The PBL 388 12 contains all the necessary circuitry, amplifiers, detectors, comparators and control functions to implement a high performance, voice-switched, "hands-free " function in an answering machine. The gain dynamics (attenuation between channels) is settable (25dB or 50dB) via CTR pin that also control two mute levels. A background noise detector in the transmitting channel reduces the influence of continuous noise signals. The PBL 388 12 is designed for answering machines that are either powered from the telephone line or from a mains powered dc. supply. Filtering of both the audio and control signals in both transmitter and receiver channels possible.