I’ve been collecting bookmarks for interesting Arduino audio projects for a while now, and having now played with the XIAO SAMD21 I started looking back over my list for other things to try. One thing that occurred to me is that there are a now a number of more powerful audio frameworks available for a range of microcontrollers, so in this post I’m doing an introductory “look see” at some of them, largely as “notes to self” to come back to them for some more detailed projects in the future.
Note: Many of these require a 32-bit processor, which is one of the reasons I’ve not looked at them so far.
Warning! I strongly recommend using old or second hand equipment for your experiments. I am not responsible for any damage to expensive instruments!
If you are new to microcontrollers, see the Getting Started pages.
Mozzi
I’ve spent quite a bit of time with Mozzi of course, the synthesis library for Arduino that supports a large range of microcontrollers, including the “original” 8-bit Arduino ATmega328P, so I won’t go over that again here.
For a starting point with Mozzi, see: Arduino PWM MIDI Synthesis with Mozzi. For using Mozzi on a 32-bit SAMD processor, there is more here and here.
But Mozzi isn’t the only game in town, especially if we’re expanding out to 32-bit microcontrollers.
The Arduino Sound Library
https://www.arduino.cc/reference/en/libraries/arduinosound/
This is an official Arduino library that supports SAMD21 based microcontrollers using an I2S digital to analog converter. It is designed for the MKR series of official Arduino boards.
Interestingly it appears to only support I2S audio devices for sound input and output. That seems like a little bit of a missed opportunity to me in that the SAMD21 has a built-in DAC, but I guess analogWrite() deals with access to the DAC relatively easily.
It is designed for official Arduino SAMD architecture boards – so those in the MKR series. It might work on other SAMD architecture boards, I haven’t looked into it in detail.
Phil Schatzmann’s Arduino Audio Tools
https://github.com/pschatzmann/arduino-audio-tools
This is a suite of open source code for audio stream processing, providing a range of audio sources (e.g. microphones, Internet streams, files, sensors, and so on) and sinks (e.g. DACs, PWM audio, MP3, codecs, audio modules, etc).
It can be used to build audio players, processors, effects, file processors, audio visualisers, networked audio tools, and so on.
I believe it supports the following microcontroller architectures:
- ESP32 (S and C variants)
- ESP8266
- RP2040 (MBED and non-MBED)
- AVR
- STM32
- SAMD
It supports several audio output boards too, including: ESP32-A1S based boards (ES8388 or AC101 codecs); VS1053 modules; and WM8960 modules.
I believe this is a library for audio processing, not necessarily audio synthesis.
Marcel Licence’s ML Synth Tools
https://github.com/marcel-licence/ML_SynthTools
This is a comprehensive synth library for producing synthesizers, organs and effects. Most of the code is open source, but there are certain key elements that are provided only in pre-built library form.
It provides libraries for the following microcontrollers:
- ESP32
- ESP8266
- XIAO SAMD21
- Teensy 4.1
- Daisy Seed
- Raspberry Pi Pico RP2040
- STM32F407
As well as the synthesizer core oscillators there are modules for arpeggiators, effects, meters, scopes, and MIDI file playing. Here are some example builds using the library:
- ML Organ (all platforms): https://github.com/marcel-licence/ml_synth_organ_example
- SAMD21 Synth: https://github.com/marcel-licence/samd21_mini_synth
- ML Synth (all platforms): https://github.com/marcel-licence/ml_synth_basic_example
- ESP32 FM synth: https://github.com/marcel-licence/esp32_fm_synth
- ESP32/RP2040 e-piano: https://github.com/marcel-licence/ml_epiano_example
Although it isn’t fully open source, this non-the-less looks like it would be worth taking a more detailed look. The provided videos of Marcel playing are particularly excellent.
MIDI Controller Libraries
There are a number of Arduino libraries for building MIDI controllers. Here are a selection of some that I’ve found so far.
OpenDesk MIDI Platform – https://github.com/shanteacontrols/OpenDeck
This is a set of firmware and two official PCB designs for MIDI controllers. In addition to the official boards, it also supports many microcontrollers, including:
- Arduino Mega 2560
- Arduino Nano 33 BLE
- Raspberry Pi Pico
- XIAO RP2040
- Teensy++ 2.0
And many others. It includes a web-based configuration utility for defining the MIDI commands for the controls. Official boards are available on Tindie and you can read more about them here: https://shanteacontrols.com/.
It supports a range of buttons, encoders, potentiometers, force sensitive resistors, certain touchscreens and can provided feedback using LEDs and displays.
Control Surface – https://github.com/tttapa/Control-Surface
This is a general purpose library for building MIDI input and output control devices. It supports a wide range of microcontrollers, including:
- AVR (Uno, Mega, Leonardo).
- Arduino Nano Every and 33.
- Teensy.
- ESP8266
- ESP32
- Raspberry Pi Pico
It supports a range of MIDI transports, including serial, USB, “direct serial” (using Hairless MIDI) and MIDI BLE. It also supports a range of buttons, potentiometers, rotary encoders, switches, keyboard matrices, and so on and can provide visual feedback using a range of LEDS and displays. It has built-in support for multiplexers, shift registers and LED drivers.
It includes a huge number of example projects to browse.
MIDIPal – https://github.com/pichenettes/midipal
This is a “MIDI Swiss Army Knife” that, with the additional of a display and rotary encoder, can provide a wide range of MIDI processing functions. It includes an editor application for programming MIDI filters.
This is a “native” AVR application, not for the Arduino environment.
Notes and Volts MIDI Controller – https://www.notesandvolts.com/2016/04/arduino-midi-controller-buttons.html
This is provided for completeness as it is a fairly common codebase for people to find and use with an Arduino. It supports a range of potentiometers and buttons and makes the task of configuring them as a MIDI control device relatively straight forward.
Closing Thoughts
As I say, this post is really almost a bit of a “to-do list” of things that look interesting and that I might try to take a more detailed look at, at some point.
If you have experience of any of these frameworks or libraries; or have suggestions of others that might be worth a look, do let me know in the comments!
Kevin
Simple DIY Electronic Music Projects 
Thank you! This is a very helpful list.
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