Add functionals gain, dither, scale_to_interval

[CamiWilliams]

Added functionality for SoX capabilities.

See comment in issue #260 for details.

Gain : Apply amplification or attenuation to the audio signal.

def gain(waveform, gain_db=1.0):
    # type: (Tensor, float) -> Tensor

Scale to Interval : Scales waveform to an interval.

def scale_to_interval(waveform, interval=1.0):
    # type: (Tensor, float) -> Tensor

Dither: Maximize the dynamic range of audio stored at a particular bit-depth.

def dither(waveform, probability_density_function="TPDF", noise_shaping=False, ns_filter=""):
    # type: (Tensor, str, bool, str) -> Tensor

Updated VCTK dataset code to replace SoX

E.append_effect_to_chain("gain", ["-h"])
E.append_effect_to_chain("channels", [1])
E.append_effect_to_chain("rate", [16000])
E.append_effect_to_chain("gain", ["-rh"])
E.append_effect_to_chain("dither", ["-s"])

is equivalent to

wf_vctk, sr_vctk = torchaudio.load(test_filepath_vctk)
sample = T.Resample(sr_vctk, 16000, resampling_method='sinc_interpolation')
wf_vctk = sample(wf_vctk)
wf_vctk = F.dither(wf_vctk, noise_shaping=True)

[vincentqb]

See comment in #260 for VCTK.

[vincentqb]

This should just be an internal function, and it in fact does the core of applying dither. Let's rename this to _apply_dither.

nit: "Apply dither to the waveform using the chosen density function."

[vincentqb]

I see this comment marked as resolved. What was the resolution of this?

[CamiWilliams]

Just pushed the change, I renamed it to _apply_probability_distribution. How does that sound?

[CamiWilliams]

per this comment

[CamiWilliams]

And this comment... should I still rename to "apply dither"?

[vincentqb]

It's almost good to go. As mentioned in the comments:

• Let's use a file different from a sine wave for testing, see other assets.
• Let's remove scale_to_interval from this PR.
• Let's make probability_distribution private with a different name like _apply_dither.

[vincentqb]

I see this comment marked as resolved. What was the resolution of this?

[vincentqb]

LGTM! Good job, I'm merging!