2010318163752818

ISO/IEC 14496-3:2005(E)
2.B.1.3.2 Unvoiced speech
Spectral shaping:
Pf z
uv
n −n
∑αγ
n z
n=
0
( ) −1
= P ( 1 −δz)
n −n
∑αnβ
z
84 © ISO/IEC 2005 — All rights reserved
P
n=
0
Similarly the transfer function of the spectral shaping filter for unvoiced speech is given as Pf uv ( z)
, where αn are
linear predictive coefficients converted from de-quantized LSPs, which are updated every 20 ms. When normal
decode mode is selected, LSP coefficients are updated at the middle of decode frame interval. If low delay decode
mode is selected , decode frame interval is shifted by 2.5 ms and LSP update happens at 7.5 ms point from the
beginning of the decode interval in Figure 2.9 p = 10, γ = 05 . , β = 08 . , δ = 01 . . The gain adjustment and the
smoothing process are the same as in the voiced part described above, and produces postfiltered unvoiced
speech uvspeech( n).
The output of each of the postfilters, vspeech( n)
and uvspeech( n)
are added to generate postfiltered speech output.
2.B.2 Post processing
2.B.2.1 Tool description
The output of the postfilter is fed into the post processing part. Post processing is composed of three filters, those
are, high pass filter, high frequency emphasis filter, and low pass filter. High pass filter is used to remove
unnecessary low frequency components, high frequency emphasis is used to increase the brightness of the
speech, and low pass filter is used to remove unnecessary high frequency components. The filter configurations
and constants described here is one example and not normative, and they could be modified.
2.B.2.2 Definitions
HPF(): z Transfer function of high pass filter.
Emp(): z Transfer function of high frequency emphasis filter.
LPF(): z Transfer function of low pass filter.
2.B.2.3 Processing
The three filters below are applied to the output of the postfilter.
High Pass Filter:
HPF()= z G
inv
−1−2 1 + Az 1 + Bz 1
1
1 + Cz + Dz
− −2
1 1
−1−2 1 + Az 2 + Bz 2
⋅
1
1+
Cz + Dz
− −2
2 2