Getting Started with Web Audio

The Web Audio API is a JavaScript based API for sound synthesis and processing in web applications. It is compatible to most browsers and can thus be used on almost any device. This makes it a powerful tool in many areas. In the scope of this introduction it is introduced as a means for data sonification with web-based data APIs and for interactive sound examples. Read the W3C Candidate Recommendation for an in-depth documentation.

The Sine Example

The following Web Audio example features a simple sine wave oscillator with frequency control and a mute button:

Sine Example

Sine Example.

Frequency

Code

Building Web Audio projects involves three components:

  • HTML for control elements and website layout
  • CSS for website appearance
  • JavaScript for audio processing

Since HTML is kept minimal, the code is compact but the GUI is very basic.

sine_example/sine_example.html (Source)

<!doctype html>
<html>

<head>
  <title>Sine Example</title>

  <!-- embedded CSS for slider appearance -------------------------------------->

  <style>
  /* The slider look */
  .minmalslider {
    -webkit-appearance: none;
    appearance: none;
    width: 100%;
    height: 25px;
    background: #d3d3d3;
    outline: none;
  }
  </style>
</head>

<!-- HTML control elements  --------------------------------------------------->

<blockquote style="border: 2px solid #122; padding: 10px; background-color: #ccc;">

  <body>
    <p>Sine Example.</p>
    <p>
      <button onclick="play()">Play</button>
      <button onclick="stop()">Stop</button>
      <span>
        <input  class="minmalslider"  id="pan" type="range" min="10" max="1000" step="1" value="440" oninput="frequency(this.value);">
        Frequency
      </span>
    </p>
  </body>

</blockquote>


<!-- JavaScript for audio processing ------------------------------------------>

  <script>

    var audioContext = new window.AudioContext
    var oscillator = audioContext.createOscillator()
    var gainNode = audioContext.createGain()

    gainNode.gain.value = 0

    oscillator.connect(gainNode)
    gainNode.connect(audioContext.destination)

    oscillator.start(0)

    // callback functions for HTML elements
    function play()
    {
      gainNode.gain.value = 1
    }
    function stop()
    {
      gainNode.gain.value = 0
    }
    function frequency(y)
    {
      oscillator.frequency.value = y
    }

  </script>
</html>

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