MIDI

MIDI is a hub for receiving, sending and filtering browser MIDI messages, and a library of functions for manipulating them.

The MIDI library aims to make it easy to attach physical instruments and controllers to web apps. As of June 2015 Chrome has native MIDI support. Joy! No other browser yet do.

MIDI properties

.request

A promise. Where MIDI is supported, the library requests access to the browser's midi API as soon as it loads. MIDI.request is the promise returned by navigator.requestMIDIAcess(), or where MIDI is not supported, MIDI.request is a rejected promise.

MIDI.request
.then(function(midi) {
    // Do something with midi object
})
.catch(function(error) {
    // Alert the user they don't have MIDI
});

Note that using the MIDI library you don't really need to touch the midi object. MIDI functions are available before the promise is resolved. For example, calling MIDI.on(query, fn) before this time will bind to incoming MIDI events when MIDI.request is resolved.

MIDI functions

.on(fn)

Registers a handler fn for all incoming MIDI events.

MIDI.on(function(data, time, port) {
    // Called for all incoming MIDI events.
});

.on(query, fn)

Registers a handler fn for incoming MIDI events that match query. A query can be expressed as a data array:

MIDI.on([145, 80], function(data, time, port) {
    // Called for Channel 2, NoteOn A4 messages.
});

MIDI.on([180, 1, 0], function(data, time, port) {
    // Called for Channel 5, Control Change 1 messages with value 0.
});

A query can alternatively be expressed as an object:

MIDI.on({ channel: 1, message: 'control' }, function(data, time, port) {
    // Called for all incoming MIDI Control Change
    // messages on channel 1.
});

MIDI.on({ message: 'control', data1: 7 }, function(data, time, port) {
    // Called for all incoming MIDI Control Change 7
    // messages on all channels.
});

Query objects can have one or more of the properties:

{
    channel: // number 1–16
    message: // string 'note', 'noteon', 'noteoff', 'control', 'pc', 'pitch', 'polytouch', 'channeltouch'
             // regexp, eg. /^note|^pitch/
    data1:   // number 0-127
             // string note name, eg. 'C#3'
    data2:   // number 0-127
}

Note that in order to optimise the speed of processing incoming MIDI events, filter queries are pre-sorted at the point of calling .on() and a listener tree is constructed. Incoming events are simply matched against the tree with a couple of lookups (very fast). This avoids filtering every incoming event against all queries (potentially slow) – but it also means that queries are not dynamic. Changing the values in a query after it has been passed to .on() will not alter the MIDI events that trigger fn.

.on(query, fn, args ... )

Function parameters passed into .on() following fn are passed to the handler as extra arguments. Use this to pass data to handlers:

function handler(data, time, port, data) {
    var bing = data.bing;    // 'bong'
}

MIDI.on([180, 1, 0], handler, { bing: 'bong' });

.once(query, fn)

Calls a handler fn once, on the next incoming MIDI event to match query. .once() can be used to implement a MIDI learn function:

function learnController(fn) {
    // Listen for next incoming MIDI controller message
    MIDI.once({ message: "control" }, function(message, time) {
        var query = message.splice();

        // Call the fn
        fn.apply(this, arguments);

        // Bind the fn to all values for this controller
        query.length = 2;
        MIDI.on(query, fn);
    };
}

.off(query, fn)

Removes an event handler from all MIDI events matching the query. If fn is not given, removes all handlers from events matching the query. If query is not given, removes the handler from all events.

.normalise(message, time)

Takes a MIDI message array and returns a Music JSON event array. Music JSON events have the form:

[timestamp, type, data ... ]

For MIDI events duration is 0. Note velocity, controller data and aftertouch data are normalised as floats in the range 0-1, while pitch bend data is normalised to floats representing semitones. For example:

MIDI.normalise([145,80,20], 1);    // [1, 'noteon', 80, 0.15748032]
MIDI.normalise([180,1,127], 2);    // [2, 'control', 1, 1]
MIDI.normalise([231,62,119], 3);   // [3, "pitch", 1.73409840]
MIDI.normalise([168,62,119], 4);   // [4, "aftertouch", 62, 0.93700787]

.normaliseEvent(e)

Takes a DOM MIDI event object and returns a Music JSON normalised event array. Equivalent to:

MIDI.normalise(e.data, e.receivedTime);

.isNote(message)

MIDI.isNote([145,80,20]);             // true

.isPitch(message)

MIDI.isPitch([145,80,20]);            // false

.isControl(message)

MIDI.isControl([145,80,20]);          // false

.toChannel(message)

Returns the MIDI channel of the message as a number 1-16.

MIDI.channel([145,80,20]);            // 2

.toType(message)

Returns type of message.

MIDI.message([145,80,20])             // 'noteon'

.normaliseNote(data)

Many keyboards transmit noteon with velocity 0 rather than noteoffs. normaliseNote converts noteon messages with velocity 0 to noteoff messages. A new array is not created – the existing array is modified and returned.

MIDI.normaliseNote([145,80,0]);       // [129,80,0]

.pitchToFloat(message, range)

Returns the pitch bend value in semitones. Range is the bend range up or down, in semitones. Where range is not given it defaults to 2.

MIDI.pitchToFloat([xxx,xx,xxx], 2);  // -1.625

.numberToNote(n)

Given a note number between 0 and 127, returns a note name as a string.

MIDI.numberToNote(66);                // 'F♯'

MIDI uses unicode symbols for accidentals ♭ and ♯.

.numberToOctave(n)

Given a note number between 0 and 127, returns the octave the note is in as a number.

MIDI.numberToOctave(66);              // 3

.numberToFrequency(n)

Given a note number n, returns the frequency of the fundamental tone of that note.

MIDI.numberToFrequency(57);           // 440

.numberToFrequency(n, reference)

The reference tuning is A = 440Hz by default. Pass in a value reference to use a different tuning.

MIDI.numberToFrequency(57, 442);      // 442

.frequencyToNumber(f)

NOT IMPLEMENTED

Given a frequency f, returns the note number whose fundamental harmonic corresponds to that frequency.

MIDI.frequencyToNumber(440);          // 57

.frequencyToNumber(f, reference)