audioparam-summingjunction.html

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    <title>

      audioparam-summingjunction.html

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

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

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

    <script src="/webaudio/resources/mix-testing.js"></script>

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    <script>

      // Tests that multiple audio-rate signals (AudioNode outputs)

      // can be connected to an AudioParam and that these signals

      // are summed, along with the AudioParams intrinsic value.

      const sampleRate = 44100.0;

      const lengthInSeconds = 1;

      // Buffers used by the two gain controlling sources.

      let linearRampBuffer;

      let toneBuffer;

      const toneFrequency = 440;

      // Arbitrary non-zero value.

      const baselineGain = 5;

      const maxAllowedError = 1e-6;

      function checkResult(renderedBuffer) {

        let renderedData = renderedBuffer.getChannelData(0);

        // Get buffer data from the two sources used to control gain.

        const linearRampData = linearRampBuffer.getChannelData(0);

        const toneData = toneBuffer.getChannelData(0);

        const n = renderedBuffer.length;

        assert_equals(n, linearRampBuffer.length, 'Rendered signal length');

        // Check that the rendered result exactly matches the sum of the

        // intrinsic gain plus the two sources 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) {

          const expectedValue = baselineGain + linearRampData[i] + toneData[i];

          const error = Math.abs(expectedValue - renderedData[i]);

          if (error > maxAllowedError) {

            success = false;

            break;

        assert_true(

            success,

            'Rendered signal matches sum of two audio-rate gain changing ' +

                'signals plus baseline gain'

);

      promise_test(async t => {

        const sampleFrameLength = sampleRate * lengthInSeconds;

        const context =

            new OfflineAudioContext(1, sampleFrameLength, sampleRate);

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

        const constantOneBuffer =

            createConstantBuffer(context, sampleFrameLength, 1);

        let constantSource = new AudioBufferSourceNode(context);

        constantSource.buffer = constantOneBuffer;

        // Create 1st buffer used to control gain (a linear ramp).

        linearRampBuffer = createLinearRampBuffer(context, sampleFrameLength);

        let gainSource1 = new AudioBufferSourceNode(context);

        gainSource1.buffer = linearRampBuffer;

        // Create 2st buffer used to control gain (a simple sine wave tone).

        toneBuffer =

            createToneBuffer(context, toneFrequency, lengthInSeconds, 1);

        let gainSource2 = new AudioBufferSourceNode(context);

        gainSource2.buffer = toneBuffer;

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

        // the connections.

        let gainNode = new GainNode(context);

        // Intrinsic baseline gain.

        // This gain value should be summed with gainSource1 and gainSource2.

        gainNode.gain.value = baselineGain;

        constantSource.connect(gainNode);

        gainNode.connect(context.destination);

        // Connect two audio-rate signals to control the .gain AudioParam.

        gainSource1.connect(gainNode.gain);

        gainSource2.connect(gainNode.gain);

        // Start all sources at time 0.

        constantSource.start(0);

        gainSource1.start(0);

        gainSource2.start(0);

        const renderedBuffer = await context.startRendering();

        checkResult(renderedBuffer);

      }, 'Test summing junction behavior of AudioParam with multiple ' +

          'audio-rate sources and intrinsic gain');

    </script>

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