fade between different drum loops on QTPy RP2040 or Xiao RP2040 in CircuitPython

beatfader_demo.py

"""
beatfader_demo.py -- fade between different drum loops
10 Jun 2024 - @todbot / Tod Kurt

originally from
https://github.com/todbot/circuitpython-tricks/blob/main/larger-tricks/beatfader.py

Demonstrate how to play WAVs via PWM audio

Functions, designed for QTPy RP2040 or Xiao RP2040:
- knob on A0 -- master "fader" between different playing WAV loops
- PWM audio on MOSI

To use:
- Copy the "beatfader_wavs" directory at this URL to the CIRCUITPY drive
https://github.com/todbot/circuitpython-tricks/tree/main/larger-tricks/beatfader_wavs
- Or use your own loops, prefer 22050 kHz sample rate and up to around 10 or so

"""
import os, time
import board, analogio
import audiocore, audiomixer, audiopwmio

wav_dir = "/beatfader_wavs"

def load_wavs(wav_dir):
    """ find all the WAVs in a given dir, use the first WAV found as model
    for what the other WAVs should be, and returns filenames, sample_rate, and
    channel_count"""
    some_wav_fnames =[]
    for fname in sorted(os.listdir(wav_dir)):  # sort so we have known order
        if fname.lower().endswith('.wav') and not fname.startswith('.'):
            some_wav_fnames.append(wav_dir+"/"+fname)
    print("some_wav_fnames:", some_wav_fnames)
    
    # determine their sample rate and channel count of first sample,
    # use it to verify all other samples match
    with audiocore.WaveFile(some_wav_fnames[0]) as wav:
        sample_rate = wav.sample_rate
        channel_count = wav.channel_count
        print("sample_rate", sample_rate, "chan_cnt", channel_count)

    good_wav_fnames = []  # these are the good ones
    for i, fname in enumerate(some_wav_fnames):
        with audiocore.WaveFile(some_wav_fnames[i]) as wav:
            if wav.sample_rate != sample_rate or wav.channel_count != channel_count:
                print("bad WAV file:", fname)
            else:
                good_wav_fnames.append(fname)

    return good_wav_fnames, sample_rate, channel_count


wav_fnames, sample_rate, channel_count = load_wavs(wav_dir)

print("found wavs:", wav_fnames, "with sample=rate",
      sample_rate, "channel_count", channel_count)

audio = audiopwmio.PWMAudioOut(board.MOSI)
mixer = audiomixer.Mixer(sample_rate = sample_rate,
                         voice_count = len(wav_fnames),
                         channel_count = channel_count,
                         bits_per_sample=16, samples_signed=True,
                         buffer_size=2048)
audio.play(mixer)

knob = analogio.AnalogIn(board.A0)
        
# start all WAVs playing, in sync, but quiet
for i, fname in enumerate(wav_fnames):
    wave = audiocore.WaveFile(fname)
    mixer.voice[i].level = 0.0      # start quiet
    mixer.voice[i].play(wave, loop=True) # start playing


num_wavs = len(wav_fnames)
last_time = 0
fader_n = num_wavs * 0.8  # amount of overlap
fader_m  = 1/(num_wavs-1) # size of slice

while True:
    knob_pct = knob.value / 65535 
    for i,voice in enumerate(mixer.voice):
        voice.level = min(max( 1 - (fader_n * (knob_pct - fader_m*i))**2, 0), 1)