[Audio] Remove torchaudio from spectrogram transforms

[anteju]

What does this PR do ?

This PR removes use of torchaudio from AudioToSpectrogram and SpectrogramToAudio.
Classes using torchaudio are kept under AudioToSpectrogamTA and SpectrogramToAudioTA, similarly to FilterbankFeatures and FilterbankFeaturesTA.

Collection: audio

Changelog

• Removed torchaudio requirement for AudioToSpectrogram and SpectrogramToAudio
• Added unit tests to check analysis, synthesis, and reconstruction
• Added unit tests to check the update is matching torchaudio version

Usage

• You can potentially add a usage example below

# Prepare analysis and synthesis transforms
encoder = AudioToSpectrogram(fft_length=fft_length, hop_length=hop_length)
decoder = SpectrogramToAudio(fft_length=fft_length, hop_length=hop_length)

# Analysis transform, input shape (B, C, T)
X, _ = encoder(input=x)

# Synthesis transform, output shape (B, C, T)
y, _ = decoder(input=Y)

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Additional Information

• Related to # (issue)

[racoiaws]

Overall LGTM, but needs documenting of all reshapes (e.g. via einops)

[racoiaws]

LGTM