Arpeggiator

A Basic Arpeggiator

In this example, we'll create an arpeggiator which plays the next note in a series on every beat.

The Synthesizer

Tone.js has a number of instrument, each with nearly the same interface for triggering attacks and releases. Here we'll use Tone.MonoSynth, but you can easily swap the MonoSynth for a DuoSynth, FMSynth, or AMSynth without changing any of the rest of the code.

var synth = new Tone.MonoSynth();

We'll also connect our synth to the master output so that we can hear it.

synth.toMaster();

Triggering Notes

We can trigger the synth to start the attack portion of the note using triggerAttack -- this method takes a note and a time as arguments. To start the release portion of the note, call triggerRelease. Check out this Wikipedia article for more information about synthesizer envelopes.

For example, let's trigger the note "C4" then trigger the release a quarter second later (all values are in seconds):

synth.triggerAttack("C4", time);
synth.triggerRelease(time + 0.25);

These two methods are combined into a single call to triggerAttackRelease which takes the note as the first argument, the duration as the second, and the start time as the third argument.

synth.triggerAttackRelease("C4", 0.25, time);

The Arpeggio

Next let's pick a set of notes to arpeggiate over, like a C pentatonic scale. Then we'll set an interval and get the next note from the array on every loop.

var notes = ["C4", "E4", "G4", "A4"];
var position = 0;

setInterval(function(){
	var note = notes[position++];
	position = position % notes.length;
	synth.triggerAttackRelease(note, 0.25, time);
}, 500);

Timing the Notes

One way to make the arpeggiator loop is with setInterval as shown above. The problem is that the timing would be kinda loose since native Javascript timing is not very accurate or reliable. Instead we'll use Tone.Transport.setInterval which is defined in Tone.Transport. Tone's setInterval method looks very similar to Javascript's setInterval, except that Tone's method passes in the exact time when the event was scheduled to occur (and also takes its interval time in seconds instead of milliseconds). We'll use that time argument to schedule our synth's triggerAttackRelease function.

Tone.Transport.setInterval(function(time){
	...
	synth.triggerAttackRelease(note, 0.25, time);
}, 0.5);

The transport won't start firing events until it's started.

Tone.Transport.start();

Putting It Together

Here's what it looks like all together:

var notes = ["C4", "E4", "G4", "A4"];
var position = 0;

var synth = new Tone.MonoSynth();
synth.toMaster();

Tone.Transport.setInterval(function(time){
	var note = notes[position++];
	position = position % notes.length;
	synth.triggerAttackRelease(note, 0.25, time);
}, 0.5);

//the transport won't start firing events until it's started
Tone.Transport.start();

In the next example, we'll add some effects to our synthesizer.