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<script type="text/javascript">
</script>
<table>
<tr>
<th>
Not normalized
</th>
<th>
Normalized
</th>
<th>
Computed gain
</th>
</tr>
<tr>
<td>
<audio controls> <source src="sample-a.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<audio id="sample-a-n" controls> <source src="sample-a.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<div id="sample-a-d"></div>
</td>
</tr>
<tr>
<td>
<audio controls> <source src="sample-b.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<audio id="sample-b-n" controls> <source src="sample-b.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<div id="sample-b-d"></div>
</td>
</tr>
<tr>
<td>
<audio controls> <source src="sample-c.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<audio id="sample-c-n" controls> <source src="sample-c.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<div id="sample-c-d"></div>
</td>
</tr>
<tr>
<td>
<audio controls> <source src="sample-d.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<audio id="sample-d-n" controls> <source src="sample-d.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<div id="sample-d-d"></div>
</td>
</tr>
<tr>
<td>
<audio controls> <source src="sample-e.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<audio id="sample-e-n" controls> <source src="sample-e.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<div id="sample-e-d"></div>
</td>
</tr>
<tr>
<td>
<audio controls> <source src="sample-f.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<audio id="sample-f-n" controls> <source src="sample-f.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<div id="sample-f-d"></div>
</td>
</tr>
<tr>
<td>
<audio controls> <source src="sample-g.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<audio id="sample-g-n" controls> <source src="sample-g.mp3" type="audio/mpeg">Audio element not supported</audio>
</td>
<td>
<div id="sample-g-d"></div>
</td>
</tr>
</table>
<script type="text/javascript">
function start() {
var audioCtx = new AudioContext();
// http://wiki.hydrogenaud.io/index.php?title=ReplayGain_specification
// TODO: do the loudness filtering (Butterworth, Yulewalk) IIR filters
function normalizedAudioElement(name) {
var audioElem = document.getElementById(name + "-n");
var src = audioCtx.createMediaElementSource(audioElem);
var gainNode = audioCtx.createGain();
gainNode.gain.value = 1.0;
audioElem.addEventListener("play", function() {
src.connect(gainNode);
gainNode.connect(audioCtx.destination);
}, true);
audioElem.addEventListener("pause", function() {
// disconnect the nodes on pause, otherwise all nodes always run
src.disconnect(gainNode);
gainNode.disconnect(audioCtx.destination);
}, true);
fetch(name + ".mp3")
.then(function(res) { return res.arrayBuffer(); })
.then(function(buf) {
return audioCtx.decodeAudioData(buf);
}).then(function(decodedData) {
var decodedBuffer = decodedData.getChannelData(0);
var sliceLen = Math.floor(decodedData.sampleRate * 0.05);
var averages = [];
var sum = 0.0;
for (var i = 0; i < decodedBuffer.length; i++) {
sum += decodedBuffer[i] ** 2;
if (i % sliceLen === 0) {
sum = Math.sqrt(sum / sliceLen);
averages.push(sum);
sum = 0;
}
}
// Ascending sort of the averages array
averages.sort(function(a, b) { return a - b; });
// Take the average at the 95th percentile
var a = averages[Math.floor(averages.length * 0.95)];
var gain = 1.0 / a;
// Perform some clamping
// gain = Math.max(gain, 0.02);
// gain = Math.min(gain, 100.0);
// ReplayGain uses pink noise for this one one but we just take
// some arbitrary value... we're no standard
// Important is only that we don't output on levels
// too different from other websites
gain = gain / 10.0;
console.log("gain determined", name, a, gain);
gainNode.gain.value = gain;
var gainTextElem = document.getElementById(name + "-d");
gainTextElem.textContent = gain.toPrecision(4);
});
}
normalizedAudioElement("sample-a");
normalizedAudioElement("sample-b");
normalizedAudioElement("sample-c");
normalizedAudioElement("sample-d");
normalizedAudioElement("sample-e");
normalizedAudioElement("sample-f");
normalizedAudioElement("sample-g");
}
</script>
|
