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audioparam-connect-audioratesignal.html (3474B)

      1 <!DOCTYPE html>
      2 <!--
      3 Tests that an audio-rate signal (AudioNode output) can be connected to an
      4 AudioParam.  Specifically, this tests that an audio-rate signal coming from an
      5 AudioBufferSourceNode playing an AudioBuffer containing a specific curve can be
      6 connected to an AudioGainNode's .gain attribute (an AudioParam).  Another
      7 AudioBufferSourceNode will be the audio source having its gain changed.  We load
      8 this one with an AudioBuffer containing a constant value of 1.  Thus it's easy
      9 to check that the resultant signal should be equal to the gain-scaling curve.
     10 -->
     11 <html>
     12  <head>
     13    <title>
     14      audioparam-connect-audioratesignal.html
     15    </title>
     16    <script src="/resources/testharness.js"></script>
     17    <script src="/resources/testharnessreport.js"></script>
     18    <script src="/webaudio/resources/audit-util.js"></script>
     19  </head>
     20  <body>
     21    <script>
     22      const sampleRate = 44100.0;
     23      const lengthInSeconds = 1;
     24 
     25      let context;
     26      let constantOneBuffer;
     27      let linearRampBuffer;
     28 
     29      function checkResult(renderedBuffer) {
     30        const renderedData = renderedBuffer.getChannelData(0);
     31        const expectedData = linearRampBuffer.getChannelData(0);
     32        const n = renderedBuffer.length;
     33 
     34        assert_equals(
     35            n,
     36            linearRampBuffer.length,
     37            'Rendered signal length should match control buffer length');
     38 
     39        // Check that the rendered result exactly matches the buffer used to
     40        // control gain.  This is because we're changing the gain of a signal
     41        // having constant value 1.
     42        let success = true;
     43        for (let i = 0; i < n; ++i) {
     44          if (renderedData[i] != expectedData[i]) {
     45            success = false;
     46            break;
     47          }
     48        }
     49 
     50        assert_true(
     51            success,
     52            `Rendered signal exactly matches ` +
     53                `the audio-rate gain changing signal`);
     54      }
     55 
     56      promise_test(async t => {
     57        const sampleFrameLength = sampleRate * lengthInSeconds;
     58 
     59        // Create offline audio context.
     60        context = new OfflineAudioContext(1, sampleFrameLength, sampleRate);
     61 
     62        // Create buffer used by the source which will have its gain controlled.
     63        constantOneBuffer = createConstantBuffer(context, sampleFrameLength, 1);
     64 
     65        // Create buffer used to control gain.
     66        linearRampBuffer = createLinearRampBuffer(context, sampleFrameLength);
     67 
     68        // Create the two sources.
     69 
     70        const constantSource = new AudioBufferSourceNode(context, {
     71          buffer: constantOneBuffer,
     72        });
     73 
     74        const gainChangingSource = new AudioBufferSourceNode(context, {
     75          buffer: linearRampBuffer,
     76        });
     77 
     78        // Create a gain node controlling the gain of constantSource and make
     79        // the connections.
     80        const gainNode = new GainNode(context, {gain: 0});
     81 
     82        constantSource.connect(gainNode).connect(context.destination);
     83 
     84        // Connect an audio-rate signal to control the .gain AudioParam.
     85        // This is the heart of what is being tested.
     86        gainChangingSource.connect(gainNode.gain);
     87 
     88        // Start both sources at time 0.
     89        constantSource.start();
     90        gainChangingSource.start();
     91 
     92        const renderedBuffer = await context.startRendering();
     93        checkResult(renderedBuffer);
     94      }, `AudioParam accepts an audio-rate signal from an AudioNode` +
     95          ` and scales a constant source exactly`);
     96    </script>
     97  </body>
     98 </html>