Adafruit CircuitPython 9.2.6 on 2025-03-23; Raspberry Pi Pico 2 with rp2350a
Adafruit CircuitPython 9.2.6 on 2025-03-23; Raspberry Pi Pico with rp2040

"""
filter Q over 1.41 causes glitches in the filter at certain frequency
"""

import time, board, synthio, audiobusio, audiomixer

SAMPLE_RATE = 44100
BUFFER_SIZE = 2048
i2s_bck_pin = board.GP20
i2s_lck_pin = board.GP21
i2s_dat_pin = board.GP22

audio = audiobusio.I2SOut(bit_clock=i2s_bck_pin, word_select=i2s_lck_pin, data=i2s_dat_pin)
mixer = audiomixer.Mixer(sample_rate=SAMPLE_RATE, channel_count=2, buffer_size=BUFFER_SIZE)
synth = synthio.Synthesizer(sample_rate=SAMPLE_RATE, channel_count=2)
audio.play(mixer)
mixer.voice[0].play(synth)

midi_notes = [ 49,  # glitch near 170 & 150 Hz
               37,  # glitch near 100, 70, & 60 Hz
               36,  # gitch near 70 & 60 Hz
               42,  # glitch near 100 Hz
               47,  # glitch near 120 Hz
              ]
while True:
    for n in midi_notes:
        midi_note_f = synthio.midi_to_hz(n)
        note = synthio.Note(midi_note_f)
        note.filter = synthio.BlockBiquad(synthio.FilterMode.LOW_PASS,
                                          frequency=200, Q=1.5)
        synth.press(note)
        for f in range(21):  # modulate the filter down by hand to find glitches
            filter_freq = 200 - (10*f)
            print("Q: %.2f filter freq: %3d note freq: %3.2f" %
                  (note.filter.Q, filter_freq, midi_note_f))
            note.filter.frequency = filter_freq
            time.sleep(0.3)        
        synth.release(note)