation) | STAR · CHiME-4 test-real | WER (%) | No clear effect |
| repeat pseudo-labeling and STAR adaptation for multiple iterations (ablation) | STAR · CHiME-4 test-real, Whisper large-v3 | WER (%): 6.0 -> 5.7 | Helped |
Surprising findings
- Adapting to CHiME-4 with STAR improves performance on other unrelated domains rather than causing catastrophic forgetting, without recalling source data.
- Softmax confidence is unreliable for Whisper: 52% of correct tokens get low confidence and 60% of wrong tokens get high confidence.
Limitations
- Relies on large, universally robust speech foundation models as pseudo-labelers; smaller domain-specific models (WavLM-Conformer, RNN-T) are not suitable.
- Gains are limited on colloquial and challenging data (SwitchBoard, CORAAL, RATS), where pseudo labels are poor and improvements mainly reflect function-word adjustments.
- Requires multiple decoding passes with weight perturbation for utterance-level filtering, adding compute; several hyperparameters (lambda, tau, alpha) are set empirically.
Experimental setup
Datasets: CHiME-4 LibriSpeech-FreeSound RATS CommonVoice 5.1 TED-LIUM 3 SwitchBoard LRS2 ATIS CORAAL FLEURS
Benchmarks: CHiME-4 LibriSpeech-FreeSound RATS CommonVoice TED-LIUM 3 SwitchBoard LRS2 ATIS CORAAL FLEURS X-to-En
Metrics: word error rate BLEU normalized cross-entropy
Baselines: Whisper (frozen) Whisper (self-train.) Whisper (real label) UTT_filter TOK_reweight (confidence) TOK_reweight (attentive) beam search filtering consensus decoding filtering
Builds on: Whisper self-training focal loss Monte Carlo dropout consensus decoding
Closest papers by meaning
- Master-ASR: Achieving Multilingual Scalability and Low-Resource Adaptation in ASR with Modular Learning (ICML 2023 · similarity 0.89)
- Unified Speech Recognition: A Single Model for Auditory, Visual, and Audiovisual Inputs (NeurIPS 2024 · similarity 0.89)
- In-Situ Text-Only Adaptation of Speech Models with Low-Overhead Speech Imputations (ICLR 2023 · similarity 0.89)
- Speech Recognition Meets Large Language Model: Benchmarking, Models, and Exploration (AAAI 2025 · similarity 0.88)
- UniWav: Towards Unified Pre-training for Speech Representation Learning and Generation (ICLR 2025 · similarity 0.86)
- E-BATS: Efficient Backpropagation-Free Test-Time Adaptation for Speech Foundation Models (NeurIPS 2025 · similarity 0.85)
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