Voice Over IP

LINEAR PREDICTION ANALYSIS-BY-SYNTHESIS (LPAS) CODERS

The most popular class of speech coders for bit rates between 4.8 and 16 kbit/s are model-based coders that use an LPAS method. A linear prediction model of speech production is excited by an appropriate signal in order to model the signal over time. The parameters of both the speech model and the excitation are estimated and updated at regular time intervals (e.g., every 20 ms) and used to control the speech model. Two LPAS coders are discussed next: the forward-adaptive and backward-adaptive LPAS coders.

Forward-Adaptive LPAS coders: 8-kbit/s G.729 and 6.3- and 5.3-kbit/s G.723.1

In a forward-adaptive AbS coder, the prediction filter coefficients and gains are explicitly transmitted. To ...