function AudioBus (numberOfChannels, length, sampleRate) {
  this.numberOfChannels = numberOfChannels;
  this.sampleRate = sampleRate;
  this.length = length;
  this.duration = this.length / this.sampleRate;

  this._channelData = [];
  for (var i = 0; i < this.numberOfChannels; ++i) {
    this._channelData[i] = new Float32Array(length);
  }
}
A collection of Float32Array as AudioBus abstraction.
@param {Number} numberOfChannels   Number of channels.
@param {Number} length             Buffer length in samples.
@param {Number} sampleRate         Operating sample rate.