DIGITAL VOICE COMPRESSION HAVING A DIGITALLY CONTROLLED AGC CIRCUIT AND MEANS FOR INCLUDING THE TRUE GAIN IN THE COMPRESSED DATA

摘要

Digital communication apparatus for use, with telephone lines, and having a digitally controlled Automatic Gain Control (AGC) circuit and means for including the true gain in the compressed data is described. At a transmitting end of a telephone link, a linear prediction coding analyser is interfaced with a digital-to-analog AGC and which controls the AGC to maintain the linear prediction coding analyser within a range of gain settings to ensure that a linear predicting encoding algorithm is properly utilised. The gain information transmitted each frame is also adjusted by the same amount to reflect the actual gain of the digitised voice signal for proper synthesis at the receiver end. Echo suppression is also described.