function createImpulseBuffer(context, numberOfChannels, length) {
  var impulseBuffer = context.createBuffer(
      numberOfChannels, length, context.sampleRate);

  for (var channel = 0; channel < impulseBuffer.numberOfChannels; channel++) {
    var channelData = impulseBuffer.getChannelData(channel);
    channelData[0] = 1.0;
  }

  return impulseBuffer;
}
Create a impulse buffer for testing. Each channel contains a single unity
value (1.0) at the beginning and the rest of content is all zero.
@param  {AudioContext} context     AudioContext
@param  {Number} numberOfChannels  Channel count.
@param  {Number} length            Buffer length in samples.
@return {AudioBuffer}