🐛 Bug

If you use STFT through Spectrogram, with power=1, you can easily get a NaN. If your spectrogram square magnitude underflows to zero, you end up taking backprop of sqrt(0), which leads to a NaN.

To Reproduce

Steps to reproduce the behavior:

1. Use torchaudio.transforms.Spectrogram, set power=1, do a backward pass.

Expected behavior

There should be a configurable epsilon to clamp the input to sqrt, otherwise users have to use torch.stft directly or use other workarounds (such as power=2).