This repository contains my adaptation of the great little software synthesizer pico_synth_ex by Ryo Ishigaki (ISGK Instruments).
The synth is tetraphonic and boasts two oscillators with descending sawtooth and square waveforms, a customizable filter with resonance control and cutoff modulation, a Decay-Sustain amp envelope, and an LFO for added modulation possibilities.
This version of the synth can output audio via I²S interface, unlike the original program, which only used PWM. A previous version served as the audio engine for my toy keyboard Picophonica.
An example program is included. Please see example/example.c.
To specify which audio output to use, enable only one of the two definitions in your CMakeLists.txt
target_compile_definitions(${PROJECT_NAME} PRIVATE
# USE_AUDIO_PWM=1
USE_AUDIO_I2S=1
)The audio quality of PWM output is greatly inferior to I²S audio. 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.
This library is released under a MIT-0 license (see LICENSE), with the exception of the I²S driver, based on the work of Ricardo Massaro, released under a MIT License (see sound_i2s/LICENSE for details).
Original code: pico_synth_ex by Ryo Ishigaki (ISGK Instruments). Released in the public domain.
- 2024-03-04 - First release