System for transmission of coded speech signals

摘要

Received codewords are entered (11) in a decoder (12) which generates digital speech data on a line (13) to a controllable attenuator (26) feeding the signal via a digital-to-analogue converter (30) to a loudspeaker (34). In the opposite direction the output of a microphone (32) is digitised (28) and a filtered (20) version of the first digital signal (27) is subtracted (22), leaving a remainder to pass through another controllable attenuator (24) to an encoder (14) for transmission (15). The attenuators are controlled and the digital filter coeffts. adjusted by a processor (16).