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zero-crossings.html
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<!--
Copyright 2012, Google Inc.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following disclaimer
in the documentation and/or other materials provided with the
distribution.
* Neither the name of Google Inc. nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>
Title
</title>
<link rel="stylesheet" type="text/css" href = "style/simple.css" />
<!-- Slider stuff -->
<script type="text/javascript" src="lib/buffer-loader.js"></script>
<script type="text/javascript" src="lib/events.js"></script>
<style type="text/css">
#slider { margin: 10px; }
</style>
<!-- Our javascript code -->
<script type="text/javascript">
// Events
// init() once the page has finished loading.
window.onload = init;
var assetList =
[
{"url": "sounds/drum-samples/loops/break29.wav", "loopStartFrame": 70000, "loopEndFrame": 37996},
// {"url": "sounds/drum-samples/loops/blueyellow.wav", "loopStartFrame": 70000, "loopEndFrame": 37996},
// {"url": "sounds/hyper-reality/guitar-chords.wav", "loopStartFrame": 70000, "loopEndFrame": 37996},
// {"url": "sounds/hyper-reality/human-voice.wav", "loopStartFrame": 70000, "loopEndFrame": 37996},
];
// a list of AudioBuffers for the assets.
var bufferList;
var buffer;
var currentIndex = 0;
var canvas;
var canvasContext;
var backgroundColor = "rgb(0, 0, 0)";
var curveColor = "rgb(192,192,192)";
var gridColor = "rgb(200,200,200)";
var gridColor2 = "rgb(255,50,50)";
var white = "rgb(255,255,255)";
var context;
var drawSampleOffset = 80000;
var crossings = new Float32Array(16384);
function findZeroCrossings() {
var n = buffer.length;
var j = 0;
// Assume stereo.
var pL = buffer.getChannelData(0);
var pR = buffer.getChannelData(1);
var last = 0;
var lastIndex = 0;
var negPeak = 0;
var posPeak = 0;
var aveNegPeak = 0;
var avePosPeak = 0;
var crossingIndex = 0;
for (var i = 0; i < n; ++i) {
var sample = 0.5 * (pL[i] + pR[i]);
if (last < 0 && sample > 0) {
// Positive crossing.
if (negPeak < 0.5 * aveNegPeak) {
crossingIndex = i;
negPeak = 0;
}
} else if (last > 0 && sample < 0) {
// Negative crossing.
var delta = j==0 ? 10000 : crossingIndex - crossings[j - 1];
if (posPeak > 0.5 * avePosPeak && crossingIndex != -1 && delta > 128) {
crossings[j] = crossingIndex;
// if (j < 1000)
// console.log("i: " + i + " deltaIndex: " + deltaIndex);
// var deltaIndex = i - lastIndex;
// lastIndex = i;
j++;
posPeak = 0;
}
}
if (sample > posPeak)
posPeak = sample;
if (sample < negPeak)
negPeak = sample;
if (sample > avePosPeak)
avePosPeak = sample;
if (sample < aveNegPeak)
aveNegPeak = sample;
// Decay
avePosPeak *= 0.999;
aveNegPeak *= 0.999;
last = sample;
if (j >= crossings.length)
break;
}
console.log("Final j: " + j);
}
function drawCurve() {
var info = document.getElementById("info");
var width = canvas.width;
var height = canvas.height;
var pL = buffer.getChannelData(0);
var pR = buffer.getChannelData(1);
var curveLength = buffer.length;
var drawSampleLength = width /*1000*/;
var scale = drawSampleLength / width;
canvasContext.fillStyle = backgroundColor;
canvasContext.fillRect(0, 0, width, height);
canvasContext.lineWidth = 1;
// Draw PCM data.
canvasContext.beginPath();
canvasContext.strokeStyle = gridColor2;
var pcmValue = 0.5 * (pL[drawSampleOffset] + pR[drawSampleOffset]);
var y0 = 0.5*height - height * 0.5*pcmValue;
var halfWidth = 0.5*width;
canvasContext.moveTo(0, y0);
for (var i = 0; i <= width; ++i) {
// var index = Math.floor(i * scale + drawSampleOffset);
var index = i + drawSampleOffset;
var pcmValue = 0.5 * (pL[index] + pR[index]);
var y = 0.5*height - height * 0.5*pcmValue;
canvasContext.lineTo(i, y);
}
canvasContext.stroke();
// Draw 0 crossings.
var j = 0;
// Find first crossing
var k = Math.floor(drawSampleOffset);
while (k > crossings[j])
j++;
// if (j > 0) j++;
canvasContext.beginPath();
canvasContext.strokeStyle = white;
for (var i = 0; i <= width; ++i) {
// var index = Math.floor(i * scale + drawSampleOffset);
var index = i + drawSampleOffset;
if (index == crossings[j]) {
j++;
while (crossings[j] <= index && j < crossings.length)
j++;
canvasContext.moveTo(i, 0);
canvasContext.lineTo(i, height);
}
}
canvasContext.stroke();
// Draw 0 line.
canvasContext.beginPath();
canvasContext.strokeStyle = white;
canvasContext.moveTo(0, 0.5*height);
canvasContext.lineTo(width, 0.5*height);
canvasContext.stroke();
}
function handleKeyDown(event) {
var code = event.keyCode;
var delta = 200;
if (code == 37) {
if (drawSampleOffset > delta)
drawSampleOffset -= delta;
} else if (code == 39) {
if (drawSampleOffset < buffer.length - delta)
drawSampleOffset += delta;
}
drawCurve();
}
function updateCurrentBuffer(index) {
currentIndex = index;
buffer = bufferList[currentIndex];
findZeroCrossings();
var info = document.getElementById('info');
var asset = assetList[currentIndex];
var s = asset.url + ": " + buffer.length;
info.innerHTML = s;
drawCurve();
}
function loadAssets(url) {
// Load asynchronously
var urlList = new Array();
for (var i = 0; i < assetList.length; ++i) {
var url = assetList[i].url;
urlList.push(url);
}
console.log(urlList);
bufferLoader = new BufferLoader(context, urlList, finishedLoading);
bufferLoader.load();
}
function finishedLoading(bl) {
bufferList = bl; // Keep track of the loaded buffers.
document.addEventListener("keydown", handleKeyDown, true);
updateCurrentBuffer(0);
}
function init() {
canvas = document.getElementById('canvasID');
canvasContext = canvas.getContext('2d');
context = new AudioContext();
loadAssets();
}
</script>
</head>
<body>
<!-- Sliders and other controls will be added here -->
<div id="controls"> </div>
<canvas id="canvasID" width="2048" height="768" style="border: 2px inset blue;">
</canvas>
<div id="info"> </div>
</body>
</html>