iirfilter-getFrequencyResponse.html

<!DOCTYPE html>
<html>
  <head>
    <title>
      Test IIRFilter getFrequencyResponse() functionality
    </title>
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <script src="../../resources/audit-util.js"></script>
    <script src="../../resources/audit.js"></script>
    <script src="../../resources/biquad-filters.js"></script>
  </head>
  <body>
    <script id="layout-test-code">
      let sampleRate = 48000;
      // Some short duration; we're not actually looking at the rendered output.
      let testDurationSec = 0.01;

      // Number of frequency samples to take.
      let numberOfFrequencies = 1000;

      let audit = Audit.createTaskRunner();


      // Compute a set of linearly spaced frequencies.
      function createFrequencies(nFrequencies, sampleRate) {
        let frequencies = new Float32Array(nFrequencies);
        let nyquist = sampleRate / 2;
        let freqDelta = nyquist / nFrequencies;

        for (let k = 0; k < nFrequencies; ++k) {
          frequencies[k] = k * freqDelta;
        }

        return frequencies;
      }

      audit.define('1-pole IIR', (task, should) => {
        let context = new OfflineAudioContext(
            1, testDurationSec * sampleRate, sampleRate);

        let iir = context.createIIRFilter([1], [1, -0.9]);
        let frequencies =
            createFrequencies(numberOfFrequencies, context.sampleRate);

        let iirMag = new Float32Array(numberOfFrequencies);
        let iirPhase = new Float32Array(numberOfFrequencies);
        let trueMag = new Float32Array(numberOfFrequencies);
        let truePhase = new Float32Array(numberOfFrequencies);

        // The IIR filter is
        //   H(z) = 1/(1 - 0.9*z^(-1)).
        //
        // The frequency response is
        //   H(exp(j*w)) = 1/(1 - 0.9*exp(-j*w)).
        //
        // Thus, the magnitude is
        //   |H(exp(j*w))| = 1/sqrt(1.81-1.8*cos(w)).
        //
        // The phase is
        //   arg(H(exp(j*w)) = atan(0.9*sin(w)/(.9*cos(w)-1))

        let frequencyScale = Math.PI / (sampleRate / 2);

        for (let k = 0; k < frequencies.length; ++k) {
          let omega = frequencyScale * frequencies[k];
          trueMag[k] = 1 / Math.sqrt(1.81 - 1.8 * Math.cos(omega));
          truePhase[k] =
              Math.atan(0.9 * Math.sin(omega) / (0.9 * Math.cos(omega) - 1));
        }

        iir.getFrequencyResponse(frequencies, iirMag, iirPhase);

        // Thresholds were experimentally determined.
        should(iirMag, '1-pole IIR Magnitude Response')
            .beCloseToArray(trueMag, {absoluteThreshold: 2.8611e-6});
        should(iirPhase, '1-pole IIR Phase Response')
            .beCloseToArray(truePhase, {absoluteThreshold: 1.7882e-7});

        task.done();
      });

      audit.define('compare IIR and biquad', (task, should) => {
        // Create an IIR filter equivalent to the biquad filter. Compute the
        // frequency response for both and verify that they are the same.
        let context = new OfflineAudioContext(
            1, testDurationSec * sampleRate, sampleRate);

        let biquad = context.createBiquadFilter();
        let coef = createFilter(
            biquad.type, biquad.frequency.value / (context.sampleRate / 2),
            biquad.Q.value, biquad.gain.value);

        let iir = context.createIIRFilter(
            [coef.b0, coef.b1, coef.b2], [1, coef.a1, coef.a2]);

        let frequencies =
            createFrequencies(numberOfFrequencies, context.sampleRate);
        let biquadMag = new Float32Array(numberOfFrequencies);
        let biquadPhase = new Float32Array(numberOfFrequencies);
        let iirMag = new Float32Array(numberOfFrequencies);
        let iirPhase = new Float32Array(numberOfFrequencies);

        biquad.getFrequencyResponse(frequencies, biquadMag, biquadPhase);
        iir.getFrequencyResponse(frequencies, iirMag, iirPhase);

        // Thresholds were experimentally determined.
        should(iirMag, 'IIR Magnitude Response').beCloseToArray(biquadMag, {
          absoluteThreshold: 2.7419e-5
        });
        should(iirPhase, 'IIR Phase Response').beCloseToArray(biquadPhase, {
          absoluteThreshold: 2.7657e-5
        });

        task.done();
      });

      audit.define(
          {
            label: 'getFrequencyResponse',
            description: 'Test out-of-bounds frequency values'
          },
          (task, should) => {
            let context = new OfflineAudioContext(1, 1, sampleRate);
            let filter = new IIRFilterNode(
                context, {feedforward: [1], feedback: [1, -.9]});

            // Frequencies to test.  These are all outside the valid range of
            // frequencies of 0 to Nyquist.
            let freq = new Float32Array(2);
            freq[0] = -1;
            freq[1] = context.sampleRate / 2 + 1;

            let mag = new Float32Array(freq.length);
            let phase = new Float32Array(freq.length);

            filter.getFrequencyResponse(freq, mag, phase);

            // Verify that the returned magnitude and phase entries are alL NaN
            // since the frequencies are outside the valid range
            for (let k = 0; k < mag.length; ++k) {
              should(mag[k],
                  'Magnitude response at frequency ' + freq[k])
                  .beNaN();
            }

            for (let k = 0; k < phase.length; ++k) {
              should(phase[k],
                  'Phase response at frequency ' + freq[k])
                  .beNaN();
            }

            task.done();
          });

      audit.run();
    </script>
  </body>
</html>
chromium/third_party/blink/web_tests/external/wpt/webaudio/the-audio-api/the-iirfilternode-interface/iirfilter-getFrequencyResponse.html
