Drone synthing using two knobs to control three voices in synthio with optional echo effect in CircuitPython

two_pot_drone_synth.py

# two_pot_drone_synth.py -- Use two knobs to control three voices in synthio
#                           with optional echo effect
# 25 Nov 2024 - @todbot / Tod Kurt
# video demo: https://www.youtube.com/watch?v=xEmhk-dVXqQ
# original simpler version:
# https://gist.github.com/todbot/53bfa7333ac7c1fcff8eaf0f547556ff

import time, random
import board, keypad, analogio
import audiopwmio, audiomixer, synthio
import ulab.numpy as np

sample_rate=36000  # higher sampling rate means faster knob response 

# set up input devices
keys = keypad.Keys( (board.GP4, board.GP8), value_when_pressed=False, pull=True)
knob1 = analogio.AnalogIn(board.GP26)
knob2 = analogio.AnalogIn(board.GP27)

# set up audio out. Using mixer reduces glitches
audio = audiopwmio.PWMAudioOut(board.GP15)
mixer = audiomixer.Mixer(voice_count=1, sample_rate=sample_rate, channel_count=1,
                         bits_per_sample=16, samples_signed=True, buffer_size=2048)
synth = synthio.Synthesizer(sample_rate=sample_rate)
audio.play(mixer)

# try to load up echo effect, if not available no worries
try:
    import audiodelays
    effect = audiodelays.Echo( max_delay_ms=600, delay_ms=600,
                               decay=0.7, mix=0.4,  freq_shift=False,
                               buffer_size=2048, sample_rate=sample_rate )
    mixer.voice[0].play(effect)
    effect.play(synth)
except:
    mixer.voice[0].play(synth)  # if we don't have delay

# configure our synthesizer and set it going
lfo = synthio.LFO(rate=5)
amp_env = synthio.Envelope(attack_time=0.5, release_time=0.5)
wave_saw = np.linspace(30000, -30000, num=512, dtype=np.int16)  # max is +/-32k but gives us headroom
# need to lower amplitude or get clipping when delays are active
note1 = synthio.Note(frequency=100, waveform=wave_saw, amplitude=0.5, envelope=amp_env)
note2 = synthio.Note(frequency=100, waveform=wave_saw, amplitude=0.5, envelope=amp_env)
note3 = synthio.Note(frequency=100, waveform=wave_saw, amplitude=0.5, envelope=amp_env)
synth.press((note1,note2, note3))

f = 0.7   # for simple knob filtering
k1, k2 = 0, 0
last_print_time = 0
while True:
    # handle button presses
    if key := keys.events.get():
        print("key:",key)
        if key.key_number == 0:  
            if key.pressed:
                note1.bend = lfo
            else:
                note1.bend = 0
        if key.key_number == 1:
            if key.pressed:
                synth.release_all()
            else:
                synth.press((note1,note2))
        
    # simple knob filtering because noisy ADCs
    k1 += int((knob1.value - k1) * f)
    k2 += int((knob2.value - k2) * f)

    # update the drone voices' pitches
    note1.frequency = synthio.midi_to_hz( k1 / 512 )
    note2.frequency = synthio.midi_to_hz( k2 / 512 )
    note3.frequency = note2.frequency*1.005  # detune for phatness
    
    time.sleep(0.001)
    
    if time.monotonic() - last_print_time > 0.2:
        last_print_time = time.monotonic()
        print("notes %4.1f %4.1f" % (k1/512, k2/512))  # a little debug info