Include synthio.Biquad methods within audiofilters.Filter

[relic-se]

This is a minor modification to the previously merged PR #9744.

This modification adds the following methods to the audiofilters.Filter class:

• audiofilters.Filter.low_pass_filter
• audiofilters.Filter.high_pass_filter
• audiofilters.Filter.bass_pass_filter

These new methods help facilitate the generation of synthio.Biquad objects for the filter effect without requiring an instance of synthio.Synthesizer. It also ensures that the sample rate used for the filter calculations matches the effect.

Here is a modified version of the example provided in #9744 with this change in place:

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

Q = 2.0

audio = audiobusio.I2SOut(bit_clock=board.GP2, word_select=board.GP3, data=board.GP4)

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

effect = audiofilters.Filter(buffer_size=1024, channel_count=wave.channel_count, sample_rate=wave.sample_rate, mix=1.0)
effect.play(wave, loop=True)
audio.play(effect)

button_up_pin = digitalio.DigitalInOut(board.GP0)
button_up_pin.direction = digitalio.Direction.INPUT
button_up = adafruit_debouncer.Debouncer(button_up_pin)

button_down_pin = digitalio.DigitalInOut(board.GP1)
button_down_pin.direction = digitalio.Direction.INPUT
button_down = adafruit_debouncer.Debouncer(button_down_pin)

position = 1.0
def update_filter():
    frequency = (min(max(position, 0.0), 1.0) ** 2) * (wave.sample_rate / 2 - 25) + 25
    print("{}hz".format(frequency))
    effect.low_pass_filter(frequency, Q)
update_filter()

while True:
    button_up.update()
    if button_up.rose:
        position = min(position + 0.025, 1.0)
        update_filter()
        
    button_down.update()
    if button_down.rose:
        position = max(position - 0.025, 0.0)
        update_filter()

The only consideration I have is whether or not to automatically update the filter internally or return the synthio.Biquad object to set manually. This is how that implementation would look like:

effect.filter = effect.low_pass_filter(frequency, Q)

[relic-se]

I've changed this PR to a draft, because I am currently contemplating the possibility of implementing multiple synthio.Biquad objects on a single audiofilters.Filter effect. Doing so would require that the synthio.Biquad objects generated by the newly added methods (ie: audiofilters.Filter.low_pass_filter) would not automatically update the audiofilters.Filter.filter property.

[relic-se]

I've decided to have the new methods simply return the synthio.Biquad object rather than update the filter property, because that will work better for future updates to this class (support for multiple biquads).

I've also added a deprecation notice in correspondence with #9756. However, this does cause an error in the docs because that PR hasn't been merged yet and synthio.BlockBiquad doesn't exist in this branch.

I don't plan on doing any more work on this PR. This addition may be entirely unnecessary at this point, so it is alright by me to reject the PR.