Testing WebAudioAPI Delay precision

delaytest.js

"use strict";

var AudioContext = webkitAudioContext || AudioContext;
var context = new AudioContext();
var length = 44100;

// 2 Buffers to hold samples
var bufferSourceNode = context.createBufferSource();
var counterNode = context.createBufferSource();

// Scope to see what's going through
var scopeNode = context.createScriptProcessor();

var delayNode = context.createDelay();

// Delay by a single sample
delayNode.delayTime.value = 1.0/44100;

// Create counter buffers - monotonically increasing values
counterNode.buffer = createCounterBuffer( length );
bufferSourceNode.buffer = createCounterBuffer( length );

// Scope callback
scopeNode.onaudioprocess = printPosition;

// Hook up one buffer through delay
bufferSourceNode.connect(delayNode);
delayNode.connect(scopeNode);
counterNode.connect( scopeNode );
scopeNode.connect(context.destination);

//Start
counterNode.start(0);
bufferSourceNode.start(0);


// Prints the first sample of each frame.
// Each sample is the sum of the two counter buffers
// So the value of the sample will indicate where the buffer
// is being played from.
function printPosition( processEvent ) {
    var inputBuffer = processEvent.inputBuffer.getChannelData( 0 );
    console.log(inputBuffer[  0 ]);
}

// Create motonically increasing, 1,2,3,4...
// buffer to be used to figure out the
// current playing position of a delayed buffer.
function createCounterBuffer( length ) {
    var array = new Float32Array( length );
    var audioBuf = context.createBuffer( 1, length, 44100 );

    for ( var index = 0; index < length; index++ ) {
        array[ index ] = index;
    }

    audioBuf.getChannelData( 0 )
    .set( array );

    var inputBuffer = audioBuf.getChannelData( 0 );
    //console.log("S " + inputBuffer[  inputBuffer.length -1 ]);

    return audioBuf;
}