audiobuffersource-testing.js

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function createTestBuffer(context, sampleFrameLength) {

  let audioBuffer =

      context.createBuffer(1, sampleFrameLength, context.sampleRate);

  let channelData = audioBuffer.getChannelData(0);

  // Create a simple linear ramp starting at zero, with each value in the buffer

  // equal to its index position.

  for (let i = 0; i < sampleFrameLength; ++i)

    channelData[i] = i;

  return audioBuffer;

function checkSingleTest(renderedBuffer, i, should) {

  let renderedData = renderedBuffer.getChannelData(0);

  let offsetFrame = i * testSpacingFrames;

  let test = tests[i];

  let expected = test.expected;

  let description;

  if (test.description) {

    description = test.description;

  } else {

    // No description given, so create a basic one from the given test

    // parameters.

    description =

        'loop from ' + test.loopStartFrame + ' -> ' + test.loopEndFrame;

    if (test.offsetFrame)

      description += ' with offset ' + test.offsetFrame;

    if (test.playbackRate && test.playbackRate != 1)

      description += ' with playbackRate of ' + test.playbackRate;

  let framesToTest;

  if (test.renderFrames)

    framesToTest = test.renderFrames;

  else if (test.durationFrames)

    framesToTest = test.durationFrames;

  // Verify that the output matches

  let prefix = 'Case ' + i + ': ';

  should(

      renderedData.slice(offsetFrame, offsetFrame + framesToTest),

      prefix + description)

      .beEqualToArray(expected);

  // Verify that we get all zeroes after the buffer (or duration) has passed.

  should(

      renderedData.slice(

          offsetFrame + framesToTest, offsetFrame + testSpacingFrames),

      prefix + description + ': tail')

      .beConstantValueOf(0);

function checkAllTests(renderedBuffer, should) {

  for (let i = 0; i < tests.length; ++i)

    checkSingleTest(renderedBuffer, i, should);

// Create the actual result by modulating playbackRate or detune AudioParam of

// ABSN. |modTarget| is a string of AudioParam name, |modOffset| is the offset

// (anchor) point of modulation, and |modRange| is the range of modulation.

//

//   createSawtoothWithModulation(context, 'detune', 440, 1200);

//

// The above will perform a modulation on detune within the range of

// [1200, -1200] around the sawtooth waveform on 440Hz.

function createSawtoothWithModulation(context, modTarget, modOffset, modRange) {

  let lfo = context.createOscillator();

  let amp = context.createGain();

  // Create a sawtooth generator with the signal range of [0, 1].

  let phasor = context.createBufferSource();

  let phasorBuffer = context.createBuffer(1, sampleRate, sampleRate);

  let phasorArray = phasorBuffer.getChannelData(0);

  let phase = 0, phaseStep = 1 / sampleRate;

  for (let i = 0; i < phasorArray.length; i++) {

    phasorArray[i] = phase % 1.0;

    phase += phaseStep;

  phasor.buffer = phasorBuffer;

  phasor.loop = true;

  // 1Hz for audible (human-perceivable) parameter modulation by LFO.

  lfo.frequency.value = 1.0;

  amp.gain.value = modRange;

  phasor.playbackRate.value = modOffset;

  // The oscillator output should be amplified accordingly to drive the

  // modulation within the desired range.

  lfo.connect(amp);

  amp.connect(phasor[modTarget]);

  phasor.connect(context.destination);

  lfo.start();

  phasor.start();