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alexanderwallin/emcc-audio-pointer-noise.c

Last active January 6, 2017 15:27
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Emscripten audio noise using pointers
Raw
emcc-audio-pointer-noise.c
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
float get_random_float(const float min, const float max) {
return min + (max - min) * ((float) rand() / (float) RAND_MAX);
}
void add_noise(const void *inBuffer, unsigned int inBufferLength, const void *outBuffer) {
int i = 0;
float* inData = (float*) inBuffer;
float* outData = (float*) outBuffer;
printf("in test method: size of inBuffer buffer = %d\n", inBufferLength);
for (i = 0; i < inBufferLength; i++) {
float noise = get_random_float(-0.1f, 0.1f);
outData[i] = inData[i] + noise;
}
}
Raw
emcc-audio-pointer-noise.html
<!DOCTYPE html>
<html>
<head>
<title>emcc-audio-add-noise</title>
</head>
<body>
<script src="dsp.c.js"></script>
<script src="app.js"></script>
</body>
</html>
Raw
emcc-audio-pointer-noise.js
const addNoise = Module.cwrap('add_noise', 'number', ['number', 'number'])
const ctx = new AudioContext()
const osc = ctx.createOscillator()
osc.frequency.value = 440
const noise = ctx.createScriptProcessor(512, 2, 2)
noise.onaudioprocess = (evt) => {
// const timeStart = Date.now()
const { inputBuffer, outputBuffer } = evt
for (let c = 0; c < outputBuffer.numberOfChannels; c++) {
const channelInput = inputBuffer.getChannelData(c)
const channelOutput = outputBuffer.getChannelData(c)
const numSamples = channelInput.length
const inPtr = Module._malloc(numSamples * Float32Array.BYTES_PER_ELEMENT)
const inBuf = new Float32Array(Module.HEAPF32.buffer, inPtr, numSamples)
const outPtr = Module._malloc(numSamples * Float32Array.BYTES_PER_ELEMENT)
const outBuf = new Float32Array(Module.HEAPF32.buffer, outPtr, numSamples)
for (let is = 0; is < channelInput.length; is++) {
inBuf[is] = channelInput[is]
}
addNoise(inPtr, inBuf.length, outPtr)
for (let os = 0; os < channelOutput.length; os++) {
channelOutput[os] = outBuf[os]
}
Module._free(inPtr)
Module._free(outPtr)
}
// console.log(Date.now() - timeStart)
}
const vol = ctx.createGain()
vol.gain.value = 0.1
osc.connect(noise)
noise.connect(vol)
vol.connect(ctx.destination)
osc.start()
Raw
emcc-audio-pointer-noise.sh
emcc -o dsp.c.js -s EXPORTED_FUNCTIONS="['_add_noise']" -s ASSERTIONS=1 dsp.c
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