Dithering constant

Why do torchaudio.compliance.kaldi.fbank and torchaudio.compliance.kaldi.spectrogram have so large dither default parameter (=1.0)? It very often just noises full output.

It’s common to use dither around 0, e.g 0.00001 in QuartzNet, Jasper – near to SOTA ASR models (https://github.com/NVIDIA/NeMo/blob/master/examples/asr/configs/quartznet15x5.yaml).

I want to notice that even in torchaudio tutorial we have dither = 0.0: https://pytorch.org/tutorials/beginner/audio_preprocessing_tutorial.html.

Also look at this issue and how it was resolved: https://github.com/pytorch/audio/issues/157

[csukuangfj]

Why do torchaudio.compliance.kaldi.fbank and torchaudio.compliance.kaldi.spectrogram have so large dither default parameter (=1.0)

Kaldi uses 1 as the default dither value. It is fine for Kaldi because waveform in kaldi has a range [-32768, 32767]. 1 is relatively small compared to the maximum value 32767.

However, in torchaudio,

torchaudio.load(filename)

returns a tensor with values in the range [-1, 1]. So if you still use the default value 1 from Kaldi, you will distort the audio signal.

[popcornell]

Second this, the default right now makes the whole torchaudio.compliace.kaldi features totally unusable out-of-the-box. I spent one hour looking at possible bugs on labels only to find out that basically my model was fed noise because of the dither default value.