stop() {
    if (this.stream) {
      this.stream.getTracks().forEach(function (track) {
        track.stop();
      });

      this.mediaStream.disconnect();

      delete this.mediaStream;
      delete this.stream;
    }
  }
Turn the AudioIn off. If the AudioIn is stopped, it cannot getLevel().
 If re-starting, the user may be prompted for permission access.

 @method stop
 @for p5.AudioIn