Method for encoding and decoding spectral phase data for speech signals
View Patent ↗A speech decoder and a segment aligner are provided in the present invention. The speech decoder may include a spectrum reconstructor operative to reconstruct the spectrum of a speech segment from the amplitude envelope of the spectrum of said speech segment and pitch information, a phase combiner operative to reconstruct the complex spectrum of the speech segment from the reconstructed spectrum, phase information describing the speech segment, and pitch information describing the speech segment. The speech decoder may further include a delay operative to store a complex spectrum of a previous speech segment; and a segment aligner operative to determine the relative offset between the complex spectrum of the speech segment and the complex spectrum of the previous speech segment, align the position of the first pitch excitation of the current speech segment to the last pitch excitation of the previous speech segment; and to apply a time shift and a complex Hilbert filter to said complex spectra, wherein the segment aligner is operative to cross-correlate the complex spectra as C ( τ ) = ∑ n = 0 N F n G _ m ⅇ - 2 π in τ , m = ⌊ n p G p F + 0.5 ⌋ , where F n and G m are the computed complex magnitude of the pitch harmonics n and m of the current and previous spectra respectively, and p F and p G are their corresponding pitch periods.
1. A speech decoder comprising:
a spectrum reconstructor operative to reconstruct the spectrum of a speech segment from the amplitude envelope of the spectrum of said speech segment and pitch information;
a phase combiner operative to reconstruct the complex spectrum of said speech segment from said reconstructed spectrum, phase information describing said speech segment, and pitch information describing said speech segment;
a delay operative to store a complex spectrum of a previous speech segment; and
a segment aligner operative to:
determine the relative offset between said complex spectrum of said speech segment and the complex spectrum of said previous speech segment;
align the position of the first pitch excitation of said current speech segment to the last pitch excitation of said previous speech segment; and
apply a time shift and a complex Hilbert filter to said complex spectra, wherein said segment aligner is operative to cross-correlate said complex spectra as
C
(
τ
)
=
∑
n
=
0
N
F
n
G
_
m
ⅇ
-
2
π
ⅈ
n
τ
,
m
=
⌊
n
p
G
p
F
+
0.5
⌋
.
where F h , and G m are the computed complex magnitude of the pitch harmonics n and m of the current and previous spectra respectively, and p F and p G are their corresponding pitch periods.
2. A speech decoder according to claim 1 , wherein said segment aligner is operative to cross-correlate on the Hilbert transform of said spectra and sum only the positive frequencies (n,m≧0) of said spectra.
3. A speech decoder according to claim 1 wherein said segment aligner is operative to apply a time shift τ m =arg max{|C(τ)|} and a constant phase shift θ 0 =−arg(C(τ m )) to said current spectrum.
4. A speech decoder according to claim 1 wherein said segment aligner is operative to determine said offset of said current complex spectrum as δ=n p p G −ΔT where there are
n
p
=
⌊
Δ
T
p
G
+
0.5
⌋
pitch cycles in said previous complex spectrum, and where ΔT is the time offset between said complex spectra.
5. A speech decoder according to claim 1 wherein said segment aligner is operative to apply said time shift and said complex Hilbert filter by multiplying F n (t) with e iΔθ n , where Δθ n is given by
Δ
θ
n
=
{
θ
0
+
n
θ
1
n
≥
0
-
θ
0
+
n
θ
1
n
<
0
with
θ
1
=
-
2
π
(
τ
m
+
δ
p
F
)
.
6. A segment aligner comprising:
means for determining the relative offset between a complex spectrum of a speech segment and a complex spectrum of a previous speech segment;
means for aligning the position of the first pitch excitation of said current speech segment to the last pitch excitation of said previous speech segment; and
means for applying a time shift and a complex Hilbert filter to said complex spectra,
wherein said means for determining is operative to cross-correlate said complex spectra as
C
(
τ
)
=
∑
n
=
0
N
F
n
G
_
m
ⅇ
-
2
π
ⅈ
n
τ
,
m
=
⌊
n
p
G
p
F
+
0.5
⌋
,
where F n and G m are the computed complex magnitude of the pitch harmonics n and m of the current and previous spectra respectively, and p F and p G are their corresponding pitch periods.
7. A segment aligner according to claim 6 wherein said means for determining is operative to cross-correlate on the Hubert transform of said spectra and sum only the positive frequencies (n,m ≧0) of said spectra.
8. A segment aligner according to claim 6 wherein said means for aligning is operative to apply a time τ m =arg max{|C(τ)|} and a constant phase shift θ 0 =−arg(C(τ m )) to said current spectrum.
9. A segment aligner according to claim 6 wherein said means for determining is operative to determine said offset of said current complex spectrum as δ=n p p G −ΔT where there are
n
p
=
⌊
Δ
T
p
G
+
0.5
⌋
pitch cycles in said previous complex spectrum, and where ΔT is the time offset between said complex spectra.
10. A segment aligner according to claim 6 wherein said means for aligning is operative to apply said time shift and said complex Hilbert filter by multiplying F n (t) with e iΔθ n , where Δθ n is given by
Δ
θ
n
=
{
θ
0
+
n
θ
1
n
≥
0
-
θ
0
+
n
θ
1
n
<
0
with
θ
1
=
-
2
π
(
τ
m
+
δ
p
F
)
.