hello_midi

Uses rtmidi, rimd and midir libs to read MIDI and play it. Tested on Mac OS X using SimpleSynth and the public domain JS Bach Goldberg variations.

Usage

We recommend downloading the JS Bach Goldberg Variations from https://www.opengoldbergvariations.org/.

cargo run ~/Documents/Goldberg_Variations.mid

We recommend listening to Fredrik Johansson's MIDI repository, an excellent, extensive body of work! Bravo!

Building on Raspbian

You need to install libsound2.

sudo apt-get install libasound2-dev

At this point you can then build the alsa crate for rust on your Pi.

Misc OS Configs

Mac OS X

• Install SimpleSynth according to https://github.com/wbsoft/frescobaldi/wiki/MIDI-playback-on-Mac-OS-X

Raspbian

Playing MIDI

Hook up a speaker to your Pi, then:

sudo apt-get install wildmidi
wildmidi Bach_Party.mid

Virtual MIDI

Required reading: http://sandsoftwaresound.net/qsynth-fluidsynth-raspberry-pi/

Key insight: you need to start fluidsynth as a server, allow MIDI input, connect it to your ALSA sound device on the Pi, and then correctly select the device number when starting this application:

fluidsynth -a alsa -i /usr/share/sounds/sf2/FluidR3_GM.sf2 --server
aconnect -lio   #  and COUNT the number of MIDI related devices
cargo run ~/Goldberg_Variations.mid 1  # if fluidsynth is the only virtual midi device on your pi, it should have ID 1.  see `aconnect -lio`

Helper command -- play a midi file to your speaker using fluidsynth:

fluidsynth -a alsa -n -i /usr/share/sounds/sf2/FluidR3_GM.sf ~/Goldberg_Variations.mid

See MIDI devices:

aconnect -lio

See sound cards:

aplay -l

Raspbian MIDI to mp3 conversion

Install mplayer to get going quickly with playing an mp3 file to a bluetooth speaker.

You can use a combination of timidity and lame to convert MIDI files to mp3.

sudo apt-get install mplayer timidity lame

timidity MIDI_sample.mid -Ow -o - | lame - -b 64 sample.mp3

mplayer sample.mp3

MIDI sample data

We ran rimd test bin against the Goldberg Variations and found the expected header data, as well as plenty of Note On events.

% cargo run --bin test # rimd

Reading: /Documents/Goldberg_Variations.mid
format: multiple track
tracks: 2
division: 480

1: Track, copyright: [none], name: [none]
events:
  time: 0	Meta Event: Time Signature: 3/4, 24 ticks/metronome click, 8 32nd notes/quarter note
  time: 0	Meta Event: Key Signature, 1 sharps/flats, Major
  time: 0	Meta Event: Set Tempo, microseconds/quarter note: 833333
  ...
  time: 0	Note On: [79,80]	channel: Some(0)
  time: 479	Note On: [79,0]	channel: Some(0)
  time: 480	Note On: [79,80]	channel: Some(0)
  time: 959	Note On: [79,0]	channel: Some(0)
  ...
  time: 3715	Note On: [67,0]	channel: Some(0)
  time: 3720	Note On: [69,80]	channel: Some(0)
  time: 3778	Note On: [67,80]	channel: Some(0)
  time: 3784	Note On: [69,0]	channel: Some(0)

We can see by reading http://www.onicos.com/staff/iz/formats/midi-event.html that most of these are "Channel 1 Note On".

Notes on Midi Time Management

MIDI Note On / Note Off events are ordered in time. Each event contains a delta_time (vtime) field representing the time elapsed since the last event.

In most cases, you can use the headers/metadata at the beginning of the file to establish a simple relationship between microseconds and "ticks" of the MIDI score.

From rimd documentation in meta.rs:

    /// The parameter `clocks_per_tick` is the number of MIDI Clocks per metronome tick.

    /// Normally, there are 24 MIDI Clocks per quarter note.
    /// However, some software allows this to be set by the user.
    /// The parameter `num_32nd_notes_per_24_clocks` defines this in terms of the
    /// number of 1/32 notes which make up the usual 24 MIDI Clocks
    /// (the 'standard' quarter note).  8 is standard
    pub fn time_signature(numerator: u8, denominator: u8, clocks_per_tick: u8, num_32nd_notes_per_24_clocks: u8) -> MetaEvent {
        MetaEvent {
            command: MetaCommand::TimeSignature,
            length: 4,
            data: vec![numerator,denominator,clocks_per_tick,num_32nd_notes_per_24_clocks],
        }
    }

Open Goldberg Variations JS Bach midi appears to support the standard timing when loaded:

vtime 0 event time: 0	Meta Event: Time Signature: 3/4, 24 ticks/metronome click, 8 32nd notes/quarter note
  ...snip...
  vtime 0 event time: 0	Meta Event: Set Tempo, microseconds/quarter note: 833333

A more detailed specification of the byte-level MIDI delta time (vtime) field can be found here:

https://www.csie.ntu.edu.tw/~r92092/ref/midi/

Using SoundFlower to record MIDI

Not strictly related to the build, but...

This is helpful for redirecting your successful playback of MIDI to a sound file that you're recording.

https://github.com/mattingalls/Soundflower/releases/tag/2.0b2

Acknowledgements

Bach's Goldberg Variations are available under Creative Commons License here.

Big thanks to midir library.

Big thanks to rimd library.

Big thanks to rtmidi library.

Thank you to fluidsynth, which allowed us to send MIDI output to our audio device.