Javascript: UInt8Array to Float32Array

Question

I have some audio buffer in usigned 8bit PCM format need to play via web audio which only accept signed 32bit PCM. And now I have ArrayBuffer for pieces of pcm_u8 data(come from Uint8array). How can I convert it to Float32Array?

Answer 1

This function converts an ArrayBuffer to Float32Array

var convertBlock(buffer) { // incoming data is an ArrayBuffer
    var incomingData = new Uint8Array(buffer); // create a uint8 view on the ArrayBuffer
    var i, l = incomingData.length; // length, we need this for the loop
    var outputData = new Float32Array(incomingData.length); // create the Float32Array for output
    for (i = 0; i < l; i++) {
        outputData[i] = (incomingData[i] - 128) / 128.0; // convert audio to float
    }
    return outputData; // return the Float32Array
}

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This one converts a Uint8Array to Float32Array

var convertBlock(incomingData) { // incoming data is a UInt8Array
    var i, l = incomingData.length;
    var outputData = new Float32Array(incomingData.length);
    for (i = 0; i < l; i++) {
        outputData[i] = (incomingData[i] - 128) / 128.0;
    }
    return outputData;
}

Answer 2

ECMAScript 2015 and onwards has TypedArray.from which converts any typed array (and indeed, any iterable) to the specified typed array format.

So converting a Uint8Array to a Float32Array is now as easy as:

const intArray = new Uint8Array()
const floatArray = Float32Array.from(intArray)