// This line is a trick to initialize the AudioContext

// that will work on all recent browsers

var ctx = window.AudioContext || window.webkitAudioContext;

var audioContext;

var compressorExemple, gainSlider1, gainNode1, compressorNode;

var compressorButton;

var compressorOn = false;

​

window.onload = function() {

   // get the AudioContext

   audioContext = new ctx();

​

   // the audio element

   compressorExemple = document.querySelector('#compressorExample');

   gainSlider1 = document.querySelector('#gainSlider1');

   // button for turning on/off the compressor

   compressorButton = document.querySelector('#compressorButton');

  buildAudioGraph();

  // input listener on the gain slider

  gainSlider1.oninput = function(evt) {

    gainNode1.gain.value = evt.target.value;

  }; 

  compressorButton.onclick = function(evt) {

      if(compressorOn) {

      // disconnect the compressor and make a 

      // direct route from gain to destination

      compressorNode.disconnect(audioContext.destination);

      gainNode1.disconnect(compressorNode);

      gainNode1.connect(audioContext.destination);

      compressorButton.innerHTML="Turn compressor: On";

    }  else {

      // compressor was off, we connect the gain to the compressor 

      // and the compressor to the destination

      gainNode1.disconnect(audioContext.destination);

      gainNode1.connect(compressorNode);

      compressorNode.connect(audioContext.destination);

      compressorButton.innerHTML="Turn compressor: Off";

    }

    compressorOn = !compressorOn;

  };    

};

​

function buildAudioGraph() {

    // create source and gain node

    var gainMediaElementSource = audioContext.createMediaElementSource(compressorExemple);

    gainNode1 = audioContext.createGain();

    gainNode1.gain.value = parseFloat(gainSlider1.value);

    // do not connect it yet

    compressorNode = audioContext.createDynamicsCompressor();

    // connect nodes together

    gainMediaElementSource.connect(gainNode1);

    gainNode1.connect(audioContext.destination);

}

​

​