Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
2000-09-28
2004-03-23
Abebe, Daniel (Department: 2655)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704SE21020
Reexamination Certificate
active
06711538
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information processing apparatus and method, and to a recording medium therefor. More particularly, the present invention relates to an information processing apparatus and method capable of improving the accuracy of an excitation source in the band spreading of a speech signal, obtaining a wide-band signal having no gaps, and reducing the amount of computation thereof, and to a recording medium therefor.
2. Description of the Related Art
Speech signal transmission technology is becoming prevalent. Speech signal transmission technology is applied to portable telephones, wired telephones, voice recorders, etc. Conventionally, a narrow-band signal of 300 Hz to 3400 Hz is used for transmitting and receiving this speech signal. However, since the frequency band is narrow, there is a problem in that the sound quality is poor. Therefore, in order to overcome this problem, a technique has been developed in which a narrow-band signal is used at the transmission side or in a transmission line, and the receiving side performs a band-spreading process on the received narrow-band signal so that the signal is converted into a wide-band signal.
FIG. 1
is a block diagram showing the construction of a conventional band-spreading apparatus for converting a narrow-band speech signal into a wide-band speech signal.
An &agr; band-widening section
1
causes a prediction coefficient &agr;
N
representing a narrow-band spectrum envelope of a narrow-band speech signal snd
N
to represent a wider band, and outputs it as a prediction coefficient &agr;
W
representing a wide-band spectrum envelope to a wide-band LPC (Linear Predictive Code) combining section
4
. The details of this method of determining the prediction coefficient &agr;
W
from the prediction coefficient &agr;
N
is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-126098.
An adder
2
adds together an adaptive signal (signal containing pitch components) exc
PN
and a noise signal exc
NN
corresponding to the narrow-band speech signal snd
N
, and outputs the sum, as an excitation source exc
N
for a narrow-band speech signal, to an exc band-widening section
3
. The adaptive signal exc
PN
and the noise signal exc
NN
correspond to an output from an adaptive code book and an output from a noise code book, respectively, when a coding apparatus employing a CELP (Code Excited Linear Prediction) method is used for each of them.
The exc band-widening section
3
performs band-widening on the excitation source exc
N
for the input narrow-band speech signal, converts it into an excitation source exc
W
for wide-band speech signal, and outputs it to the wide-band LPC combining section
4
. Specifically, based on the characteristics that the excitation source is almost white noise, aliasing is generated by inserting a zero value between adjacent samples, and the excitation source exc
W
for a wide-band speech signal is generated. The details of this method of determining the excitation source exc
W
for a wide-band speech signal from the excitation source exc
N
for a narrow-band speech signal are also disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-126098 described above.
The wide-band LPC combining section
4
filter-synthesizes the excitation source exc
W
input from the exc band-widening section
3
by using the prediction coefficient &agr;
W
input from the &agr; band-widening section
1
as a filtering coefficient, converts it into a first wide-band speech signal, and outputs it to a band suppression section
5
.
The band suppression section
5
suppresses only the frequency band contained in the narrow-band speech signal within the input first wide-band speech signal, generates a second wide-band speech signal, and outputs it to an adder
7
. That is, since distortion is contained in the first wide-band speech signal, the frequency band of the narrow-band speech signal is replaced with a narrow-band speech signal input from an oversampling apparatus
6
. As a result, distortion of an amount corresponding to the frequency band contained in the original narrow-band speech signal is reduced.
The oversampling apparatus
6
oversamples the input narrow-band speech signal snd
N
at the sampling frequency of the wide-band speech signal, causes the sampling frequency to coincide with the sampling frequency of the wide-band speech signal, and outputs it to the adder
7
.
The adder
7
adds together the second wide-band speech signal input from the band suppression section
5
and the signal input from the oversampling apparatus
6
, thereby generating a final wide-band speech signal snd
W
, and outputting this signal.
Not all of the prediction coefficient &agr;
N
, the adaptive signal exc
PN
, the noise signal exc
NN
, and the narrow-band speech signal snd
N
are independent. The prediction coefficient &agr;
N
can be determined by performing linear prediction analysis on the narrow-band speech signal snd
N
, and the adaptive signal exc
PN
and the noise signal exc
NN
can be determined by performing pitch analysis thereon. The noise signal exc
NN
is a long-term predictive residual, and the sum of the adaptive signal exc
PN
and the noise signal exc
NN
becomes a linear predictive residual. Furthermore, the narrow-band speech signal snd
N
can be determined by performing filter synthesis on the basis of the prediction coefficient &agr;
N
, and the sum of the adaptive signal exc
PN
and the noise signal exc
NN
. In addition, the prediction coefficient &agr;
N
, the adaptive signal exc
PN
, and the noise signal exc
NN
can also be determined by preprocessing the narrow-band speech signal snd
N
and can also be determined on the basis of a quantized signal.
Next, a description is given of the operation when a conventional band-spreading apparatus converts the input narrow-band speech signal snd
N
into a wide-band speech signal snd
W
.
The a band-widening section
1
causes the prediction coefficient &agr;
N
of the input narrow-band speech signal to represent a wider band, and outputs it as a prediction coefficient &agr;
W
of the wide-band speech signal to the wide-band LPC combining section
4
.
The adder
2
adds together the input adaptive signal exc
PN
and the noise signal exc
NN
, and outputs an excitation source exc
N
for the narrow-band speech signal to the exc band-widening section
3
. The exc band-widening section
3
performs band-widening on the excitation source exc
N
for the input narrow-band speech signal, and outputs it as an excitation source exc
W
for the wide-band speech signal to the wide-band LPC combining section
4
.
The wide-band LPC combining section
4
performs a filtering process on the excitation source exc
W
for the wide-band speech signal on the basis of the prediction coefficient &agr;
W
of the input wide-band speech signal, generates a first wide-band speech signal, and outputs it to the band suppression section
5
. The band suppression section
5
suppresses the frequency band contained in the narrow-band speech signal within the input first wide-band speech signal, generates a second wide-band speech signal, and outputs it to the adder
7
.
The oversampling apparatus
6
oversamples the input narrow-band speech signal snd
N
at the sampling frequency of the wide-band speech signal, and outputs it to the adder
7
.
The adder
7
adds together the second wide-band speech signal input from the band suppression section
5
and the oversampled signal input from the oversampling apparatus
6
, generates a final wide-band speech signal snd
W
, and outputs it.
The band suppression section
5
may be a high-pass filter which, instead of strictly suppressing only the frequency band of the narrow-band speech signal, for example, suppresses only a low-frequency band, and also, the band suppression section
5
may multiply a gain factor or may perform a filtering process.
However, in the above-described method, originally, since the excitation source formed
Nishiguchi Masayuki
Omori Shiro
Abebe Daniel
Maioli Jay H.
Sony Corporation
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