Using AudioMixer and I2S in CircuitPython to fade up and down loops

audiomixer_demo_i2s.py

# audiomixer_demo_i2s.py -- show how to fade up and down playing loops
# Code based on that of https://github.com/todbot/circuitpython-tricks/blob/main/larger-tricks/audiomixer_demo.py
# where you can also find the WAV files used
# 30 Nov 2022 - @todbot / Tod Kurt

import time
import board
import audiocore
import audiomixer
import audiobusio

i2s_bclk = board.GP9   # BCK on PCM5102 I2S DAC (SCK pin to Gnd)
i2s_wsel = board.GP10  # LCLK on PCM5102
i2s_data = board.GP11  # DIN on PCM5102
num_voices = 2

audio = audiobusio.I2SOut(bit_clock=i2s_bclk, word_select=i2s_wsel, data=i2s_data)

mixer = audiomixer.Mixer(voice_count=num_voices, sample_rate=22050, channel_count=1,
                         bits_per_sample=16, samples_signed=True)
audio.play(mixer) # attach mixer to audio playback

print("audio is now playing")

# set some initial levels
mixer.voice[0].level = 1.0  # drums on
mixer.voice[1].level = 0.0  # synth off

# load wav and start drum loop playing
wave0 = audiocore.WaveFile(open("wav/drumsacuff_22k_s16.wav","rb"))
mixer.voice[0].play( wave0, loop=True )

# load wav and start synth loop playing
wave1 = audiocore.WaveFile(open("wav/snowpeaks_22k_s16.wav","rb"))
mixer.voice[1].play( wave1, loop=True )

time.sleep(1.0)  # let drums play a bit

# fade each channel up and down
up_down_inc = 0.01
while True:
    print("voice 0 level=%1.2f" % mixer.voice[0].level)
    mixer.voice[1].level = min(max(mixer.voice[1].level + up_down_inc, 0), 1)
    mixer.voice[0].level = min(max(mixer.voice[0].level - up_down_inc, 0), 1)
    if mixer.voice[0].level == 0 or mixer.voice[1].level == 0:
        up_down_inc = -up_down_inc
    time.sleep(0.1)

Demo of the above code on a Raspberry Pi Pico and PCM5102 I2S DAC

audiomixer_demo_i2s.mp4