Web Audio

Audio Node Types

Source Nodes - audio buffers, live inputs, <audio> tag, ocillators, JS Processors.
Modification Nodes - Filters, Convolvers, Panners, JS Processors.
Analysis Nodes - Analyzers, JS Processors.
Destination Nodes - Audio outputs and offline processing buffers.

Create Context

    var contextClass = (window.AudioContext ||
    window.webkitAudioContext ||
    window.mozAudioContext ||
    window.oAudioContext ||
    window.msAudioContext);

    if (contextClass) {
    // Web Audio API is available.var context = new contextClass();
} else {
    // Web Audio API is not available. Ask the user to use a supported browser.
}

Connect Context

// Create the source.
var source = context.createBufferSource();

// Create the gain node.
var gain = context.createGain();

// Connect source to filter, filter to destination.
source.connect(gain);
gain.connect(context.destination);

// Disconnect
source.disconnect(0);
gain.disconnect(0);
source.connect(context.destination);

Modular Routing

Sound Waves
Digital Sound
Sample Rate
Bit Depth
Bit Rate
Quantization
PCM - Pulse code modulation. AudioBuffer is an array of PCM data.
Audio Encoding Formats - FLAC(lossless) guaranteed bit to bit restore, MP3(lossy)

Loading and Playing Sounds

    var request = new XMLHttpRequest();
    request.open('GET', url, true);
    request.responseType = 'arraybuffer';

    // Decode asynchronously
    request.onload = function() {
    context.decodeAudioData(request.response, function(theBuffer) {
        buffer = theBuffer;
    }, onError);
}

    request.send();

    function playSound(buffer) {
    var source = context.createBufferSource();
    source.buffer = buffer;
    source.connect(context.destination);
    source.start(0);
}

Timing Model

Not used in web audio.

setTimeout()
setInterval()
new Date()
window.performance.now()

Used

AudioContext.currentTime

Playback of web audio is in float seconds not integer milliseconds.

Simple Sequencer

This sequencer adds all notes at the start and does not use a time window for dynamic sequencing. Once the events are sequenced natively, you cannot remove them.

for (var bar = 0; bar < 2; bar++) {
    var time = startTime + bar * 8 * eighthNoteTime;
    // Play the bass (kick) drum on beats 1, 5
    playSound(kick, time);
    playSound(kick, time + 4 * eighthNoteTime);
    // Play the snare drum on beats 3, 7
    playSound(snare, time + 2 * eighthNoteTime);
    playSound(snare, time + 6 * eighthNoteTime);
    // Play the hihat every eighth note.
    for (var i = 0; i < 8; ++i) {
        playSound(hihat, time + i * eighthNoteTime);
    }
}

Changing Audio Parameters

setValueAtTime()
setValueCurveAtTime()

    // Create a gain node.
    var gainNode = context.createGain();

    // Connect the source to the gain node.
    source.connect(gainNode);

    // Connect the gain node to the destination.
    gainNode.connect(context.destination);

    // Reduce the volume.
    gainNode.gain.value = 0.5;
    // OR
    gainNode.gain.setValueAtTime(0.5, context.currentTime + 1);