A.3 Data transformation

The Mel spectrogram is normalized with the global mean (-5.8843) and standard deviation (2.2615) to
stabilize training. The statistics are estimated on 30k random training samples from the 1K hours of

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English audio. Input and output duration are dequantized (x ∼ U[x − 0.5, x + 0.5]) and transformed
with log(1 + x) following [Ren et al., 2021]. Prediction of duration is quantized and clipped such
that the minimal duration is greater than or equal to zero.

A.4 Cross-lingual zero-shot TTS test data filtering
Voicebox-Text-GuidedMultilingual UniversalSpeechGenerationatScale