Apparatus for mitigating signal distortion and noise signal contrast in

Abstract

In a communications system such as a time assignment speech interpolation (TASI) system for concentrating signals from N trunks onto C channels (C < N), and for expanding same, it is common for a speech signal to pass through a plurality of transmitter/receiver terminals, perhaps connected for tandem operation. Unfortunately, transmitter speech detector clipping of the speech signal leads to a distortion accumulation problem. Also, while a calling trunk is inactive, an inserted noise signal is commonly furnished by a receiver to the called trunk to avoid an aural 'too quiet' condition. Unfortunately, actual calling trunk noise and the called trunk inserted noise may differ, leading to a noise signal contrast problem. To mitigate the signal contrast problem, communications apparatus including an improved noise signal inserting arrangement, responsive to a measure of calling trunk noise, supplies an adaptively adjusted, deterministic, pseudorandom noise signal to the called trunk. Thereafter, the presence or absence of the deterministic signal may be detected at a tandem transmitter and, responsive to its absence, the speech detector, at the tandem transmitter is overridden to mitigate the distortion accumulation of speech signal clipping.