Methods for improving the signal to total distortion and gain variation with level for PCM transmission and switching systems

摘要

It is desirable to utilize the ability of a DSP to perform signal processing within PCM transmission or switching systems.The DSP can be part of the common equipment,which is shared by many channels in the system to provide cost- effective signal processing functions.The 8-bit architectue of most PCM equipment forces the companding functions to reside in CODECs on the line or trunk cards.The DSP does not have access to linearly coded samples,and instead must deal with mu-law or A-law encoded samples.Problems in meeting ITU G.712 [12] specifications arise when the DSP block performs an additional expand and compress function on the channel.This paper addresses issues associated with two of these problems:Signal to Total Distortion (S/D) G.712, para 12,and Gain Variation with Level (G vs.L) G.712 para 13. Both of these tests require injecting and measuring signals over a wide dynamic range.