TuriSc / Pico-Sequencer-Synth

A polyphonic, multitimbral DDS (Direct Digital Synthesis) library for Raspberry Pi Pico with a sequencer supporting up to 8 channels

Pico Sequencer Synth

A polyphonic, multitimbral DDS (Direct Digital Synthesis) library for Raspberry Pi Pico, equipped with a sequencer supporting up to 8 channels.

Demo video: YouTube link

Features

• I²S or PWM audio output
• Available waveforms: NOISE, SQUARE, SAW, TRIANGLE, SINE, WAVE (custom waveform)
• ADSR amp envelope
• Polyphony up to 8 voices, each one with individual waveform, ADSR, and volume settings
• 44.100 kHz default sample rate
• Multitrack sequencer able to start and stop playback of multiple (non-concurrent) sequences
• A note name to pitch map, covering notes from B0 to D#8
• Chiptune-ready!

Usage

A full example program is included. Please see example/example.c.

To specify which audio output to use, leave uncommented only one of the two definitions in your CMakeLists.txt

target_compile_definitions(${PROJECT_NAME} PRIVATE
        # USE_AUDIO_PWM=1
        USE_AUDIO_I2S=1
    )

A note about PWM audio

The audio quality of the PWM output is greatly inferior to the I²S one. It's also very noisy if unfiltered, and for this reason you might want to pair it with a DAC circuit to smooth the signal. There are several designs that will work, but my research led me to the one I used for Dodepan, which also provides some noise filtering and DC offset removal.

Credits

This library is the C port of a C++ demo by Pimoroni, adapted to output audio via I²S or PWM. The original depencency of 'Pico Extras' SDK libraries has been removed and I²S functionality is now provided by a PIO-driven I²S driver based on the work of Ricardo Massaro.

Version history

• 2024.01.13 - Initial release