The audio signal is processed immediately by the audio control subsystem. This circuit is also responsible for gain control and filtering. A block diagram of the Audio Control's subsystems is seen below.

• A buffer is used to create high input impedance, ensuring maximum voltage transfer from the input. It will be implemented using an operational amplifier (op-amp) circuit.
• The volume control is implemented using an op-amp circuit to provide the input signal with a variable gain. This setup enables the volume at the output to be adjustable with a minimum output of minus-infinity decibels (zero volume).
• The active high and low pass filters are implemented using operational amplifiers to provide a band pass filter. This combination will eliminate unwanted frequencies and pass those that will be converted to sound. Both filters will be second order with cutoff frequencies at 1 kHz and 40 kHz, respectively.
• The active high pass filter also acts as a buffer, which will provide low output impedance to the next subsystem.