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Sparse autoencoders found 684 interpretable features inside a voice-cloning TTS model, and probing strength did not predict steering strength

AspireAI community · arXiv
Voice-cloning TTS models synthesize an unseen speaker from a brief prompt, but which acoustic properties they represent and use was unclear. This paper applies a feature-based interpretability framework, using sparse autoencoders, PCA and random directions through sparse probing, steering and quantitative auto-interpretability, focusing on Qwen3-TTS and extending probing and steering to five more models to test generalization across architectures. The models encode concepts like pitch, energy, noise and accent, but the central finding is that sparse prediction and steering are effective only for some concepts, that strong probing does not always translate to steering or the reverse, that sparse autoencoders are useful for probing known concepts and discovering new ones while PCA stays competitive for dense probing and steering, and that auto-interpretability surfaced 684 automatically validated sparse autoencoder features in Qwen3-TTS covering speaker clusters, speaking style and recording conditions beyond known concepts. The paper is under review.
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