setInput(unit) {
    this.input.disconnect();
    this.input = null;
    this.input = ac.createGain();
    this.input.connect(this._workletNode);
    this.input.connect(this.output);
    if (unit) {
      unit.connect(this.input);
    } else {
      p5.soundOut.output.connect(this.input);
    }
  }
Connect a specific device to the p5.SoundRecorder.
 If no parameter is given, p5.SoundRecorer will record
 all audible p5.sound from your sketch.

 @method  setInput
 @for p5.SoundRecorder
 @param {Object} [unit] p5.sound object or a web audio unit
                        that outputs sound