Introduce `functional` submodule (#1003)

torchaudio/functional/__init__.py

+from .functional import (
+    allpass_biquad,
+    amplitude_to_DB,
+    angle,
+    band_biquad,
+    bandpass_biquad,
+    bandreject_biquad,
+    bass_biquad,
+    biquad,
+    DB_to_amplitude,
+    complex_norm,
+    compute_deltas,
+    contrast,
+    create_dct,
+    create_fb_matrix,
+    dither,
+    dcshift,
+    deemph_biquad,
+    detect_pitch_frequency,
+    equalizer_biquad,
+    flanger,
+    gain,
+    griffinlim,
+    highpass_biquad,
+    lfilter,
+    lowpass_biquad,
+    magphase,
+    mask_along_axis,
+    mask_along_axis_iid,
+    mu_law_encoding,
+    mu_law_decoding,
+    overdrive,
+    phase_vocoder,
+    phaser,
+    riaa_biquad,
+    sliding_window_cmn,
+    spectrogram,
+    treble_biquad,
+    vad,
+)

torchaudio/functional.py → torchaudio/functional/functional.py

@@ -12,6 +12,8 @@ __all__ = [
     "spectrogram",
     "griffinlim",
     "amplitude_to_DB",
+    "DB_to_amplitude",
+    "compute_deltas",
     "create_fb_matrix",
     "create_dct",
     "mu_law_encoding",
@@ -19,6 +21,8 @@ __all__ = [
     "complex_norm",
     "angle",
     "magphase",
+    "dither",
+    "gain",
     "phase_vocoder",
     "lfilter",
     "lowpass_biquad",
@@ -38,6 +42,7 @@ __all__ = [
     "overdrive",
     "phaser",
     "flanger",
+    "detect_pitch_frequency",
     'mask_along_axis',
     'mask_along_axis_iid',
     'sliding_window_cmn',