Efficient LPC Quantization Methods - Digital Speech: Coding for Low Bit Rate Communication Systems - page 137

12

f
g

10

8

6

4

2

0 0.2 0.4 0.6 0.8 1

Prediction Parameter

Figure 5.28 Moving average LSF prediction residual variance for 40ms LSF
vector rate

Table 5.14 Prediction gain for low-pass filtered
and classic LSF extractionmethods at various vec-
tor rates

LSF vector transmission rate

40ms 30ms 20ms 10ms 5ms

P g for g

29.55 33.82 36.53 43.34 49.57

P g for f 12.50 16.60 29.60 37.60 42.60

where x 0 is the variance of LSF prediction residual when the prediction
factor is zero (the original LSF variance) and x min is the minimum variance
of LSF prediction residual computed by selecting the optimum prediction
coefficient. Higher P g is an indication of performance improvement that can
be achieved through MA prediction before quantization. Table 5.14 shows
the value of prediction gains at different LSF vector transmission rates. The