Digital Signal Processing Reference
In-Depth Information
n
p
w
r
(
n
)
R
j
Cross
Correlation
Computation
Probability
Function
n
pw
α
Prototype
Pulse
Generation
a
k
q
w
Final Pitch
Pulse
on/off
p
(
n
s
)
ω
E
j
SNR
Computation
Shape
History
n
0
α
0
t
0
Refine PPL
and PPS
n
p
w
n
lst
α
α
r
(
n
)
t
0
lst
a
k
ω
r
(
n
)
u
Figure 9.9
Block diagram of the pitch pulse shape estimation
0
10
20
30
0
10
20
30
samples
samples
(a)
q
=
0
α
(a)
q
=
π
/2
α
Figure 9.10
synthesized pulses,
p (n
s
)
each harmonic, which is beneficial in estimating the pitch pulse shape. For
example, if a harmonic component which is relatively small in the LPC
residual signal is given equal weight in the prototype pulse,
p(n
s
)
,this
may lead to inaccurate estimates in the subsequent AbS refinement process.
Considering the frequency domain, those relatively small amplitudes may be
affected by spectral leakage from the larger amplitudes, giving large errors in
the phase spectrum. However, since computing the spectral amplitudes for
each pitch pulse is a very intensive process, as a compromise, the same spectral
amplitudes are used for the whole analysis frame, and are also transmitted
to the decoder as the harmonic amplitudes of the LPC residual. Then the
normalized cross-correlation,
R
j
,andSNR,
E
j
, are estimated between the
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