Coded data generation or conversion – Digital code to digital code converters
Reexamination Certificate
2001-12-12
2003-09-02
Jeanpierre, Peguy (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
C341S067000
Reexamination Certificate
active
06614365
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application(s) No(s). P2000-380642 filed Dec. 14, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coding device and method, a decoding device and method, and a recording medium therefor. More particularly, the present invention relates to a coding device and method and a decoding device and method, which are capable of coding or decoding an audio signal at a low bit rate, and a recording medium therefor.
2. Description of the Related Art
In recent years, a so-called “perception audio coder (decoder)” has been developed. In a conventional CD-ROM (Compact Disk-Read Only Memory), transmission and storage of high-quality audio signals are possible at a bit rate which is approximately one twelfth the bit rate in common use.
Such a coder codes an audio signal by using a waveform portion, which is contained in the audio signal, which cannot be listened to due to the limitation of the auditory system of human beings. With regard to a stereo audio signal, for example, a coder using MS stereo coding (intermediate-portion/side-portion stereo coding) and a coder using IS stereo coding (intensity stereo coding) are known.
FIG. 1
is a block diagram showing an example of the construction of a conventional audio signal transmission system using MS stereo coding.
A left signal L and a right signal R which form a stereo audio signal is input to a computation section
1
. These signals are added by an adder
1
-
1
, and the resulting signal is output to a multiplier
1
-
2
. Meanwhile, a difference signal of those signals is generated in a subtracter
1
-
3
, and the resulting signal is output to a multiplier
1
-
4
. In the multipliers
1
-
2
and
1
-
4
, the outputs of the adder
1
-
1
and the subtracter
1
-
3
are multiplied by a coefficient x, and a sum signal M and a difference signal S are generated. These signals are coded by a coding section
2
, and are output to recording media or a transmission line
3
formed of a network, etc.
A decoding section
4
performs a decoding process on an input code sequence in order to generate a sum signal M′ and a difference signal S′. The sum signal M′ and the difference signal S′ are added by an adder
5
-
1
, and are multiplied by a coefficient y in a multiplier
5
-
2
, and the resulting signal is output as a left signal L′. Also, the sum signal M′ and the difference signal S′ are subtracted by a subtracter
5
-
3
, and the resulting signal is multiplied by a coefficient y in a multiplier
5
-
4
and is output as a right signal R′. For example, the coefficient x is set to 0.5, and the coefficient y is set to 1.0.
A sum signal exerts more influence on the sense of hearing of a human being than a difference signal. In the manner described above, by generating a sum signal M and a difference signal S and by assigning a larger amount of data (the number of bits) to the sum signal M, coding can be performed with higher efficiency than when the signals are coded (dual decoding) individually. MS stereo coding is effective for signals of lower frequency bands.
FIG. 2
is a block diagram showing an example of the construction of a conventional audio signal transmission system using IS stereo coding.
The left signal L and the right signal R which are input to a computation section
11
, are added by an adder
11
-
1
, and an intensity signal I determined by a correlation of those signals is generated. Also, a left power signal P
1
(a scaling signal in which the energy content is described) indicating the power of the left signal L and a right power signal Pr (a scaling signal in which the contents of energy are described) indicating the power of the right signal R are generated in the computation section
11
. The intensity signal I, the left power signal Pl, and the right power signal Pr are input to a coding section
12
, where the signals are coded, and thereafter, the signals are output to a transmission line
13
.
A decoding section
14
decodes the input signals, and outputs the obtained intensity signal I′, left power signal Pl′, and right power signal Pr′ to a computation section
15
. In the computation section
15
, a multiplier
15
-
1
regenerates a left signal L′ in accordance with the intensity signal I′ and the left power signal Pl′ and outputs them externally, and a multiplier
15
-
2
regenerates a right signal R′ in accordance with the intensity signal I′ and the right power signal Pr′ and outputs them externally.
As a result of performing coding by using IS stereo coding, the characteristics such that the position detection performance based on the time difference of the hearing of a human being is lower for a signal in higher-frequency domains can be used. For example, coding can be performed at a data rate approximately one half that in a case where left and right signals are coded independently.
For MS stereo coding and IS stereo coding, equivalent advantages are not obtained with respect to all the input signals. For example, MS stereo coding is an effective means only for the case where the energy of the difference signal S becomes smaller than the energy of the sum signal M. Otherwise, when the left signal L′ and the right signal R′ are regenerated from the sum signal M′ and the difference signal S′, quantization noise which occurs due to coding or decoding (quantization/inverse quantization) causes interference, and noise which can be heard clearly in the sense of hearing may be produced.
Furthermore, in IS coding, when the high-frequency components of a stereo signal are synthesized, and there is not a high correlation between a spectrum SPm which is obtained by converting the components from the time domain to the frequency domain and the envelope shapes of the original power spectra Pl and Pr, for example, when the left signal L is a signal of a trumpet and the right signal R is a signal of cymbals, the positional relationship between the respective sound sources (musical instruments) cannot be maintained, and noise which can be heard clearly may occur in the sense of hearing.
Therefore, a coding device has been conceived in which, as shown in
FIGS. 3
,
4
, and
5
, dual coding in which left and right signals are each coded independently, and MS or IS stereo coding are combined, and a coding method is selected as appropriate in accordance with an input signal.
FIG. 3
is a block diagram showing an example of the construction of a prior coding device for coding an input signal in the time domain.
A filter bank
31
-
1
divides an input left signal L(t) into signals L
n
(t), L
n−1
(t), . . . , L
1
(t) (n is the number of divided bands) of predetermined frequency bands, and outputs each signal to a corresponding dual coding section
32
and a corresponding MS/IS coding section
33
. In
FIG. 3
, although only the dual coding section
32
and the MS/IS coding section
33
for processing the signal L
n
(t) are shown, coding sections corresponding to signals L
n−1
(t), L
n−2
(t), . . . , L
1
(t) are provided in a similar manner.
Similarly to the filter bank
31
-
1
, a filter bank
31
-
2
also divides a right signal R
n
(t) into signals R
n
(t), R
n−1
(t), . . . , R
1
(t) of predetermined frequency bands, and outputs each signal to the corresponding dual coding section
32
and the corresponding MS/IS coding section
33
. In the following, when the filter bank
31
-
1
and the filter bank
31
-
2
need not be identified individually, these are referred to collectively as a filter bank
31
. The same applies to the other devices.
The dual coding section
32
codes an input signal by a dual coding method (the left signal L
n
(t) and the right signal R
n
(t) are each coded independently), and outputs the obtained data to a switch
35
. Furthermore, the dual coding secti
Suzuki Shiro
Toyama Keisuke
Tsuji Minoru
Jeanpierre Peguy
Lauture Joseph
Sonnenschein Nath & Rosenthal
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