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.

Abstract: The detection sensitivity and noise rejection of an arrangement for detecting speech in the presence of noise is improved by accumulating the weighted differences between input signal samples and their short-term running average. The detector thus tracks ambient noise, providing an adaptive detection threshold such that detection sensitivity is increased in low noise environments without excessive false operation on high level noise. The peak average attained during an interval of speech is used to provide variable hangover upon cessation of speech, yielding greater hangover for weak talkers than for loud talkers. In an illustrative embodiment of the speech detector used in a speech interpolation system, protection is afforded also against false transmission path operation due to detection of speech echo.

Abstract: Known tone detectors are adversely affected by various signaling tone distorting sources, including noise as well as talk-off due to tone-like speech, e.g., due to averaging of speech frequencies over a detection interval. As a result, improper tone detection often occurs. This problem is mitigated by dividing a detection interval into a plurality of detection sub-intervals which are then concatenated for tone detection. Detection of the desired tone in at least a predetermined number of concatenated sub-intervals is interpreted as the presence of a valid tone. Conversely, absence of detection of the desired tone in at least a second predetermined number of concatenated sub-intervals is interpreted as the absence of a valid tone.