[Audio] Metric with Squim objective and MOS

[anteju]

What does this PR do ?

Add a Metric object for calculating Squim MOS.

Collection: audio

Changelog

• Added a metric wrapper for Squim objective and MOS models
• Added unit tests
• Fixed a bug in transcribe_utils

Usage

For example, in model config:

...
model:
...
  metrics:
    val:
      squim_mos: # Squim MOS
        _target_: nemo.collections.audio.metrics.SquimMOSMetric
        fs: ${model.sample_rate}
      squim_stoi: # Squim STOI
        _target_: nemo.collections.audio.metrics.SquimObjectiveMetric
        metric: stoi
        fs: ${model.sample_rate}
...

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Additional Information

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[racoiaws]

LGTM