Tone Playing Experiment with HTML5’s Web Audio API

tl;dr: Tone Player (works in Google Chrome and Safari 6+ only)

One of my favorite parts of the QBasic class I had in high school was discovering how to play sounds. It introduced a whole new layer on which to experiment with.

Until recently, adding custom sounds to a web application has not been a simple task. Thankfully, the W3C is working on a new high level audio specification called the Web Audio API that allows you to easily create and play sounds. Webkit based browsers have pushed out an implementation of this spec (Chrome and Safari 6+), and hopefully other browsers will follow suit soon. Previously, Mozilla had been working on a more lower level audio API called the Audio Data API, but it is now deprecated.

After seeing a few fancy demos of the Web Audio API, I decided to do some digging to see what all it could do. Sadly, there aren’t a lot of great up-to-date tutorials on how to use it. A couple of exceptions I found to this were the getting started tutorial at and a hand full of nice blog posts by Stuart Memo. However, I was also surprised to find that the Web Audio WC3 specification is actually very readable.

So with this fancy new API, how hard is it to create and play a simple tone? It’s pretty easy actually. The below code gives one example.

var context = new webkitAudioContext(),//webkit browsers only
    oscillator = context.createOscillator();

oscillator.type = 0; // sine wave
oscillator.frequency.value = 2000;
oscillator.noteOn && oscillator.noteOn(0);

You can also play more than one frequency at once. However, I found that playing too many tones together can crash the browser, so this is something you have to be careful about, and there may be a better way to do this.

var context = new webkitAudioContext(),
    oscillators = [], num = 5, ii;

for (ii = 0; ii < num; ii++) {
    oscillators[ii] = context.createOscillator();
    oscillators[ii].type = 0;
    oscillators[ii].frequency.value = 2000 + ii * 200;

var connectIt = function(ii) {
    oscillators[ii].noteOn && oscillators[ii].noteOn(0);
    if (ii < num) {
        setTimeout(function() {connectIt(ii);}, 1000);
    } else {
        setTimeout(function() {
            for (var jj = 0; jj < num; jj++) {
        }, 1000);


Oh, and you'll notice I check for the noteOn property before trying to use it. The spec says you need to use it, while Chrome tells me it doesn't exist. This appears to be a possible bug in Chrome's implementation.

With the basics down, I decided to create a simple Tone Player. It doesn't add much to what I've already showed you, but it has a few extra features. And in all honestly, it was actually made more to serve as a hearing test for myself. A couple years ago I had a hearing test done which indicated I had hearing issues, especially in my left ear. Since then I've been trying to take care of my hearing as best as possible. This tone generator is fascinating for me because I actually found that I can't hear certain frequencies (near 12000Hz), unless I really jack up the volume, but I can hear others fine all the way up to the 20k's. Hrm, probably time to schedule another appointment.

Anyway, enough about my hearing issues. Even though the API currently only works in a couple of browsers, it's a lot of fun, and I've hardly even dared to scratch the surface with this entry. I recommend checking it out if you have a few moments. If you're looking for a less experimental, more cross-browser way to play sound, I'd recommend checking out one of the many JavaScript libraries that have popped up to play audio. I'll link a few below for those who are interested.

8 thoughts on “Tone Playing Experiment with HTML5’s Web Audio API”

  1. Thanks. I was looking for webaudiokit tutorials and I found your site. I enjoyed playing around with the Tone Player. I can hear all the way to 15k, but I can’t hear anything above it.

  2. Hey so I’m working on a similar application – I’m having trouble figuring out how to make it dynamically change with the slider. I figured out how the change the volume via gain nodes with the addEventListener, but I’m stuck on how I should change the pitch of the sound dynamically.


  3. You can actually hear up to 20 kHz ? My ears died at around 9k or so …. damn that’s still on the pretty far left of the entire bar 🙁

    Anyway, excellent tutor and tone player you got here. I’ve been looking for something like this. We can actually make the browser sing with this. Very cool.

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