alexanderwallin/emcc-audio-pointer-noise.c

## 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;
  }
}

## 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>

## 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()

## emcc-audio-pointer-noise.sh
emcc -o dsp.c.js -s EXPORTED_FUNCTIONS="['_add_noise']" -s ASSERTIONS=1 dsp.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;
	}
	}
	<!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>
	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()