Source: http://www.google.com/patents/US8150702?ie=ISO-8859-1&dq=6181294
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Patent US8150702 - Stereo audio encoding device, stereo audio decoding device, and method thereof - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsDisclosed is a stereo audio encoding device capable of improving a spatial image of a decoded audio in stereo audio encoding. In this device, an original cross correlation calculation unit (101) calculates a mutual relationship coefficient (C1) between the original L channel signal and the original R...http://www.google.com/patents/US8150702?utm_source=gb-gplus-sharePatent US8150702 - Stereo audio encoding device, stereo audio decoding device, and method thereofAdvanced Patent SearchPublication numberUS8150702 B2Publication typeGrantApplication numberUS 12/376,000Publication dateApr 3, 2012Filing dateAug 2, 2007Priority dateAug 4, 2006Also published asEP2048658A1, EP2048658A4, EP2048658B1, US20090299734, WO2008016097A1Publication number12376000, 376000, US 8150702 B2, US 8150702B2, US-B2-8150702, US8150702 B2, US8150702B2InventorsJiong Zhou, Kok Seng ChongOriginal AssigneePanasonic CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (18), Non-Patent Citations (6), Referenced by (3), Classifications (9), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetStereo audio encoding device, stereo audio decoding device, and method thereofUS 8150702 B2Abstract Disclosed is a stereo audio encoding device capable of improving a spatial image of a decoded audio in stereo audio encoding. In this device, an original cross correlation calculation unit (101) calculates a mutual relationship coefficient (C1) between the original L channel signal and the original R channel signal. A stereo audio reconfiguration unit (104) subjects the inputted L channel signal and the R channel signal to encoding and decoding so as to generate an L channel reconfigured signal (L′) and an R channel reconfigured signal (R′). A reconfiguration cross correlation calculation unit (105) calculates a cross correlation coefficient (C2) between the L channel reconfigured signal (L′) and the R channel reconfigured signal (R′). A cross correlation comparison unit (106) calculates and outputs a comparison result &agr; between the cross correlation coefficient (C1) and the cross correlation coefficient (C2).
The invention claimed is: 1. A stereo speech coding apparatus comprising:
a first calculation section that calculates a first cross-correlation coefficient between a first channel signal and a second channel signal constituting stereo speech;
a stereo speech reconstruction section that generates a first channel reconstruction signal and a second channel reconstruction signal using the first channel signal and the second channel signal;
a second calculation section that calculates a second cross-correlation coefficient between the first channel reconstruction signal and the second channel reconstruction signal; and
a comparison section that acquires a cross-correlation comparison result comprising spatial information of the stereo speech by comparing the first cross-correlation coefficient and the second cross-correlation coefficient.
2. The stereo speech coding apparatus according to claim 1, wherein:
the first calculation section calculates the first cross-correlation coefficient according to equation 1
C 1 = ∑ n ⁢ L ⁡ ( n ) ⁢ R ⁡ ( n ) ∑ n ⁢ L ⁡ ( n ) 2 ⁢ ∑ n ⁢ R ⁡ ( n ) 2 ( Equation ⁢ ⁢ 1 ) where
C 2 = ∑ n ⁢ L ′ ⁡ ( n ) ⁢ R ′ ⁡ ( n ) ∑ n ⁢ L ′ ⁡ ( n ) 2 ⁢ ∑ n ⁢ R ′ ⁡ ( n ) 2 ( Equation ⁢ ⁢ 2 ) where
α = C 1 C 2 ( Equation ⁢ ⁢ 3 ) where
a monaural signal generation section that generates a monaural signal using the first channel signal and the second channel signal; and
a monaural signal coding section that generates a monaural signal coded parameter by encoding the monaural signal,
wherein the stereo speech reconstruction section generates the first channel reconstruction signal and the second channel reconstruction signal by applying the monaural signal and the monaural signal coded parameter to the first channel signal and the second channel signal.
4. The stereo speech coding apparatus according to claim 3, wherein the stereo speech reconstruction section comprises:
a first adaptive filter that finds a first adaptive filter parameter to minimize a mean square error between the monaural signal and the first channel signal;
a second adaptive filter that finds a second adaptive filter parameter to minimize a mean square error between the monaural signal and the second channel signal;
a monaural signal decoding section that generates a decoded monaural signal by decoding the monaural signal using the monaural signal coded parameter;
a first synthesis filter that generates the first channel reconstruction signal by filtering the decoded monaural signal by the first adaptive filter parameter; and
a second synthesis filter that generates the second channel reconstruction signal by filtering the decoded monaural signal by the second adaptive filter parameter.
5. A stereo speech decoding apparatus comprising:
a separation section that acquires, from a bit stream that is received as input, a first parameter and a second parameter, related to a first channel signal and a second channel signal, respectively, the first channel signal and the second channel signal being generated in a coding apparatus and constituting stereo speech, and a cross-correlation comparison result that is acquired by comparing a first cross-correlation between the first channel signal and the second channel signal and a second cross-correlation between a first channel reconstruction signal and a second channel reconstruction signal generated using the first channel signal and the second channel signal, the cross-correlation comparison result comprising spatial information related to the stereo speech;
a stereo speech decoding section that generates a decoded first channel reconstruction signal and a decoded second channel reconstruction signal using the first parameter and the second parameter;
a stereo reverberant signal generation section that generates a first channel reverberant signal using the decoded first channel reconstruction signal and generates a second channel reverberant signal using the decoded second channel reconstruction signal;
a first spatial information recreation section that generates a first channel decoded signal using the decoded first channel reconstruction signal, the first channel reverberant signal and the cross-correlation comparison result; and
a second spatial information recreation section that generates a second channel decoded signal using the decoded second channel reconstruction signal, the second channel reverberant signal and the cross-correlation comparison result.
6. The stereo speech decoding apparatus according to claim 5, wherein the stereo reverberant signal generation section comprises:
a first allpass filter that generates the first channel reverberant signal by allpass filtering the decoded first channel reconstruction signal; and
a second allpass filter that generates the second channel reverberant signal by allpass filtering the decoded second channel reconstruction signal.
7. A stereo speech decoding apparatus comprising:
a monaural reverberant signal generation section that generates a monaural reverberant signal using the decoded first channel reconstruction signal and the decoded second channel reconstruction signal;
a first spatial information recreation section that generates a first channel decoded signal using the decoded first channel reconstruction signal, the monaural reverberant signal and the cross-correlation comparison result; and
a second spatial information recreation section that generates a second channel decoded signal using the decoded second channel reconstruction signal, the monaural reverberant signal and the cross-correlation comparison result.
8. The stereo speech decoding apparatus according to claim 7, wherein the monaural reverberant signal generation section comprises:
a monaural signal generation section that generates a monaural reconstruction signal using the decoded first channel reconstruction signal and the decoded second channel reconstruction signal; and
a monaural signal allpass filter that generates the monaural reverberant signal by allpass filtering the monaural reconstruction signal.
9. A stereo speech coding method comprising the steps of:
calculating a first cross-correlation coefficient between a first channel signal and a second channel signal constituting stereo speech;
generating a first channel reconstruction signal and a second channel reconstruction signal using the first channel signal and the second channel signal;
calculating a second cross-correlation coefficient between the first channel reconstruction signal and the second channel reconstruction signal; and
acquiring a cross-correlation comparison result comprising spatial information of the stereo speech, by comparing the first cross-correlation coefficient and the second cross-correlation coefficient.
10. A stereo speech decoding method comprising the steps of:
acquiring, from a bit stream that is received as input, a first parameter and a second parameter, related to a first channel signal and a second channel signal, respectively, the first channel signal and the second channel signal being generated in a coding apparatus and constituting stereo speech, and a cross-correlation comparison result that is acquired by comparing a first cross-correlation between the first channel signal and the second channel signal and a second cross-correlation between a first channel reconstruction signal and a second channel reconstruction signal generated using the first channel signal and the second channel signal, the cross-correlation comparison result comprising spatial information related to the stereo speech;
generating a decoded first channel reconstruction signal and a decoded second channel reconstruction signal using the first parameter and the second parameter;
generating a first channel reverberant signal using the decoded first channel reconstruction signal and generating a second channel reverberant signal using the decoded second channel reconstruction signal;
generating a first channel decoded signal using the decoded first channel reconstruction signal, the first channel reverberant signal and the cross-correlation comparison result; and
generating a second channel decoded signal using the decoded second channel reconstruction signal, the second channel reverberant signal and the cross-correlation comparison result.
11. A stereo speech decoding method comprising the steps of:
generating a monaural reverberant signal using the decoded first channel reconstruction signal and the decoded second channel reconstruction signal;
generating a first channel decoded signal using the decoded first channel reconstruction signal, the monaural reverberant signal and the cross-correlation comparison result; and
generating a second channel decoded signal using the decoded second channel reconstruction signal, the monaural reverberant signal and the cross-correlation comparison result. Description
Non-Patent Document 2: ISO/IEC 23003-1: 2006/FCD MPEG Surround (ISO/IEC 23003-1: 2007 Part1 MPEG Surround)
DISCLOSURE OF INVENTION Problems to be Solved by the Invention When a stereo audio signal is encoded, three inter-channel cues, namely ILD, ITD and ICC, are calculated and encoded. By contrast with this, when stereo speech is encoded, only two inter-channel cues, namely ILD and ITD, are encoded. ICC is important spatial information included in stereo speech signals, and, if stereo speech is generated in the decoding end without utilizing ICC, the stereo speech lacks spatial images. It necessarily follows that, to improve the spatial images of decoded stereo signals, a configuration for encoding ILD, ITD, and, in addition, spatial information, needs to be introduced in stereo speech coding.
( Equation ⁢ ⁢ 1 ) C 1 = ∑ n ⁢ L ⁡ ( n ) ⁢ R ⁡ ( n ) ∑ n ⁢ L ⁡ ( n ) 2 ⁢ ∑ n ⁢ R ⁡ ( n ) 2 [ 1 ] where
( Equation ⁢ ⁢ 2 ) M ⁡ ( n ) = 1 2 ⁡ [ L ⁡ ( n ) + R ⁡ ( n ) ] [ 2 ] where
( Equation ⁢ ⁢ 3 ) C 2 = ∑ n ⁢ L ′ ⁡ ( n ) ⁢ R ′ ⁡ ( n ) ∑ n ⁢ L ′ ⁡ ( n ) 2 ⁢ ∑ n ⁢ R ′ ⁡ ( n ) 2 [ 3 ] where
( Equation ⁢ ⁢ 4 ) α = C 1 C 2 [ 4 ] where C1 is the cross-correlation coefficient between the L channel signal and the R channel signal;
( Equation ⁢ ⁢ 5 ) M ⁢ ⁢ S ⁢ ⁢ E ⁡ ( b ) = E ⁢ { [ e ⁡ ( n ) ] 2 } ⁢ ⁢ = E ⁢ { [ y ⁡ ( n ) - y ′ ⁡ ( n ) ] 2 } ⁢ ⁢ = E ⁢ { [ y ⁡ ( n ) - ∑ i = 0 k ⁢ b i ⁢ x ⁡ ( n - i ) ] 2 } [ 5 ] In this equation, E is the statistical expectation operator, e(n) is the prediction error, and k is the filter order.
As described above, stereo speech coding apparatus 100 transmits the adaptive filter parameters found in L channel adaptive filter 141 and in R channel adaptive filter 142 to stereo speech decoding apparatus 200, as spatial information parameters related to inter-channel level difference (ILD) and inter-channel time difference (ITD). Furthermore, stereo speech coding apparatus 100 transmits to stereo speech decoding apparatus 200 the cross-correlation comparison result α found in cross-correlation comparison section 106 as spatial information parameters related to inter-channel cross-correlation (ICC) between the L channel signal and the R channel signal.
Incidentally with the present embodiment, stereo speech coding apparatus 100 may transmit the cross-correlation coefficient C1 between the original L channel signal (L) and R channel signal (R), instead of the cross-correlation comparison result α. In this case, it is still possible to determine the cross-correlation coefficient C2 between the L channel reconstruction signal (L′) and the R channel reconstruction signal (R′) in the decoder end, so that the cross-correlation comparison result α can be calculated in the decoder end. By this means, in stereo speech coding apparatus 100, it is no longer necessary to generate reconstruction signals of the L channel and R channel, so that the amount of calculations can be reduced.
Separation section 201 performs separation processing with respect to a bit stream received as input from stereo speech coding apparatus 100, outputs the monaural signal coded parameters, L channel adaptive filter parameters and R channel adaptive filter parameters to stereo speech decoding section 202, and outputs the cross-correlation comparison result α to L channel spatial information recreation section 205 and R channel spatial information recreation section 206.
( Equation ⁢ ⁢ 6 ) H allpass = a N + a N - 1 ⁢ z - 1 + � + a 1 ⁢ z - ( N - 1 ) + z - N 1 + a 1 ⁢ z - 1 + � + a N - 1 ⁢ z - ( N - 1 ) + a N ⁢ z - N [ 6 ] In this equation, Hallpass is the transfer function of the allpass filter, a=[a1, a2, . . . , aN] is the allpass filter parameters, and N is the order of the allpass filter parameters. The input signal L′ in L channel allpass filter 203 and the output signal L′Rev are orthogonal to each other, so that the cross-correlation value between them is [L′ (n), L′Rev(n)]=0. The energy of L′ and the energy of L′Rev are the same, that is, |L′(n)|2=|L′Rev(n)|2.
L channel spatial information recreation section 205 calculates and outputs a decoded L channel signal (L″) using the cross-correlation comparison result α received as input from separation section 201, the L channel reconstruction signal (L′) received as input from stereo speech decoding section 202, and the L channel reverberant signal (L′Rev) received as input from L channel allpass filter 203, according to equation 7 below.
R channel spatial information recreation section 206 calculates and outputs a decoded R channel signal (R″) using the cross-correlation comparison result α received as input from separation section 201, the R channel reconstruction signal (R′) received as input from stereo speech decoding section 202, and the R channel reverberant signal (R′Rev) received as input from R channel allpass filter 204, according to equation 8 below.
( Equation ⁢ ⁢ 12 ) C 3 = ∑ n ⁢ L ″ ⁡ ( n ) ⁢ R ″ ⁡ ( n ) ∑ n ⁢ L ″ ⁡ ( n ) 2 ⁢ ⁢ ∑ n ⁢ R ″ ⁡ ( n ) 2 = α 2 ⁢ C 2 = C 1 [ 12 ] FIG. 8 is a block diagram showing primary configurations inside stereo speech decoding section 202.
( Equation ⁢ ⁢ 13 ) α = C 1 + 1 C 2 + 1 [ 13 ] where C1 is the cross-correlation coefficient between the L channel signal and the R channel signal,
Monaural signal allpass filter 302 generates a monaural reverberant signal (M′Rev) using allpass filter parameters and the monaural reconstruction signal (M′) received as input from monaural signal generation section 301, and outputs the monaural reverberant signal (M′Rev) to L channel spatial information recreation section 303 and R channel spatial information recreation section 304. Here, the allpass filter parameters are represented by the transfer function shown in equation 6, similar to the L channel allpass filter 203 and R channel allpass filter 204 of embodiment 1 shown in FIG. 7. L channel spatial information recreation section 303 calculates and outputs an Decoded L channel signal (L″), according to equation 14 below, using the cross-correlation comparison result α received as input from separation section 201, the L channel reconstruction signal (L′) received as input from stereo speech decoding section 202 and the monaural reverberant signal (M′Rev) received as input from monaural signal allpass filter 302.
( Equation ⁢ ⁢ 14 ) L ″ = α ⁢ ⁢ L ′ + ( 1 - α 2 ) ⁢  L ′  2  M Rev ′  2 ⁢ M Rev ′ [ 14 ] In a similar manner, R channel spatial information recreation section 304 calculates and outputs an Decoded R channel signal (R″) according to equation 15 below, using the cross-correlation comparison result α received as input from separation section 201, the R channel reconstruction signal (R′) received as input from stereo speech decoding section 202 and the monaural reverberant signal (M′Rev) received as input from monaural signal allpass filter 302.
( Equation ⁢ ⁢ 15 ) R ″ = α ⁢ ⁢ R ′ - ( 1 - α 2 ) ⁢  R ′  2  M Rev ′  2 ⁢ M Rev ′ [ 15 ] Here, L′ and M′Rev are virtually orthogonal to each other, so that the energy of the Decoded L channel signal (L″) is given by equation 16 below. In a similar fashion, R′ and M′Rev are virtually orthogonal to each other, so that the energy of the Decoded R channel signal (R″) is given equation 17 below.
( Equation ⁢ ⁢ 16 )  L ″  2 = ⁢ α 2 ⁢  L ′  2 + ( 1 - α 2 ) ⁢  L ′  2 + 2 ⁢ ⁢ α ⁢ 1 - α 2 ⁢ L ′ � ⁢  L ′  2  M Rev ′  2 ⁢ M Rev ′ = ⁢  L ′  2 [ 16 ] ( Equation ⁢ ⁢ 17 )  R ″  2 =  R ′ 2  [ 17 ] Furthermore, given the orthogonality between L′ and M′Rev and the orthogonality between R′ and M′Rev, the numerator term of the cross-correlation value C3 between the Decoded L channel signal (L″) and the Decoded R channel signal (R″) is given by equation 18 below. Consequently, from equations 13, 16, 17, 18, as shown in equation 19, the cross-correlation value C3 between the Decoded L channel signal and Decoded R channel signal becomes equal to the cross-correlation coefficient C1 between the original L channel signal and R channel signal. It follows from above that L channel spatial information recreation section 303 and R channel spatial information recreation section 304 calculate decoded signals by utilizing the cross-correlation comparison result αaccording to equations 14 and 15, so that decoded signals of the two channels are acquired in such a way that the cross-correlation value between the two signals becomes equal to the original cross-correlation value.
( Equation ⁢ ⁢ 19 ) C 3 = ∑ n ⁢ L ″ ⁡ ( n ) ⁢ R ″ ⁡ ( n ) ∑ n ⁢ L ″ ⁡ ( n ) 2 ⁢ ∑ n ⁢ R ″ ⁡ ( n ) 2 ⁢ ⁢ = α 2 ⁢ C 2 - ( 1 - α 2 ) ⁢ ⁢ = C 1 [ 19 ] Thus, with the present embodiment, upon generating decoded signals of the L channel and the R channel in the decoding end, a monaural reverberant signal (M′Rev) is used instead of an L channel reverberant signal (L′Rev) and R channel reverberant signal (R′Rev), so that it is possible to recreate the spatial information contained in the original stereo signals and improve the spatial images of the stereo speech signals.
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