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.

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>

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();

Beet constructor. Returns a new instance of beet.

• opts (required) - an object containing the initialisation options
  • context (required) - an instance of AudioContext
  • tempo (optional) - speed in BPM - defaults to 120

Starts the sequencer after a given time in seconds.

• time - a number in seconds - defaults to 0

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

• time (optional) - a number in seconds - defaults to 0

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

• time (optional) - a number in seconds - defaults to 0

Adds a given beet.layer to the list of layers to play.

• layer (Required) - a beet.layer object.

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

• layer (Required) - a beet.layer object.

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

• pulses (required) - number of pulses (active steps) in the sequence
• steps (optional) - number of steps in the sequence - value of pulses will be used steps is not specified.

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'

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

• pulses (required) - number of pulses (active steps) in the sequence.
• steps (optional) - number of steps in the sequence. value of pulses will be used steps is not specified.

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;

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

• offset (required) - number of steps to shift the sequence by

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

Creates a beet.layer object and returns it.

• pattern (required) - a beet.pattern object.
• onCallback (required) - a function to call on pattern's pulses e.g. 1's
• offCallback (optional) - a function to call on pattern's empty slots e.g. 0's.

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

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.

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);
}

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.

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

• audioparam (required) - an AudioParam object to be automated.
• now (required) - the time for the automation to start, e.g. the time parameter in beet callback.
• opts (optional) - an JavaScript object that contains the envelope parameters.
  • start (optional) - the start value for the automation curve. the audio param will be set to this value at the beginning of the automation.
  • peak (optional) - the maximum value for the automation curve that the attack stage will end up in.
  • attack (optional) - the time in seconds for the attack stage.
  • decay (optional) - the time in seconds for the decay stage.
  • sustain (optional) - the value for that the decay stage will end up in.
  • release (optional) - the time in seconds for the release stage.

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);

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

• path (required) - the path to your audio file.
• success (required) - function to be called on load success. The passed function will be called with a buffer parameters which is an AudioBuffer object.
• failure (required) - function to be called on load or decode error.

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

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

• midi_note (required) - the midi note number (0 to 127).

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

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

• note_name (required) - the note name followed by octave e.g. 'a4'

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

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

• midi_note (required) - the midi note number (0 to 127).

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