Add new audiospeed.Resampler module

[relic-se]

Automatically resamples source sample to match destination sample rate. Shares fixed point speed functionality with audiospeed.SpeedChanger.

Demonstration using pico_test_synth with raspberry_pi_pico:

import array
import audiobusio
import audiocore
import audiomixer
import audiospeed
import board
import math
import time

IN_SAMPLE_RATE = 32000
OUT_SAMPLE_RATES = (8000, 11025, 16000, 22050, 32000, 44100, 48000, 88200, 96000)

# Set up audio output
audio = audiobusio.I2SOut(bit_clock=board.GP20, word_select=board.GP21, data=board.GP22)

# Generate one period of sine wave
length = IN_SAMPLE_RATE // 440
sine_wave = array.array("H", [0] * length)
for i in range(length):
    sine_wave[i] = min(max(int(math.sin(math.pi * 2 * i / length) * (2 ** 15) + 2 ** 15), -65536), 65535)
sine_wave = audiocore.RawSample(sine_wave, sample_rate=IN_SAMPLE_RATE)

# Process sample through resampler
resampler = audiospeed.Resampler(sine_wave)

# Test each sample rate
for x in OUT_SAMPLE_RATES:
    mixer = audiomixer.Mixer(sample_rate=x, samples_signed=False)
    audio.play(mixer)
    mixer.play(resampler, loop=True)
    
    print(x, resampler.rate)
    time.sleep(1)
    
    mixer.stop_voice()
    audio.stop()
    mixer.deinit()
    del mixer

Notes:

• Some resampling rates slightly alter pitch. I'm chocking this up to the lack of linear interpolation.
• The property audiospeed.Resampler.rate exists as a getter primarily for testing purposes. This can be removed if desired.
• audiospeed.SpeedChanger is assigned a sample within the constructor. I decided to use the play/stop/playing paradigm instead to allow swapping samples. source could be added to the constructor of audiospeed.Resampler as an optional argument if desired. I decided to match the implementation of SpeedChanger by assigning the source only in the constructor.

For interest: @todbot @gamblor21 @kevinjwalters

[dhalbert]

@relic-se the build failure is due to a version change in some supporting software. If you rebase your PR to main latest or merge main, and then push that, the build should succeed.

[relic-se]

@dhalbert Thanks for the heads up. I was trying my hand at building the zephyr port locally to figure out the issue, but that's a much easier fix.

[dhalbert]

Build reports these errors, so it is something missing from the compile or link lists for zephyr:

usr/bin/ld: /home/runner/work/circuitpython/circuitpython/shared-module/audiocore/__init__.c:208:(.text.audiosample_must_match+0x96): undefined reference to `audiospeed_resampler_type'
/usr/bin/ld: /home/runner/work/circuitpython/circuitpython/shared-module/audiocore/__init__.c:223:(.text.audiosample_must_match+0xeb): undefined reference to `audiospeed_resampler_type'
/usr/bin/ld: /home/runner/work/circuitpython/circuitpython/shared-module/audiocore/__init__.c:223:(.text.audiosample_must_match+0x16c): undefined reference to `audiospeed_resampler_type'
/usr/bin/ld: /home/runner/work/circuitpython/circuitpython/shared-module/audiocore/__init__.c:225:(.text.audiosample_must_match+0x180): undefined reference to `audiospeed_resampler_set_sample_rate'

[relic-se]

@dhalbert I don't yet understand why this is happening. The references to shared-bindings/audiospeed/Resampler.h within shared-module/audiocore/__init__.c should be controlled using compile-time directives relying on CIRCUITPY_AUDIOSPEED which is defined on the following line: https://github.com/adafruit/circuitpython/pull/11057/changes#diff-be80dccee1b8ea2a741647a281b24e1e6c48b7e175584c4162cb81edda81af52R154

This should only be enabled within ports/raspberrypi/mpconfigport.mk and isn't available on any other ports.

I don't understand the Zephyr port enough to understand why it is ignoring these directives. I'll start by figuring out how to build it on my end. 😆

[dhalbert]

Looks good, thank you!