sub-sample-buffer-stitching.html

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  <head>

    <title>

      Test Sub-Sample Accurate Stitching of ABSNs

    </title>

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

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

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

  </head>

  <body>

    <script>

      promise_test(async t => {

        // Sub‑sample stitching with identical context/buffer rates.

        const sampleRate = 44100;

        const bufferRate = 44100;

        const bufferLength = 30;

        // Experimentally determined thresholds. DO NOT relax these values

        // too far from these values to make the tests pass.

        const errorThreshold = 9.0957e-5;

        const snrThreshold = 85.580;

        assert_equals(sampleRate, 44100, 'Test 1: context.sampleRate');

        const resultBuffer =

            await testBufferStitching(sampleRate, bufferRate, bufferLength);

        const actual = resultBuffer.getChannelData(0);

        const expected = resultBuffer.getChannelData(1);

        assert_array_approximately_equals(

            actual,

            expected,

            errorThreshold,

            `Stitched sine‑wave buffers at sample rate ${bufferRate}`);

        const SNR = 10 * Math.log10(computeSNR(actual, expected));

        assert_greater_than_equal(

            SNR,

            snrThreshold,

            `SNR (${SNR.toFixed(3)} dB) should be ≥ ${snrThreshold} dB`);

      }, 'buffer-stitching-1');

      promise_test(async t => {

        // Sub‑sample stitching with differing context/buffer rates.

        const sampleRate = 44100;

        const bufferRate = 43800;

        const bufferLength = 30;

        // Experimentally determined thresholds. DO NOT relax these values

        // too far from these values to make the tests pass.

        const errorThreshold = 3.8986e-3;

        const snrThreshold = 65.737;

        assert_equals(sampleRate, 44100, 'Test 2: context.sampleRate');

        const resultBuffer = await testBufferStitching(

            sampleRate,

            bufferRate,

            bufferLength);

        const actual = resultBuffer.getChannelData(0);

        const expected = resultBuffer.getChannelData(1);

        assert_array_approximately_equals(

            actual,

            expected,

            errorThreshold,

            `Stitched sine‑wave buffers at sample rate ${bufferRate}`);

        const SNR = 10 * Math.log10(computeSNR(actual, expected));

        assert_greater_than_equal(

            SNR,

            snrThreshold,

            `SNR (${SNR.toFixed(3)} dB) should be ≥ ${snrThreshold} dB`);

      }, 'buffer-stitching-2');

      // Create graph to test stitching of consecutive ABSNs.  The context rate

      // is |sampleRate|, and the buffers have a fixed length of |bufferLength|

      // and rate of |bufferRate|.  The |bufferRate| should not be too different

      // from |sampleRate| because of interpolation of the buffer to the context

      // rate.

      function testBufferStitching(sampleRate, bufferRate, bufferLength) {

        // The OfflineAudioContext used for rendering.

        // Channel 0 captures the stitched output.

        // Channel 1 records the expected reference signal.

        const context = new OfflineAudioContext({

          numberOfChannels: 2,

          length: sampleRate,

          sampleRate: sampleRate,

});

        const merger = new ChannelMergerNode(

            context, {numberOfInputs: context.destination.channelCount});

        merger.connect(context.destination);

        // Reference signal (channel 1): pure 440 Hz sine wave

        const ref = new OscillatorNode(context, {frequency: 440, type: 'sine'});

        ref.connect(merger, 0, 1);

        ref.start();

        // The test signal is a bunch of short AudioBufferSources containing

        // bits of a sine wave.

        const waveSignal = new Float32Array(context.length);

        const omega = 2 * Math.PI / bufferRate * ref.frequency.value;

        for (let k = 0; k < context.length; ++k) {

          waveSignal[k] = Math.sin(omega * k);

        // Slice the sine wave into many little buffers to be assigned to ABSNs

        // that are started at the appropriate times to produce a final sine

        // wave.

        for (let k = 0; k < context.length; k += bufferLength) {

          const buffer =

              new AudioBuffer({length: bufferLength, sampleRate: bufferRate});

          // Copy the slice into the AudioBuffer’s first (and only) channel.

          buffer.copyToChannel(waveSignal.slice(k, k + bufferLength), 0);

          const src = new AudioBufferSourceNode(context, {buffer: buffer});

          src.connect(merger, 0, 0);

          src.start(k / bufferRate);

        return context.startRendering();

    </script>

  </body>

</html>