Add Inverse Short Time Fourier Transform in ATen native

[mthrok]

Ported torchaudio's implementation (test, and documentation as well) to ATen.

Note

• Batch packing/unpacking is performed in Python. ATen implementation expects 4D input tensor.
• The way hop_length is initialized in the same way as stft implementation. The Torchaudio's version tried to mimic the same behavior but slightly different.

Closes #34827
Relates #3775

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This comment has been revised 101 times.

[mthrok]

FYI: There is a ongoing discussion on ways to extend istft for custom padding pytorch/audio#500 pytorch/audio#427 .

[vincentqb]

Overall, LGTM :) see comments below

• Batch packing/unpacking is performed in Python. ATen implementation expects 4D input tensor.

I'm assuming you did so to mirror the stft implementation? This means that the libtorch implementation will behave differently from the python implementation, right?

• The way hop_length is initialized in the same way as stft implementation. The Torchaudio's version tried to mimic the same behavior but slightly different.

The initialization in ATen seems fine to me. Can you clarify if it changes something for the user in python?

[vincentqb]

FYI: There is a ongoing discussion on ways to extend istft for custom padding pytorch/audio#500 pytorch/audio#427 .

Let's leave these changes for a follow-up PR.

[vincentqb]

All the tests are green!

LGTM :)

[vincentqb]

@mthrok -- can you import the PR so that the internal tests run too?

[facebook-github-bot]

@mthrok has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@mthrok merged this pull request in 5a27ec0.