realtimeanalyser-fft-scaling.html

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This WPT test may be referenced by the following Test IDs:
- /webaudio/the-audio-api/the-analysernode-interface/realtimeanalyser-fft-scaling.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<html>

  <head>

    <title>

      realtimeanalyser-fft-scaling.html

    </title>

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

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

    <script src="/webaudio/resources/audit-util.js"></script>

    <script src="/webaudio/resources/audit.js"></script>

  </head>

  <body>

    <div id="description"></div>

    <div id="console"></div>

    <script id="layout-test-code">

      let audit = Audit.createTaskRunner();

      // The number of analysers. We have analysers from size for each of the

      // possible sizes of 2^5 to 2^15 for a total of 11.

      let numberOfAnalysers = 11;

      let sampleRate = 44100;

      let nyquistFrequency = sampleRate / 2;

      // Frequency of the sine wave test signal.  Should be high enough so that

      // we get at least one full cycle for the 32-point FFT.  This should also

      // be such that the frequency should be exactly in one of the FFT bins for

      // each of the possible FFT sizes.

      let oscFrequency = nyquistFrequency / 16;

      // The actual peak values from each analyser.  Useful for examining the

      // actual peak values.

      let peakValue = new Array(numberOfAnalysers);

      // For a 0dBFS sine wave, we would expect the FFT magnitude to be 0dB as

      // well, but the analyzer node applies a Blackman window (to smooth the

      // estimate).  This reduces the energy of the signal so the FFT peak is

      // less than 0dB.  The threshold value given here was determined

      // experimentally.

//

      // See https://code.google.com/p/chromium/issues/detail?id=341596.

      let peakThreshold = [

        -14.43, -13.56, -13.56, -13.56, -13.56, -13.56, -13.56, -13.56, -13.56,

        -13.56, -13.56

];

      function checkResult(order, analyser, should) {

        return function() {

          let index = order - 5;

          let fftSize = 1 << order;

          let fftData = new Float32Array(fftSize);

          analyser.getFloatFrequencyData(fftData);

          // Compute the frequency bin that should contain the peak.

          let expectedBin =

              analyser.frequencyBinCount * (oscFrequency / nyquistFrequency);

          // Find the actual bin by finding the bin containing the peak.

          let actualBin = 0;

          peakValue[index] = -1000;

          for (k = 0; k < analyser.frequencyBinCount; ++k) {

            if (fftData[k] > peakValue[index]) {

              actualBin = k;

              peakValue[index] = fftData[k];

          should(actualBin, (1 << order) + '-point FFT peak position')

              .beEqualTo(expectedBin);

          should(

              peakValue[index], (1 << order) + '-point FFT peak value in dBFS')

              .beGreaterThanOrEqualTo(peakThreshold[index]);

      audit.define(

            label: 'FFT scaling tests',

            description: 'Test Scaling of FFT in AnalyserNode'

},

          async function(task, should) {

            let tests = [];

            for (let k = 5; k <= 15; ++k)

              await runTest(k, should);

            task.done();

});

      function runTest(order, should) {

        let context = new OfflineAudioContext(1, 1 << order, sampleRate);

        // Use a sine wave oscillator as the reference source signal.

        let osc = context.createOscillator();

        osc.type = 'sine';

        osc.frequency.value = oscFrequency;

        osc.connect(context.destination);

        let analyser = context.createAnalyser();

        // No smoothing to simplify the analysis of the result.

        analyser.smoothingTimeConstant = 0;

        analyser.fftSize = 1 << order;

        osc.connect(analyser);

        osc.start();

        return context.startRendering().then(() => {

          checkResult(order, analyser, should)();

});

      audit.run();

    </script>

  </body>

</html>