Multimode Speech Coding - Digital Speech: Coding for Low Bit Rate Communication Systems - page 297

9.5.2 AdvantagesandDisadvantagesofSWPM
Figure 9.13 shows some examples of waveforms synthesized using the
harmonic excitation technique described in Section 9.5.1. In each example,
(i) represents the LPC residual or the original speech signal and (ii) represents
the LPC excitation or the synthesized speech signal. Figure 9.13a shows the
LPC residual and the harmonic excitation of a segment which has strong
pitch pulses and Figure 9.13b shows the corresponding speech waveforms.
It can be seen that the synthesized speech waveform is very similar to the
original. Figure 9.13c shows the LPC residual and the harmonic excitation
of a segment which has weak or dispersed pitch pulses and Figure 9.13d
shows the corresponding speech waveforms. The synthesized speech is time-
synchronized with the original, however the waveform shapes are slightly

(i)

(i)

(ii)

(ii)

0 100 200 300 400 500 0 100 200 300 400 500

samples samples

(a) LPC residual and excitation signals (b) Speech signals corresponding to (a)

(i)

(i)

(ii)

(ii)

400 500

0 100 200 300 400 500 0 100 200 300

samples samples

(c) LPC residual and excitation signals (d) Speech signals corresponding to (c)

Figure 9.13 synthesized voiced excitation and speech signals