files/en-us/web/api/audiobuffer/getchanneldata/index.md
{{ APIRef("Web Audio API") }}
The getChannelData() method of the {{ domxref("AudioBuffer") }} Interface returns a {{jsxref("Float32Array")}} containing the PCM data associated with the channel, defined by the channel parameter (with 0 representing the first channel).
getChannelData(channel)
channel
channel index value is greater than of equal to {{domxref("AudioBuffer.numberOfChannels")}}, an INDEX_SIZE_ERR exception will be thrown.A {{jsxref("Float32Array")}}.
In the following example we create a two second buffer, fill it with white noise, and then play it via an {{ domxref("AudioBufferSourceNode") }}. The comments should clearly explain what is going on. You can also run the code live, or view the source.
const audioCtx = new AudioContext();
const button = document.querySelector("button");
const pre = document.querySelector("pre");
const myScript = document.querySelector("script");
pre.textContent = myScript.textContent;
// Stereo
const channels = 2;
// Create an empty two second stereo buffer at the
// sample rate of the AudioContext
const frameCount = audioCtx.sampleRate * 2.0;
const myArrayBuffer = audioCtx.createBuffer(2, frameCount, audioCtx.sampleRate);
button.onclick = () => {
// Fill the buffer with white noise;
// just random values between -1.0 and 1.0
for (let channel = 0; channel < channels; channel++) {
// This gives us the actual ArrayBuffer that contains the data
const nowBuffering = myArrayBuffer.getChannelData(channel);
for (let i = 0; i < frameCount; i++) {
// Math.random() is in [0; 1.0]
// audio needs to be in [-1.0; 1.0]
nowBuffering[i] = Math.random() * 2 - 1;
}
}
// Get an AudioBufferSourceNode.
// This is the AudioNode to use when we want to play an AudioBuffer
const source = audioCtx.createBufferSource();
// set the buffer in the AudioBufferSourceNode
source.buffer = myArrayBuffer;
// connect the AudioBufferSourceNode to the
// destination so we can hear the sound
source.connect(audioCtx.destination);
// start the source playing
source.start();
};
{{Specifications}}
{{Compat}}