_buildImpulse() {
    var rate = this.ac.sampleRate;
    var length = rate * this._seconds;
    var decay = this._decay;
    var impulse = this.ac.createBuffer(2, length, rate);
    var impulseL = impulse.getChannelData(0);
    var impulseR = impulse.getChannelData(1);
    var n, i;
    for (i = 0; i < length; i++) {
      n = this._reverse ? length - i : i;
      impulseL[i] = (Math.random() * 2 - 1) * Math.pow(1 - n / length, decay);
      impulseR[i] = (Math.random() * 2 - 1) * Math.pow(1 - n / length, decay);
    }
    this._setBuffer(impulse);
  }
Inspired by Simple Reverb by Jordan Santell
 https://github.com/web-audio-components/simple-reverb/blob/master/index.js

 Utility function for building an impulse response
 based on the module parameters.

 @private