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Audio Synthesis with CircuitPython synthio Simple synthio Examples

Audio Synthesis with CircuitPython synthio

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by John Park and
Contributors:
published September 13, 2023, last updated October 15, 2024
posted in CircuitPython Programming/ MicroPython / CircuitPython Breakout Boards/ Amplifiers/Sound
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Beginner
Project guide

Simple synthio Examples

Let's get to some real-world examples! These are adapted from Tod Kurt's excellent CircuitPython Synthio Tricks page.

circuitpython_vco-square.png

Simple Note

Play Video: synthio basic example 1: single note
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# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import time
import board
import digitalio
import synthio

# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

synth = synthio.Synthesizer(sample_rate=44100)
audio.play(synth)

while True:
    synth.press(65)  # midi note 65 = F4
    time.sleep(0.5)
    synth.release(65)  # release the note we pressed
    time.sleep(2)
View on GitHub
circuitpython_vco-square.png
circuitpython_vco-square.png
circuitpython_vco-square.png
circuitpython_vco-square.png

Simple Chord

Play Video: synthio basic example 2: chords
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# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import time
import board
import digitalio
import synthio

# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

synth = synthio.Synthesizer(sample_rate=44100)
audio.play(synth)

while True:
    synth.press((65, 69, 72))  # midi note 65 = F4
    time.sleep(1)
    synth.release((65, 69, 72))  # release the note we pressed
    time.sleep(2)
View on GitHub
circuitpython_cv-mixer.png

Simple Chord with Mixer

Play Video: synthio basic example 3: mixer
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# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import time
import board
import digitalio
import audiomixer
import synthio

# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

mixer = audiomixer.Mixer(channel_count=1, sample_rate=22050, buffer_size=2048)
synth = synthio.Synthesizer(channel_count=1, sample_rate=22050)

audio.play(mixer)
mixer.voice[0].play(synth)
mixer.voice[0].level = 0.4

while True:
    synth.press((65, 69, 72))  # midi note 65 = F4
    time.sleep(0.5)
    synth.release((65, 69, 72))  # release the note we pressed
    time.sleep(0.5)
    mixer.voice[0].level = (mixer.voice[0].level - 0.1) % 0.4  # reduce volume each pass
View on GitHub
circuitpython_env-adsr.png

Amplitude Envelope

Play Video: synthio basic example 4: envelopes
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# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import time
import board
import digitalio
import audiomixer
import synthio

# for PWM audio with an RC filter
#import audiopwmio
#audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

mixer = audiomixer.Mixer(channel_count=1, sample_rate=22050, buffer_size=2048)

amp_env_slow = synthio.Envelope(
                                attack_time=0.2,
                                sustain_level=1.0,
                                release_time=0.8
)

amp_env_fast = synthio.Envelope(
                                attack_time=0.1,
                                sustain_level=0.5,
                                release_time=0.2
)


synth = synthio.Synthesizer(channel_count=1, sample_rate=22050, envelope=amp_env_slow)

audio.play(mixer)
mixer.voice[0].play(synth)
mixer.voice[0].level = 0.2

while True:
    synth.envelope = amp_env_slow
    synth.press(46)
    time.sleep(1.25)
    synth.release(46)
    time.sleep(1.25)

    synth.envelope = amp_env_fast
    synth.press(51)
    time.sleep(1.25)
    synth.release(51)
    time.sleep(1.25)
View on GitHub
circuitpython_vcf-lowpass-res.png

Filters

Play Video: synthio basic example 5: Filters
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# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import time
import board
import digitalio
import audiomixer
import synthio

# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

mixer = audiomixer.Mixer(channel_count=1, sample_rate=22050, buffer_size=2048)

amp_env_slow = synthio.Envelope(
                                attack_time=0.2,
                                sustain_level=1.0,
                                release_time=0.8
)

synth = synthio.Synthesizer(channel_count=1, sample_rate=22050, envelope=amp_env_slow)

# set up filters
frequency = 2000
resonance = 1.5
lpf = synth.low_pass_filter(frequency, resonance)
hpf = synth.high_pass_filter(frequency, resonance)
bpf = synth.band_pass_filter(frequency, resonance)

note1 = synthio.Note(frequency=330, filter=None)

audio.play(mixer)
mixer.voice[0].play(synth)
mixer.voice[0].level = 0.2

while True:
    # no filter
    note1.filter = None
    synth.press(note1)
    time.sleep(1.25)
    synth.release(note1)
    time.sleep(1.25)

    # lpf
    note1.filter = lpf
    synth.press(note1)
    time.sleep(1.25)
    synth.release(note1)
    time.sleep(1.25)

    # hpf
    note1.filter = hpf
    synth.press(note1)
    time.sleep(1.25)
    synth.release(note1)
    time.sleep(1.25)

    # bpf
    note1.filter = bpf
    synth.press(note1)
    time.sleep(1.25)
    synth.release(note1)
    time.sleep(1.25)
View on GitHub
circuitpython_keyboard-ctrl.png

MIDI Note Input

Play Video: synthio basic example 6: MIDI Note input
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# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import board
import digitalio
import audiomixer
import synthio
import usb_midi
import adafruit_midi
from adafruit_midi.note_on import NoteOn
from adafruit_midi.note_off import NoteOff

# note for ESP32-S2 boards, due to not enough available endpoints,
# to enable USB MIDI, create a "boot.py" with following in it, then power cycle board:
#  import usb_hid
#  import usb_midi
#  usb_hid.disable()
#  usb_midi.enable()
#  print("enabled USB MIDI, disabled USB HID")


# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

mixer = audiomixer.Mixer(channel_count=1, sample_rate=22050, buffer_size=2048)

midi = adafruit_midi.MIDI(midi_in=usb_midi.ports[0], in_channel=0)

amp_env_med = synthio.Envelope(
                                attack_time=0.05,
                                sustain_level=0.8,
                                release_time=0.2
)

synth = synthio.Synthesizer(channel_count=1, sample_rate=22050, envelope=amp_env_med)

note1 = synthio.Note(frequency=330, filter=None)

audio.play(mixer)
mixer.voice[0].play(synth)
mixer.voice[0].level = 0.2

while True:
    msg = midi.receive()
    if isinstance(msg, NoteOn) and msg.velocity != 0:
        print("noteOn: ", msg.note, "vel:", msg.velocity)
        note1.frequency = synthio.midi_to_hz(msg.note)
        synth.press(note1)
    elif isinstance(msg, NoteOff) or isinstance(msg, NoteOn) and msg.velocity == 0:
        print("noteOff:", msg.note, "vel:", msg.velocity)
        note1.frequency = synthio.midi_to_hz(msg.note)
        synth.release(note1)
View on GitHub
circuitpython_touch-ctrl.png

MIDI CC Input

Play Video: synthio basic example 7: MIDI CC input
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Copy Code 
# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import board
import busio
import digitalio
import audiomixer
import synthio
import usb_midi
import adafruit_midi
from adafruit_midi.note_on import NoteOn
from adafruit_midi.note_off import NoteOff
from adafruit_midi.control_change import ControlChange

# note for ESP32-S2 boards, due to not enough available endpoints,
# to enable USB MIDI, create a "boot.py" with following in it, then power cycle board:
#  import usb_hid
#  import usb_midi
#  usb_hid.disable()
#  usb_midi.enable()
#  print("enabled USB MIDI, disabled USB HID")


# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

mixer = audiomixer.Mixer(channel_count=1, sample_rate=22050, buffer_size=2048)

midi_channel = 1
uart = busio.UART(tx=board.TX, rx=board.RX, baudrate=31250, timeout=0.001)
midi_usb = adafruit_midi.MIDI(midi_in=usb_midi.ports[0], in_channel=0)
midi_uart = adafruit_midi.MIDI(midi_in=uart, in_channel=midi_channel-1)

amp_env_med = synthio.Envelope(
                                attack_time=0.05,
                                sustain_level=0.8,
                                release_time=0.2
)

synth = synthio.Synthesizer(channel_count=1, sample_rate=22050, envelope=amp_env_med)
# set up filters
filter_freq = 4000
filter_res = 0.5
filter_freq_lo = 100   # filter lowest freq
filter_freq_hi = 4500  # filter highest freq
filter_res_lo = 0.5    # filter q lowest value
filter_res_hi = 2.0    # filter q highest value
lpf = synth.low_pass_filter(filter_freq, filter_res)
note1 = synthio.Note(frequency=330, filter=lpf)

audio.play(mixer)
mixer.voice[0].play(synth)
mixer.voice[0].level = 0.2

def map_range(s, a1, a2, b1, b2):
    return b1 + ((s - a1) * (b2 - b1) / (a2 - a1))


while True:
    note1.filter = synth.low_pass_filter(filter_freq, filter_res)

    msg = midi_uart.receive() or midi_usb.receive()

    if isinstance(msg, NoteOn) and msg.velocity != 0:
        print("noteOn: ", msg.note, "vel:", msg.velocity)
        note1.frequency = synthio.midi_to_hz(msg.note)
        synth.press(note1)

    elif isinstance(msg, NoteOff) or isinstance(msg, NoteOn) and msg.velocity == 0:
        print("noteOff:", msg.note, "vel:", msg.velocity)
        note1.frequency = synthio.midi_to_hz(msg.note)
        synth.release(note1)

    elif isinstance(msg, ControlChange):
        print("CC", msg.control, "=", msg.value)
        if msg.control == 21:  # filter cutoff
            filter_freq = map_range(msg.value, 0, 127, filter_freq_lo, filter_freq_hi)
        elif msg.control == 22:  # filter Q
            filter_res = map_range(msg.value, 0, 127, filter_res_lo, filter_res_hi)
        elif msg.control == 7:  # volume
            mixer.voice[0].level = map_range(msg.value, 0, 127, 0.0, 1.0)
View on GitHub
circuitpython_lfo-triangle.png

LFO Pitch Bend

Play Video: synthio basic example 8: LFO pitch bend #adafruit
Download Project Bundle
Copy Code 
# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import board
import digitalio
import audiomixer
import synthio

# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

mixer = audiomixer.Mixer(channel_count=1, sample_rate=44100, buffer_size=4096)
synth = synthio.Synthesizer(channel_count=1, sample_rate=44100)

audio.play(mixer)
mixer.voice[0].play(synth)
mixer.voice[0].level = 0.1

lfo = synthio.LFO(rate=0.6, scale=0.05)  # 1 Hz lfo at 0.25%
midi_note = 52
note = synthio.Note(synthio.midi_to_hz(midi_note), bend=lfo)
synth.press(note)


while True:
    pass
View on GitHub

LFO Tremolo

circuitpython_lfo-sine.png

LFO Tremolo

Play Video: synthio basic example 9: LFO tremolo
Download Project Bundle
Copy Code 
# SPDX-FileCopyrightText: 2023 John Park and @todbot / Tod Kurt
#
# SPDX-License-Identifier: MIT

import time
import board
import digitalio
import audiomixer
import synthio

# for PWM audio with an RC filter
# import audiopwmio
# audio = audiopwmio.PWMAudioOut(board.GP10)

# for I2S audio with external I2S DAC board
import audiobusio

# I2S on Audio BFF or Amp BFF on QT Py:
# audio = audiobusio.I2SOut(bit_clock=board.A3, word_select=board.A2, data=board.A1)

# I2S audio on PropMaker Feather RP2040
power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
power.switch_to_output(value=True)
audio = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)

mixer = audiomixer.Mixer(channel_count=1, sample_rate=44100, buffer_size=4096)
synth = synthio.Synthesizer(channel_count=1, sample_rate=44100)

audio.play(mixer)
mixer.voice[0].play(synth)
mixer.voice[0].level = 0.2

lfo_tremolo = synthio.LFO(rate=0.8, scale=0.3, offset=0.7)

midi_note = 50
note1 = synthio.Note(synthio.midi_to_hz(midi_note), amplitude=lfo_tremolo)

synth.press(note1)


while True:
    print(lfo_tremolo.value)
    time.sleep(0.05)
View on GitHub

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