Mitigation of noise signal contrast in a digital speech interpolation transmission system

Abstract

A DSI transmission system is described in which noise signal contrast is mitigated by transmitting not only active channels but also channels which carry background noise, the resolution of the background noise channels being varied in dependence upon the number of channels transmitted. In the described system, the DSI transmission is effected in superframes each of which consists of an overhead information frame and a plurality of digital message frames. The overhead information frame contains a word indicating the transmission status of each channel during the superframe, a code indicating the number of bits of each digital message, and maximum segment value information bits for each of the active channels which are transmitted using nearly instantaneous companding. Each of the remaining frames contains a digital message in respect of each active channel. Remaining space in these frames is occupied by digital messages in respect of the background noise channels, which are allocated to the frames by cyclic assignment and are transmitted using compact PCM encoding. For each superframe, active and background noise channels are determined using speech, echo, and off-hook detectors, and the number of bits of each digital message in the superframe is determined in dependence upon the total number of active and background noise channels.

Dependencies are inferred from the claim text.