Analysis by Synthesis LPC Coding - Digital Speech: Coding for Low Bit Rate Communication Systems - page 232

s(n)

W(z)

s w (n)

+

−

Pulse
Generator

+

1/P(z) 1/A w (z)

^

s(n)

e(n)

Error
Minimization

Figure 7.20 Block diagram of MPLPC AbS procedure with LTP

15.0

(a)

(b)

10.0

5.0

0.0

0 2 4 6 8 10

Number of pulses / 32 samples

Figure 7.21 Performance of MPLPC (a) with and (b) without a pitch predictor

which gave optimum values of the pitch predictor where the delay in the
predictor was integer multiples of the pitch. The aim of pitch prediction was
to model the long-term similarities in speech and hence it was also called
the long-term predictor (LTP). The most popular pitch prediction used in
MPLPC is the one-tap predictor. Figure 7.21 shows the objective performance
of the MPLPC with a (one-tap closed-loop) pitch predictor and without a
pitch predictor. It is clear that pitch prediction provides higher segSNR at all