What am I working on?
August 27th, 2007 | 
Author: 
What am I working on, you asked?
I’m looking into some voice quality issues on one of our platforms that utilizes a G.729 codec.
What is a G.729 codec?
I’m glad you asked!
A G.729 speech coder is an 8 kbps Conjugate-Structure Algebraic-Code-Excited Linear Prediction (CS-ACELP) speech compression algorithm.
Since G.729 is based on the Code-Excited Linear Prediction (CELP) model, each 80 bit frame produced contains linear prediction coefficients, excitation code book indices, and gain parameters that are used by the decoder in order to reproduce speech. The inputs/outputs of this algorithm are 16 bit linear PCM samples that are converted from/to an 8 kbps compressed data stream.
I’m sure you, too, are glad you asked.
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Oh – well, sorry I asked. Carry on!
But you don’t actually say what the issues are that you are investigating? Random compression failures? How do the issues you are investigating affect speech quality?
@Deannie .. well, it’s a ‘live’ issue and there are customers involved, so I can’t say too much about it. But let me just say that it’s important for codecs to have a steady packetization rate (10 msec for G.729). There are jitter buffers to help in smoothening out temporal variances, but if things get delayed too much somewhere in the stack, things go to hell in a hand basket real fast.