Basically, the circuit always makes the sound loud enough for the patient to hear, but should never get louder than what the patient has indicated is uncomfortable for them to listen to. A programmable circuit is much more sophisticated than the linear and basic compression circuits. A programmable, as its name implies is programmed through a computer, thus it is digitally programmable. The circuit itself, however, does not process the information coming into it digitally. It is still an analog processor.
Most programmable circuits have at least two channels.
Each channel of the program is controlled independently of the others, and each channel controls a certain range of pitches coming into the hearing instrument. This allows the Audiologist very fine tuning ability to match the patient's hearing loss and to filter out sounds such as background noise to give the patient a clearer speech signal. When in the omnidirectional mode it functions much like the programmable circuit. However, when in the directional mode, it has the added affect of dampening the sounds around you and amplifying the sounds directly in front of you. This directional mode would be utilized in a noisy restaurant, for example, to help you focus in on what the person or people you are with are saying, while dampening the chatter around you.