A Law

[dvisockas]

🚀 Feature

I would like to propose adding of A-Law to torchaudio.transforms

Motivation

A-law is a companding algorithm similar to mu-law (that is already in torchaudio). It is used in European 8-bit PCM systems. By convention, A-law is used for an international connection if at least one country uses it. With these transforms torchaudio would
enable even wider modelling capabilities of telephony audio.

Pitch

I imagine the API could be almost identical to MuLaw with one caveat - the compression parameter A would be an additional parameter. So at the end there would be two additional transforms ALawEncoding and ALawDecoding.

Additional context

I have already written the code and would be happy to open a PR.

[vincentqb]

Yes, this would be a good addition :)

To verify correctness, do you have a reference implementation to test and compare against? I'm adding a few pointers to make sure we cover all that needs to be covered here for a new transform to be added. If you have any questions about them before opening a pull request, please feel free to ask clarification :) Does that help?

[dvisockas]

Haven't found a reference implementation, but will look for it :)

[dvisockas]

Does the TODO in PR #930 look good?

[dvisockas]

The only reference implementation I seem to find is the wikipedia graph:

Running a linspace vector through unquantized A law encoding yields:

[vincentqb]

Does the TODO in PR #930 look good?

I've updated the comment to make it clearer what's entailed :)