The audio monitor is used to monitor the recorded signal acoustically. Two modes of operation are available. In pitch mode the voltage of the input signal is converted into a tone with a frequency equivalent to the amplitude of the input voltage. It is mostly used in DC recordings. In noise mode the voltage of the input signal is high pass filtered, amplified, and transduced to a sound. It can be used for instance to count action potentials in AC recording mode. A threshold function can be used to blank baseline noise.