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beet.js

Polyrhythmic Sequencer library for Web Audio API.

The sequencer can have multiple layers where each layer has a different step count. This feature allows the user to create complex polyrhythms and euclidean rhythms using a simple api.

Installation

You can install beet from npm.

npm install beet.js

Or grab the latest version from build folder and include it in your html.

<script src='beet.min.js'></script>

Example Usage

var context = new AudioContext();

// initialize beet
var beet = new Beet({
  context: context,
  tempo: 100
});

// create a euclidean pattern - 5 pulses distrubted in 7 steps
var pattern = beet.pattern(5,7);

// create a beet layer - pass it the pattern and a callback
var layer = beet.layer(pattern, callback);

function callback(time){
  var osc = context.createOscillator();
  osc.connect(context.destination);
  osc.start(time);
  osc.stop(time + 0.1);
}

// add the layer
beet.add(layer);

// start the sequencer
beet.start();

API

Beet

new Beet(opts)

Beet constructor. Returns a new instance of beet.

Parameters

beet.start(time)

Starts the sequencer after a given time in seconds.

Parameters

beet.stop(time)

Stops the sequencer after a given time in seconds and resets the current step number.

Parameters

beet.pause(time)

Pauses the sequencer after a given time in seconds but keeps the current step number.

Parameters

beet.add(layer(s))

Adds a given beet.layer to the list of layers to play. Can also be used with multiple layers. beet.add(layer1, layer2)

Parameters

beet.remove(layer)

Removes a given beet.layer from the list of layers to play.

Parameters

Pattern

The pattern method will return a pattern object based on the provided values. If pulses and steps are passed in as numbers, an equally distributed pattern will be generated and returned. Alternatively, you can use a custom pattern string. For example '1000101010'.

beet.pattern(pulses, steps)

Returns a pattern object containing a bjorklund sequence with equally distributed number of pulses over steps.

Parameters

example

var pattern = beet.pattern(3, 7);
// a pattern object containing a sequence as below
// '1010100'

var pattern2 = beet.pattern(4);
// a pattern object with a sequence as below
// '1111'

beet.pattern(patternString)

Returns a pattern object containing a the custom pattern. This can be used to generated custom sequences when neccessary.

Parameters

example

var pattern = beet.pattern('100010010');
var pattern2 = beet.pattern('10001111');

.update(pulses, steps)

Updates the pattern object with the new values. You can also update the values directly. See example below.

Parameters

example

var pattern = beet.pattern(2, 5);
pattern.update(5,8); // updates the pattern to '10100'

// you can also set the values separately
pattern.pulses = 4;
pattern.steps = 8;

.shift(offset)

Shifts the sequence by the offset and returns the pattern object.

Parameters

example

var pattern = beet.pattern(1, 4); // returns '1000'
pattern.shift(1) // updates the sequence to '0100'

Layer

layer(pattern, onCallback, offCallback)

Creates a beet.layer object and returns it.

Parameters

example

var pattern = beet.pattern(1, 4); // returns '1000'
var layer = beet.layer(pattern, on, off);
// on will be called on 1
// off will be called on 0's

Callback format

The callbacks are functions that will be called from the scheduler. The functions will be called with time, step and timeFromScheduled parameters. You can use the time parameter for web audio methods. step can be used to change audio behaviour according to the current step. timeFromScheduled is a value in seconds which corresponds to the time it will take for an audio event to occur from the time it was scheduled (time - context.currentTime). It can be used to schedule JS events using setTimeout.

example

function callback (time, step, timeFromScheduled) {
    var osc = context.createOscillator();
    osc.connect(context.destination);
    if(step === 1){
      osc.frequency.value = 880;
    }
    osc.start(time);
    osc.stop(time + 0.2);
    setTimeout(function(){
      // trigger some js event such as animation - will be synced to the audio
    }, timeFromScheduled * 1000);
}

Play/Pause/Stop layers

You can play and pause individual layers using:

var pattern = beet.pattern(1, 4); // returns '1000'
var layer = beet.layer(pattern, on, off);
layer.play()
layer.pause()
layer.stop()

Utils

Beet comes with a series of useful utilities for web audio api. These might me moved to a separate module in the future as these are not specific to beet's functionality. But for now, features will be added gradually.

.envelope(audioparam, now, opts)

Applies an envelope to the audio param given a series of options.

Parameters

example

var osc = context.createOscillator();
var gain = context.createGain();
osc.connect(gain);
gain.connect(context.destination);

beet.utils.envelope(gain.gain, time, {
  start: 0,
  peake: 1.0,
  attack: 0.1,
  decay: 0.2,
  sustain: 0.8,
  release: 0.5
});

osc.start(time);
osc.stop(time + 2);

.load(path, success, failure, context)

Loads an audio file for a given path and returns a decoded AudioBuffer object.

Parameters

example

beet.utils.load('path/to/file.wav', function(buffer){
  // do something with the buffer
}, failureHandler, context);

.mtof(midi_note)

Converts a give midi note to a frequency value in hz.

Parameters

example

beet.utils.mtof(69); // will return 440 for A4

.ntof(note_name)

Converts a given note name to a frequency value in hz.

Parameters

example

beet.utils.ntof('a4'); // will return 440 for A4

.mtop(midi_note)

Converts a given midi note to a value representing the playbackRate.

Parameters

example

beet.utils.mtop(60); // will return 1 for C4 - meaning the sample will be played in the original speed
beet.utils.mtop(72); // will return 2 for C3
beet.utils.mtop(48); // will return 0.5 for C2