moderate-exponentialRamp.html

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This WPT test may be referenced by the following Test IDs:
- /webaudio/the-audio-api/the-audioparam-interface/moderate-exponentialRamp.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<title>Test exponentialRampToValueAtTime() with a moderate ratio of change</title>

<script src="/resources/testharness.js"></script>

<script src="/resources/testharnessreport.js"></script>

<script>

'use strict';

promise_test(async function() {

  const bufferSize = 128;

  const sampleRate = 16384;

  // 3 * 2^6, not a power of two, so that there is some rounding error in the

  // exponent

  const rampEndSample = 192;

  // These values are chosen so that there is rounding error in

  // (offset1/offset0)^(1/rampEndSample).

  const offset0 = 4.;

  const offset1 = 7.;

  // 8 units in the last place (ulp) is a generous tolerance if single

  // precision powf() is used.  Math.pow(2, -23) ~ 1 ulp.

  // A simple recurrence relation formulation with only single precision

  // arithmetic applied across the whole rendering quantum would accumulate

  // error up to 50 ulp, losing 5.6 of the 24 bits of precision.

  const relativeTolerance = 8 * Math.pow(2, -23);

  const context = new OfflineAudioContext(1, bufferSize, sampleRate);

  const source = new ConstantSourceNode(context);

  source.start();

  // Explicit event to work around

  // https://bugzilla.mozilla.org/show_bug.cgi?id=1265393

  source.offset.setValueAtTime(offset0, 0.);

  source.offset.exponentialRampToValueAtTime(offset1, rampEndSample/sampleRate);

  source.connect(context.destination);

  const buffer = await context.startRendering();

  assert_equals(buffer.length, bufferSize, "output buffer length");

  const output = buffer.getChannelData(0);

  const ratio = offset1 / offset0;

  for (let i = 0; i < bufferSize; ++i) {

    // Math.pow() uses double precision, while `output` has single precision,

    // but `tolerance` is more than enough to accommodate differences.

    const expected = offset0 * Math.pow(offset1/offset0, i/rampEndSample);

    assert_approx_equals(

      output[i],

      expected,

      relativeTolerance * expected,

      "scheduled value at " + i);

});

</script>