#music #midi #synthesizer #synth


Enables creation of live MIDI synthesizer software

13 releases

0.3.2 Dec 31, 2023
0.2.1 Nov 13, 2023
0.1.5 Jul 13, 2023
0.1.4 Feb 2, 2023
0.1.2 Dec 28, 2022

#81 in Audio

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745 lines


Live performance synthesizer library

This crate assembles and integrates code from the midir, midi-msg, and cpal crates to enable the easy creation of live synthesizer software using fundsp for sound synthesis.

Using the crate involves setting up the following:

  • An input thread to monitor MIDI events
  • An output thread generating sounds that correspond to those events
  • A table of fundsp sounds for the output thread to employ
  • A SegQueue that enables those threads to communicate

Putting these pieces together yields the following introductory example program:

use std::sync::{Arc, Mutex};

use crossbeam_queue::SegQueue;
use crossbeam_utils::atomic::AtomicCell;
use midi_fundsp::{
    io::{get_first_midi_device, start_input_thread, start_output_thread},
use midir::MidiInput;
use read_input::{shortcut::input, InputBuild};

fn main() -> anyhow::Result<()> {
    let mut midi_in = MidiInput::new("midir reading input")?;
    let in_port = get_first_midi_device(&mut midi_in)?;
    let midi_msgs = Arc::new(SegQueue::new());
    let quit = Arc::new(AtomicCell::new(false));
    start_input_thread(midi_msgs.clone(), midi_in, in_port, quit.clone());
    start_output_thread::<10>(midi_msgs, Arc::new(Mutex::new(options())));
    input::<String>().msg("Press any key to exit\n").get();

The first four lines set up:

  • A handle to the first MIDI input device it finds
  • A messaging queue to connect the input and output threads
  • A flag to instruct the threads to quit

The next two lines call start_input_thread() and start_output_thread() to start the corresponding threads. The table of fundsp sounds comes from midi_fundsp::sounds::options(), but a user can easily assemble their own custom table of sounds as well.

Once the threads start, the program continues until the user enters a key, handling any incoming MIDI events as they arrive.

Other example programs show how to send different sounds to the left and right stereo channels and how to change the selection of synthesizer sound and MIDI input device while running.


  • Always compile with --release. Sound quality is poor when compiled with --debug.
  • The following MIDI messages are currently supported:
    • Note On
    • Note Off
    • Pitch Bend
    • Program Change
      • Program change numbers correspond to indices in the ProgramTable
      • These can originate either from a MIDI input device or from software
    • All Notes Off
    • All Sound Off
  • See CHANGELOG.md for updates.


  • Thank you to the authors of fundsp, midir, midi-msg, and cpal, who made it possible and practical for me to create this crate.
  • Special thanks to Sami Perttu, author of fundsp, for help resolving some technical issues and for incorporating pull requests into fundsp that made this crate possible.


Licensed under either of

at your option.


I am very interested in receiving contributions to this library. Here are types of contributions I envision, and how I would like contributors to proceed:

  • Creating additional synthesizer sounds
    • Add a function with type signature Fn(&SharedMidiState) -> Box<dyn AudioUnit64> to sounds.rs. Add your function and a suitable description to the table generated by options() in that same file. Then make a pull request to include it.
  • Handling additional MIDI messages
    • Open an issue describing the MIDI message you would like to handle, and conceptually speaking how you would like to handle it in the context of this library.
    • From there, we will discuss the best way forward.
  • Other ideas
    • Open an issue describing your idea, and we will discuss it from there.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.


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