The ASR systems used to grade text-to-speech miss 33-67% of very rare words even when a human says them correctly
AspireAI community · arXiv (cs.SD) — BitmanagerAI / lab260
Text-to-speech is normally evaluated by transcribing the output with an automatic speech recognizer and computing word error rate, which quietly measures two systems at once — if the recognizer cannot hear a word, an error there says little about the TTS engine. This paper measures that floor by running the same recognizers on the original human recordings of the test sentences. On LibriSpeech and FLEURS the evaluation recognizer misses 33% to 67% of very rare words even in human speech, and all three recognizers miss 22% to 42%. Adjudicating every word with two more recognizer families cuts apparent TTS error on rare LibriSpeech words from 10-13% to 3-5%, and the paper shows that simply masking out words the recognizer misses in human speech is itself biased: other recognizers find real TTS errors on those words far more often (4-6% versus 0.2-0.3%) and overturn about half of the errors that mask keeps. The authors note that as many as half the remaining adjudicated errors may be spelling variants, so a listening test is still needed.
Read the story and explore more from the AspireAI community.
Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.