audiofilters: Add Distortion effect

[relic-se]

New audio effects class, audiofilters.Distortion, to distort audio samples using one of the available modes available in the audiofilters.DistortionMode enum.

Todo:

• Reduce floating point computation overhead for DistortionMode.CLIP, DistortionMode.OVERDRIVE and DistortionMode.WAVESHAPE algorithms.
• Test with unsigned and 8 bit sources.

Comments:

• Should tone-shaping of some form be included within this class or require the use of an audiofilters.Filter effect? (ie: filter.play(distortion.play(sample)))
• Any addition mode suggestions would be appreciated. The size overhead of including additional algorithms is very minimal. I'd only want to avoid redundant or unnecessary modes which may cause confusion (hence why I didn't include the ATAN mode within the Godot Engine).
• The pre_gain and post_gain properties are currently measured in decibels which requires the addition of a db_to_linear function to make those values linear. Would it be more ideal to forego decibels altogether and make those properties linear?

Parameters, documentation copy and algorithms are mostly credited to Godot Engine under the MIT License.

• Documentation: https://docs.godotengine.org/en/stable/classes/class_audioeffectdistortion.html.
• Code: https://github.com/godotengine/godot/blob/master/servers/audio/effects/audio_effect_distortion.cpp

Example Code:

import board
import audiobusio
import audiofilters
import audiocore
import digitalio
import adafruit_debouncer

audio = audiobusio.I2SOut(bit_clock=board.GP0, word_select=board.GP1, data=board.GP2)

wave_file = open("StreetChicken.wav", "rb")
wave = audiocore.WaveFile(wave_file)

effect = audiofilters.Distortion(
    buffer_size=1024,
    channel_count=wave.channel_count,
    sample_rate=wave.sample_rate,
    mix=0.0,
    pre_gain=0.0,
    post_gain=-10.0,
    drive=0.5,
)
effect.play(wave, loop=True)
audio.play(effect)

button_mix_pin = digitalio.DigitalInOut(board.GP3)
button_mix_pin.direction = digitalio.Direction.INPUT
button_mix = adafruit_debouncer.Debouncer(button_mix_pin)

button_mode_pin = digitalio.DigitalInOut(board.GP4)
button_mode_pin.direction = digitalio.Direction.INPUT
button_mode = adafruit_debouncer.Debouncer(button_mode_pin)

modes = [
#    (Mode, pre_gain, drive, post_gain),
    (audiofilters.DistortionMode.CLIP, 0.0, 0.5, -10.0),
    (audiofilters.DistortionMode.LOFI, 0.0, 0.9, -2.0),
    (audiofilters.DistortionMode.OVERDRIVE, 20.0, 0.5, -15.0),
    (audiofilters.DistortionMode.WAVESHAPE, 10.0, 0.75, -20.0),
]
mode_index = 0

# Initial state
print("off")
print(effect.mode)

while True:
    button_mix.update()
    if button_mix.rose:
        effect.mix = not effect.mix
        print("on" if effect.mix else "off")
    
    button_mode.update()
    if button_mode.rose:
        mode_index = (mode_index + 1) % len(modes)
        effect.mode, effect.pre_gain, effect.drive, effect.post_gain = modes[mode_index]
        print(effect.mode)

[RAWJUNGLE]

I think we need to add more fluff for the full effects package as well.

• Maybe a bitcrasher?

[relic-se]

I think we need to add more fluff for the full effects package as well.

* Maybe a bitcrasher?

I don't know exactly what you mean by "fluff", but the audiofilters.DistortionMode.LOFI is a bitcrusher. In fact, it may need to be renamed to better represent that.