Fixed codebook searching apparatus and fixed codebook searching method
View Patent ↗A fixed codebook searching apparatus which slightly suppresses an increase in the operation amount, even if the filter applied to the excitation pulse has the characteristic that it cannot be represented by a lower triangular matrix and realizes a quasi-optimal fixed codebook search. This fixed codebook searching apparatus is provided with an algebraic codebook that generates a pulse excitation vector; a convolution operation section that convolutes an impulse response of auditory weighted synthesis filter into an impulse response vector that has a value at negative times, to generate a second impulse response vector that has a value at second negative times; a matrix generating section that generates a Toeplitz-type convolution matrix by means of the second impulse response vector; and a convolution operation section that convolutes the matrix generated by matrix generating section into the pulse excitation vector generated by algebraic codebook.
1. A fixed codebook searching apparatus, comprising:
a convolution operator, implemented by at least one processor, that convolves an impulse response of a perceptually weighted synthesis filter with an impulse response vector that has values at negative times, to generate a second impulse response vector that has values at negative times;
a matrix generator, implemented by the at least one processor, that generates a Toeplitz-type convolution matrix using the second impulse response vector generated by the convolution operator; and
a searcher, implemented by the at least one processor, that performs a fixed codebook search by maximizing a term using the Toeplitz-type convolution matrix.
2. The fixed codebook searching apparatus according to claim 1 , wherein the Toeplitz-type convolution matrix is shown by matrix H′
H
′
=
[
h
(
0
)
(
0
)
…
h
(
0
)
(
-
m
)
0
0
h
(
0
)
(
1
)
⋱
⋮
⋱
0
⋮
h
(
0
)
(
0
)
h
(
0
)
(
-
m
)
⋮
⋮
⋱
⋮
h
(
0
)
(
N
-
1
)
…
h
(
0
)
(
N
-
1
-
m
)
…
h
(
0
)
(
0
)
]
where h (0) (n) is the second impulse response vector (n=−m, . . . ,0, . . . , N−1) that has values at negative times.
3. The fixed codebook searching apparatus according to claim 1 , wherein the searcher minimizes an error between a target vector for the fixed codebook search and a perceptually weighted synthesis signal obtained by multiplying a pulse vector outputted from an algebraic codebook by the Toeplitz-type convolution matrix.
4. The fixed codebook searching apparatus according to claim 1 , wherein the term using the Toeplitz-type convolution matrix is shown by the following expressions:
C
k
2
E
k
2
=
(
∑
n
=
0
N
-
1
d
′
(
n
)
c
k
(
n
)
)
2
c
k
′
Φ
′
c
k
d
′
(
i
)
=
{
∑
n
=
-
i
N
-
1
-
i
x
(
n
+
i
)
h
(
0
)
(
n
)
,
where
i
=
0
,
…
,
m
-
1
∑
n
=
-
m
N
-
1
-
i
x
(
n
+
i
)
h
(
0
)
(
n
)
,
where
i
=
m
,
…
,
n
-
1
ϕ
′
(
i
,
j
)
=
{
∑
n
=
-
i
N
-
1
-
i
h
(
0
)
(
n
)
h
(
0
)
(
n
)
,
where
i
=
j
=
0
,
…
,
m
-
1
ϕ
′
(
j
,
i
)
=
∑
n
=
-
m
N
-
1
-
j
h
(
0
)
(
n
+
j
-
i
)
h
(
0
)
(
n
)
,
where
i
=
m
,
…
,
N
-
1
,
j
=
i
,
…
N
-
1
where:
C k is a pulse excitation vector specified by an index k;
c k (n) is an n-th vector element of a vector c k ;
x(n) is an n-th element of the target vector;
h (0) (n) is an n-th element of the second impulse response vector; and
φ′(i,j) is an i-th row j-th column element (an i-j element) of a matrix Φ′.