audioparam-connect-audioratesignal.html

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

<!DOCTYPE html>

<!--

Tests that an audio-rate signal (AudioNode output) can be connected to an

AudioParam.  Specifically, this tests that an audio-rate signal coming from an

AudioBufferSourceNode playing an AudioBuffer containing a specific curve can be

connected to an AudioGainNode's .gain attribute (an AudioParam).  Another

AudioBufferSourceNode will be the audio source having its gain changed.  We load

this one with an AudioBuffer containing a constant value of 1.  Thus it's easy

to check that the resultant signal should be equal to the gain-scaling curve.

-->

<html>

  <head>

    <title>

      audioparam-connect-audioratesignal.html

    </title>

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

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

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

  </head>

  <body>

    <script>

      const sampleRate = 44100.0;

      const lengthInSeconds = 1;

      let context;

      let constantOneBuffer;

      let linearRampBuffer;

      function checkResult(renderedBuffer) {

        const renderedData = renderedBuffer.getChannelData(0);

        const expectedData = linearRampBuffer.getChannelData(0);

        const n = renderedBuffer.length;

        assert_equals(

n,

            linearRampBuffer.length,

            'Rendered signal length should match control buffer length');

        // Check that the rendered result exactly matches the buffer used to

        // control gain.  This is because we're changing the gain of a signal

        // having constant value 1.

        let success = true;

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

          if (renderedData[i] != expectedData[i]) {

            success = false;

            break;

        assert_true(

            success,

            `Rendered signal exactly matches ` +

                `the audio-rate gain changing signal`);

      promise_test(async t => {

        const sampleFrameLength = sampleRate * lengthInSeconds;

        // Create offline audio context.

        context = new OfflineAudioContext(1, sampleFrameLength, sampleRate);

        // Create buffer used by the source which will have its gain controlled.

        constantOneBuffer = createConstantBuffer(context, sampleFrameLength, 1);

        // Create buffer used to control gain.

        linearRampBuffer = createLinearRampBuffer(context, sampleFrameLength);

        // Create the two sources.

        const constantSource = new AudioBufferSourceNode(context, {

          buffer: constantOneBuffer,

});

        const gainChangingSource = new AudioBufferSourceNode(context, {

          buffer: linearRampBuffer,

});

        // Create a gain node controlling the gain of constantSource and make

        // the connections.

        const gainNode = new GainNode(context, {gain: 0});

        constantSource.connect(gainNode).connect(context.destination);

        // Connect an audio-rate signal to control the .gain AudioParam.

        // This is the heart of what is being tested.

        gainChangingSource.connect(gainNode.gain);

        // Start both sources at time 0.

        constantSource.start();

        gainChangingSource.start();

        const renderedBuffer = await context.startRendering();

        checkResult(renderedBuffer);

      }, `AudioParam accepts an audio-rate signal from an AudioNode` +

          ` and scales a constant source exactly`);

    </script>

  </body>

</html>