Multimode Speech Coding - Digital Speech: Coding for Low Bit Rate Communication Systems - page 316

LSF

LSF
Interpolation

White Noise
Excitation

Received Excitation
Parameters

LSF to LPC
Conversion

ACELP
Excitation

CL1

CL1

LPC
Synthesis
Filter

ˆ( n )

CL2 Harmonic

Excitation

CL2

Figure 9.25 Block diagram of the hybrid decoder

original speech

N N N

A A H

synthesized speech

0 200 400 600 800 1000

samples

Figure 9.26 Synthesized speech and classification: A (ACELP), H (harmonic), and N
(noise excitation)

9.8 Performance Evaluation

The hybrid coder [26] described above has been tested to evaluate its perfor-
mance. The major tasks were developing a reliable classification technique
and preserving the phase continuity when switching between the coding
modes. The classification algorithm is tested using 64 seconds of modified