Abstract: Idle channel noise reduction is achieved in a line card having an analog gain/attenuator, a codec, and a digital signal processor including an equalizer and a digital gain/attenuator. A peak detector samples output from the codec each 8 kHz cycle. A level decision compares the sample to a stored peak value, and replaces the stored peak value with the sample if it is greater. A controller, at a second predetermined interval, increases analog gain in steps and increases digital attenuation in similar steps if the stored peak value is greater than the predetermined threshold. Otherwise, the controller increases analog attenuation in steps and increases digital gain in similar steps.

Abstract: A private local area network (LAN) is created for use with a variety of transmission media for the purpose of exchanging data preassigned addresses, and control signals according to simplified protocols. The LAN members can consist of any combination of computers, electronic devices or terminals adapted for intercommunication via microprocessor-based modems which are capable of performing either master or slave functions within the LAN in accordance with their individual software designations. Each modem operating on the LAN has the capability of filtering analog noise, detecting/blocking digital data errors, operating within a wide range of appropriate line impedances, and both transmitting and receiving digital data at rates in the neighborhood of 85 kbaud in the form of frequency, or tone, bursts according to a hybrid ASK/FSK data encoding an transmission scheme.