// 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 convolverSlider, convolverNode, convolverGain, directGain;

var impulseURL = "https://mainline.i3s.unice.fr/mooc/Scala-Milan-Opera-Hall.wav";

var decodedImpulse;

​

window.onload = function() {

   // get the AudioContext

   audioContext = new ctx();

​

    // the audio element

   playerConvolver = document.querySelector('#convolverPlayer');

   playerConvolver.onplay = (e) =>{audioContext.resume();}

      playerConvolver.onplay = (e) => {audioContext.resume();}

​

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

​

  loadImpulse(impulseURL, function() {

    // we get here only when the impulse has finished

    // loading

    buildAudioGraphConvolver();

  });

  // input listener on the gain slider

  convolverSlider.oninput = function(evt){

    // We set the gain at the output of the convolver (wet signal route) with the

    // slider value, and we set the gain between the source and dest

    // (dry signal route) to 1 - wet

    convolverGain.gain.value = parseFloat(evt.target.value);

    directGain.gain.value = 1 - convolverGain.gain.value;

  }; 

};

​

function buildAudioGraphConvolver() {

    // create source and gain node

    var source = audioContext.createMediaElementSource(playerConvolver);

    convolverNode = audioContext.createConvolver();

    convolverNode.buffer = decodedImpulse;

    convolverGain = audioContext.createGain();

    convolverGain.gain.value = 0;

    directGain = audioContext.createGain();

    directGain.gain.value = 1;

    // direct/dry route source -> directGain -> destination

    source.connect(directGain);

    directGain.connect(audioContext.destination);

    // wet route with convolver: source -> convolver 

    // -> convolverGain -> destination

    source.connect(convolverNode);

    convolverNode.connect(convolverGain);

    convolverGain.connect(audioContext.destination);

}

​

function loadImpulse(url, callback) {

  ajaxRequest = new XMLHttpRequest();

  ajaxRequest.open('GET', url, true);

  ajaxRequest.responseType = 'arraybuffer';

​

  ajaxRequest.onload = function() {

    var impulseData = ajaxRequest.response;

​

    audioContext.decodeAudioData(impulseData,  function(buffer) {

        decodedImpulse = buffer;

        callback();

    });

  };

  ajaxRequest.onerror = function(e) {

      console.log("Error with decoding audio data" + e.err);

  };

  ajaxRequest.send();

}