Digital Signal Processing Reference
In-Depth Information
44000.0
(a)
42000.0
40000.0
(b)
38000.0
(c)
36000.0
34000.0
(d)
32000.0
30000.0
(e)
28000.0
26000.0
(f)
24000.0
0.0
500.0
1000.0
1500.0
Time (Samples)
Figure 7.25
Typical CELP waveformplots: (a) codebook contribution, (b) LTP (pitch)
contribution, (c) LPC memory contribution, (d) total output, (e) original speech, and
(f) final error
codebooks, the above codebook type does not require codebook storage and
all codebook search simplifications are applicable. Typical CELP waveforms
which use the above excitation are shown in Figure 7.25. The overall rate of
this coder was around 4.8 kb/s.
7.3.5 JointLTPandCodebookExcitationComputation
In the above analysis, where the pitch predictor contribution and secondary
excitations are computed sequentially, the final LPC excitation which is
formed by adding the pitch predictor contribution and secondary excitations
is suboptimum. When the pitch predictor is optimized, the effect of the
secondary excitation is assumed to be zero. Thus, when the secondary
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