Note: Descriptions are shown in the official language in which they were submitted.
CA 02355194 2001-07-31
WIDEBAND SPEECH DECODER
BACKGROUND OF THE INVENTION
This application is a division of Canadian Patent
Application Serial No. 2,208,384, filed on June 20, 1997. The
claims of the parent application are directed to a Wideband
Speech Coder. However, in order to assist the reader to readily
understand the overall invention including all features which
are inextricably bound up in the one and the same inventive
concept, the teachings of those features and the broad objects
relating thereto are all retained in the present description.
Aspects of the overall invention relate to a wideband
speech and audio signal coding/decoding system and, more
particularly, to a band division coding/decoding system.
Well-known speech coding/decoding systems are disclosed
in, for instance, R.D. Jacovo et al, "Some Experiments of 7-kHz
Audio Coding at 16 kbit/s", IEEE, 1989, pp. 192-195
(hereinafter referred to as Literature 1), and M. Yong,
"Subband Vector Excitation Coding with Adaptive Bit-
Allocation", IEEE ICASSP 1989, S14.3, pp. 743-746 (hereinafter
referred to as Literature 2).
In the wideband speech coding/decoding systems, in coding
the band of a band-divided input speech signal is divided, and
the input speech signal is coded for each subband. The input
signal is modeled using line prediction(LPC)coefficients as an
envelope of the spectral form and an excitation signal of a
filter constituted by the LPC coefficients, and each subband
input speech signal is coded using model parameters of the LPC
coefficients and the excitation signal.
In the decoding, each subband speech signal is decoded
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using the each subband decoded LPC coefficients and excitation
signal, and the speech signal is synthesized using the last
decoded subband
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signals.
A prior art wideband speech coding/decoding
system will now be described with reference to Figs.
14 and 15.
First, the operation of the coding part of the
system will be described with reference to Fig. 14.
A band divider 20 band-divides a speech signal
input from an input terminal 10 (i.e., an input
speech signal). LPC analyzers 22 and 24 LPC-analyze
each subband.input speech signal, and LPC coders 13
and 14 quantize each LPC coefficients thus obtained.
Coders 26 and 28 quantize the excitation signal
using each subband input speech signal and quantized
LPC coefficients. Codes that are obtained as a
result of the quantization in the LPC coders 13 and
14 and coders 26 and 28 are outputted to a
multiplexes 30. The multiplexes 30 modulates the
input codes, and outputs the modulated signal from
an output terminal 32.
-As means of the band division in the band
divider 20, a quadrature mirror filter (QMF), for
instance, is well-known in the art. The QMF divides
the band with a ratio of 2:1, and it is used a
plurality of times to divide the input speech signal
, into a plurality of subbands. The QMF is detailed
in, for instance, IEEE Proceeding of ICASSP, pp.
191-195, 1977 (Literature 3).
As means of the LPC analysis in the LPC
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analyzers 22 and 24, autocorrelation analysis and
covariance analysis are well known in the art. The
LPC analysis in LPC analyzers 22 and 24 is detailed
in, for instance, L. R. Labiner and R. W. Schafer,
"Digital Processing of Speech Signal", Section S.1,
pp. 398-404, Prentice-Hall Signal Processing Series
(Literature 4), and is not described here.
As a method of the LPC coefficient quantization
in the LPC coders 13 and 14, it is well known to
convert the LPC coefficients into a line spectrum
pair (LSP) before vector quantization. The vector
quantization of the LSP coefficients is detailed in,
for instance, IEEE Transactions of Speech and Audio
Processing, Vol. 1, No., January 1993 (Literature
5), and is not described here.
As a method of the excitation signal coding in
the coders 26 and 28, it is well known one in a
Code-Excited Linear Prediction (CELP) system. In
the excitation signal coding method in the CELP
system, a pitch cycle component of the excitation
signal of the input speech signal is represented by
a pitch prediction filter, and the filter
coefficients thereof and the pitch are quantized.
The pitch prediction residue is also vector-
quantized. As the distance in the vector
quantization is used the error power between the
input speech signal and the reproduced speech
signal, which is calculated using the quantized LPC
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coefficients obtained through analysis of the input
speech signal. In order zo ~uml~~~ ~~.~ --.---.__
quality in the perceptual aspect, the above distance
is set by weighting the above error power with the
use of a perceptual weighting function which is
constituted by the LPC coefficients. The CELP
system is detailed in IEEE Proceedings of ICASSP-85,
pp. 937-940, 1985 (Literature 6) and ITU-T
Recommendation, 723, International Telecommunication
Union Telecommunication Standardization Sector
(ITU-T) COM15-153-E, July (Literature 7).
The operation of the decoding part of the
system will now be described with reference to Fig.
15.
A demultiplexer -- -36 demodulates the modulation
signal that is input from an input terminal 34 to
generates codes. LPC decoders 38 and 41 receive the
codes from the demultiplexer 36, and obtain each
subband LPC coefficients by decoding each code.
Decoders 48 and 50 receives the codes from the
demultiplexer 36, and obtain each subband excitation
signal by the decoding. Reproducing circuits 52 and
54 reproduce subband speech signals by using the
excitation signals obtained by the decoding in the
decoders 48 and 50 and the LPC signals obtained by
the decoding in the LPC decoders 38 and 41. A
fullband synthesizer 56 synthesizes the fullband
speech signal by using the subband speech signals
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reproduced from the reproducing circuits 52 and 54,
and outputs the synthesized signal from an output
terminal 56. The operation of the fullband
synthesizer 56 is as described in Literature.3 noted
above.
As shown above, in the prior art wideband
speech coder/decoder does coefficient coding for
each subband. Therefore, the quantized coefficients
contain band division filter characteristics which
need not be transmitted. This means that the prior
art speech coding/decoding system quantizes
unnecessary information when quantizing the
analytically obtained coefficients, resulting in
deterioration of its quantization performance.
In addition, the prior art wideband speech
coding/decoding system executes LPC quantization
after LPC analysis for each subband. Therefore, the
analysis order should be determined before the LPC
guantization. .This means that parameters that are
necessary for the analysis for each subband should
be determined before quantizing the coefficients
obtained as a result of the analysis.
Moreover, in the prior art coding/decoding
system the band division in a band division filter
may result in the generation of a delay due to the
division. For example, in the case of band division
into two subbands using a QMF band division filter
which generates a D sample delay, extension of the
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analysis window by L samples to the future results
in a (L+D) sample delay. Therefore, if the delay is
allowed by only L samples, the length of window
extension to the future should be set to (L - D)
samples. This limitation may lead to a too short
analysis window or absence of the
analysis window center at a proper position. In
such a case, the excitation signal coding
characteristic is deteriorated. In other words, the
scope of the.iaindow for cutting out signal to be
used for the analysis is limited by the band-pass
f i lter .
SUMMARY OF THE INVENTION
An object of the present invention is therefore
to provide a wideband speech coding/decoding system,
which does not transmit unnecessary information and
is free from quantization performance deterioration.
Another object of the present invention is to
provide a wideband coder/decoder, which does not
determine any parameter for the coefficient analysis
for each subband before the coefficient
quantization.
A further object of the present invention is to
provide a wideband speech coder/decoder, in which
the analysis window is not limited by any band-pass
f i lter .
According to a first aspect of the present invention,
which is claimed in the parent application Serial No.
2,208,384, there is provided a wideband speech
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coding system comprising means for quantizing
coefficients obtained from an input speech signal
through analysis thereof, means for obtaining an
impulse response of the quantized coefficients,
means for dividing the frequency band of the impulse
response and dividing the band of the input speech
signal by calculating each subband coefficients
through analysis of each subband impulse response,
and means for quantizing an excitation signal of the
input speech signal by using the input speech signal and
coefficients of each subband and outputting a
modulation signal obtained by modulating
quantized codes of the coefficients and excitation
signal of each subband.
According to a second aspect of the present
invention, there is provided a wideband speech
decoding system comprising means for determining
coefficients by decoding a code obtained through
demodulation of an input modulation signal and
calculating an impulse response of the coefficients,
means for dividing the band of the impulse signal
and calculating each coefficients by analyzing each
subband impulse response, and means for obtaining
each subband excitation signal by decoding each
subband code, reproducing each subband speech signal
by using the calculated coefficients and decoded
excitation signal of each subband, and synthesizing
the fullband speech signal from the subband speech
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signals.
According to a third aspect of the present invention,
which is claimed in the parent application Serial No.
2,208,384, there is provided a wideband speech
coding system comprising means for quantizing
coefficients obtained from an input speech signal
through analysis thereof, means for dividing the
band of the coefficients obtained through the
quantization and quantizing an excitation signal of
the input speech signal by using each subband speech
signal obtained from the input speech signal and
each subband coefficients, and means for outputting
a modulation signal obtained by modulating the code
obtained by quantizing the coefficients and the code
obtained by each subband excitation signal.
According to a fourth aspect of the present
invention, there is provided a wideband speech
decoding system comprising means for obtaining
coefficients by decoding a code obtained by an input
modulation signal, dividing the band of the .
coefficients and obtaining each subband excitation
signal by decoding each subband code, and means for
reproducing each subband speech signal by using each
subband coefficients and excitation signal obtained
by the decoding and synthesizing the fullband speech
signal from the subband speech signals.
According to a fifth aspect of the present invention,
which is claimed in the parent application Serial No.
2,208,384, there is provided a wideband speech coding system
comprising means for quantizing
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coefficients obtained from an input speech signal
through analysis thereof, means for calculating an
impulse response of the coefficients obtained by the
quantization, dividing the band of the input speech
signal by dividing the frequency band of the impulse
response and quantizing an excitation signal of the
input speech signal and impulse response of each
subband, and means for outputting a modulation
signal obtained by modulating the code obtained by
quantizing the coefficients and the code obtained by
quantizing each subband excitation signal.
According to a sixth aspect of the present
invention, there is provided a wideband speech
decoding system comprising means for determining
coefficients by decoding a code obtained by
demodulating an input modulation signal, calculating
an impulse response of the coefficients, dividing
the band of the impulse response, and means for
obtaining each subband excitation signal by decoding ..
the code in each subband, and reproducing each
subband speech signal by using each subband impulse
response and the excitation signal obtained by the
decoding and synthesizing the fullband speech signal
from the subband speech signals.
According to a seventh aspect of the present invention,
which is.claimed in the parent application Serial No.
2,208,384, there is provided a wideband speech coding system
comprising means for quantizing coefficients obtained from an
input speech signal
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through analysis thereof, means for converting the
quantized coefficients into frequency band
coefficients, dividing the band of the frequency
band coefficients, dividing the band of the input
speech signal by converting each subband frequency
band coefficients into each subband second
coefficients and quantizing an excitation signal of
the input speech signal by using the speech signal
and second coefficients of each subband, and means
for outputting a modulation signal obtained by
modulating the code obtained by quantizing the
coefficients and the code obtained by quantizing
each subband excitation signal.
According to an eighth aspect of the present
invention, there is provided a wideband speech
decoder comprising means for determining
coefficients by decoding a code obtained by
demodulating an input modulation signal, converting
the coefficients into frequency band coefficients,
dividing the band of the frequency band
coefficients, converting each subband frequency band
coefficients into each subband second coefficients,
and obtaining each subband excitation signal by
decoding each subband code, and means for
reproducing each subband speech signal by using the
second coefficients and the excitation signal
obtained by the decoding in each subband.
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According to a ninth aspect of the present invention,
which is claimed in the parent application Serial No.
2,208,384, there is provided a wideband speech
coding system comprising means for converting
coefficients obtained from . input speech signals
through analysis thereof into frequency band
coefficients and quantizing the frequency band
coefficients, means for dividing the band of the
quantized frequency band coefficients into subband
frequency band coefficients, dividing the frequency
of the input .speech signalsby converting each
subband frequency band coefficients into second
coefficients and quantizing an excitation signal of
the input speech signal by using the speech signals
and second coefficients of each subband, and means
for outputting a modulation signal obtained by
modulating the codes obtained by quantizing the
coefficients and each subband excitation signal.
According to a tenth aspect of the present
invention, there is provided a wideband speech
decoding system comprising means for determining a
frequency band coefficients by decoding a code
obtained by demodulating an input modulation signal,
means for dividing the frequency band coefficients
into subband frequency band coefficients, converting
each thereof into second coefficients and obtaining
each subband excitation signal by decoding the code
in each subband, and means for reproducing each
subband speech signal by using the second
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coefficients and the excitation signal obtained by the decoding
of each subband and synthesizing the fullband speech signal
from the subband speech signals.
According to an eleventh aspect of the present invention,
which is claimed in the parent application Serial No.
2,208,384, there is provided a wideband speech coding system
comprising means for dividing the band of an input speech
signal and determining frequency band coefficients by
demodulating coefficients obtained from each subband speech
signal through analysis thereof, means for obtaining fullband
frequency band coefficients by combining the subband frequency
band coefficients and quantizing the fullband frequency band
coefficients, means for dividing the band of the guantized
frequency band coefficients into subbands and into subband
quantized frequency band coefficients and converting each
thereof into second coefficients, and means for quantizing the
excitation signal of each subband speech signal by using each
subband second coefficients and outputting a modulation signal
obtained by demodulating the codes obtained by quantizing the
frequency band coefficients and excitation signal of each
subband:
According to a twelfth aspect of the present invention,
there is provided a wideband speech decoding system, comprising
a demultiplexing unit configured to receive a modulated signal
and to demodulate the modulated signal and to output a first
signal as a result; an LPC decoder unit communicatively
connected to the demultiplexing unit and configured to perform
LPC analysis so as to obtain LPC coefficients from the first
signal; an impulse response unit communicatively connected to
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the LPC decoder unit and configured to calculate an impulse
response of the first signal based on the LPC coefficients; a
band divider communicatively connected to the impulse response
unit and configured to divide the impulse response of the first
signal into first through nth frequency bands, n being an
integer greater than one; first through nth LPC analyzer units
communicatively connected to receive a corresponding one of the
first through nth frequency bands of the first signal output
from the band divider, the first through nth LPC analyzer units
configured to calculate first through nth subband LPC
coefficients respectively; first through nth decoder units
configured to receive and decode the modulated signal and to
obtain first through nth excitation signals for the first
through nth frequency bands, respectively: first through nth
reproducing units communicatively connected to a corresponding
one of the first through nth decoder units and a corresponding
one of the first through nth LPC analyzer units, the first
through nth reproducing units configured to reproduce a subband
speech signal in the first through nth frequency bands,
respectively, based on a corresponding one of the first through
nth excitation signals and a corresponding one of the first
through nth subband LPC coefficients; and a fullband
synthesizing unit communicatively connected to the first
through nth reproducing units and configured to create a
fullband signal based on the corresponding subband speech
signals in the first through nth frequency bands respectively
output by the first through nth reproducing units.
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According to thirteenth aspect of the present invention,
there is provided a wideband speech decoding system,
comprising: a demultiplexing unit configured to receive a
modulated signal and to demodulate the modulated signal and to
output a first signal as a result; an LPC decoder unit
communicatively connected to the demultiplexing unit and
configured to perform LPC analysis so as to obtain LPC
coefficients from the first signal; a band divider
communicatively connected to the LPC decoder unit and
configured to divide the first signal into first through nth
frequency bands, n being an integer greater than one, the band
divider further configured to calculate first subband LPC
coefficients for the respective first through nth frequency
bands; first through nth decoder units configured to receive
the modulated signal and to obtain first through nth excitation
signals for the first through nth frequency bands,
respectively; first through nth reproducing units
communicatively connected to receive the first. subband LPC
coefficients for a corresponding one of the first through nth
frequency bands of the first signal output from the band
divider, and communicatively connected to receive a
corresponding one of the first through nth excitation signals
respectively output from the first through nth decoder units,
the first through nth reproducing units configured to
demodulate a subband speech signal for each of the first
through nth frequency bands as a result; and a fullband
synthesizing unit communicatively connected to the first
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through nth reproducing units and configured to create a
fullband signal based on the corresponding subband speech
signals in the first through nth frequency bands respectively
output by the first through nth reproducing units.
According to a fourteenth aspect of the present invention,
there is provided a wideband speech decoding system,
comprising:
a demultiplexing unit configured to receive a modulated signal
and to demodulate the modulated signal and to output a first
signal as a result; an LPC decoder unit communicatively
connected to the demultiplexing unit and configured to perform
LPC analysis so as to obtain LPC coefficients from the first
signal; an impulse response unit communicatively connected to
the LPC decoder unit and configured to calculate an impulse
response of the first signal based on the LPC coefficients; a
band divider communicatively connected to the impulse response
unit and configured to divide the input response of the first
signal into first through nth frequency bands, n being an
integer greater than ones first through nth decoder units
configured to receive the modulated signal and to obtain first
through nth excitation signals for first through nth frequency
bands, respectively; first through nth reproducing units
communicatively connected to receive the first subband LPC
coefficients for a corresponding one of the first through nth
frequency bands of the first signal output from the band
divider, and communicatively connected to receive a
corresponding one of the first through nth excitation signals
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respectively output from the first through nth decoder units,
the first through nth reproducing units configured to
demodulate a subband speech signal for each of the first
through nth frequency bands as a result; and a fullband
synthesizing unit communicatively connected to the first
through nth reproducing units and configured to create a
fullband signal based on the corresponding subband speech
signals in the first through nth frequency bands respectively
output by the first through nth reproducing units.
According to a fifteenth aspect of the present invention,
there is a provided a wideband speech decoding system,
comprising:
a demultiplexing unit configured to receive a modulated signal
and to demodulate the modulated signal and to output a first
signal as a result; an LPC decoder unit communicatively
connected to the demultiplexing unit and configured to perform
LPC analysis so as to obtain LPC coefficients from the first
signal; an LPC-LSP converter communicatively connected to the
LPC decoder unit and configured to convert the LPC coefficients
into LSP coefficients;
an LSP band divider communicatively connected to the LPC-LSP
converter and configured to divide the LSP coefficients into
subband LSP coefficients for first through nth frequency bands,
n being an integer greater than one;first through nth LSP-LPC
converters communicatively connected to receive the subband LSP
coefficients output from the band divider for a corresponding
one of the first through nth frequency bands, and to calculate
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first through nth subband LPC coefficients, respectively; first
through nth decoder units configured to receive and decode the
modulated signal and to obtain first through nth excitation
signals for the first through nth frequency bands,
respectively; first through nth reproducing units
communicatively connected to a corresponding one of the first
through nth decoder units and a corresponding one of the first
through nth LSP-LPC converters, the first through nth
reproducing units configured to reproduce a subband speech
signal in the first through nth frequency bands, respectively,
based on a corresponding one of the first through nth
excitation signals and a corresponding one of the first through
nth subband LPG coefficients; and a fullband synthesizing unit
communicatively connected to the first through nth reproducing
units and configured to create a fullband signal based on the
corresponding subband speech signals in the first through nth
frequency bands respectively output by the first through nth
reproducing units.
According to a sixteenth aspect of the present invention,
there is provided a wideband speech decoding system,
comprising:
a demultiplexing unit configured to receive a modulated signal
and to demodulate the modulated signal and to output a first
signal as a result; an LPC decoder unit communicatively
connected to the demultiplexing unit and configured to perform
LPC analysis so as to obtain LPC coefficients from the first
signal; an LSP band divider communicatively connected to the
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LPC decoder unit and configured to divide the LSP coefficients
into subband LSP coefficients for first through nth frequency
bands, n being an integer greater than one; first through nth
LSP-LPC converters communicatively connected to receive the
subband LSP coefficients output from the band divider for a
corresponding one of the first through nth frequency bands, and
to calculate first through nth subband LPC coefficients,
respectively; first through nth decoder units configured to
receive and decode the modulated signal and to obtain first
through nth excitation signals for the first through nth
frequency bands, respectively; first through nth reproducing
units communicatively connected to a corresponding one of the
first through nth decoder units and a corresponding one of the
first through nth LSP-LPC converters, the first through nth
reproducing units configured to reproduce a subband speech
signal in the first through nth frequency bands, respectively,
. based on a corresponding one of the first through nth
excitation signals and a corresponding one of the first through
nth subband LPC coefficients; and a fullband synthesizing unit
communicatively connected to the first through nth reproducing
units and configured to create a fullband signal based on the
corresponding subband speech signals in the first through nth
frequency bands respectively output by the first through nth
reproducing units.
As shown above, according to the present invention the
coefficients which are obtained for the input fullband speech
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signal are quantized for the full band. It is thus possible to
obtain
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quantized coefficients, which are free form band
division filter characteristics.
In addition, by permitting analysis for each
subband once again after conversion of the fullband
quantized coefficients into impulse responses, the
coefficient analysis parameters may be varied after
the coefficient quantization.
Moreover, by making the fullband analysis
before the band division, the analysis window is not
affected by any delay due to the band division.
Other objects and features will be clarified
from the following description with reference to
attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows the coding part of a first
embodiment of the present invention;
Fig. 2 shows the decoding part of the first
embodiment;
Fig. 3 shows the coding part of a second
embodiment;
Fig. 4 shows the decoding part of the second
embodiment
Fig. 5 shows the coding part of a third
embodiment;
Fig. 6 shows the decoding part of the third
embodiment;
Fig. 7 shows the coding part of a fourth
embodiment;.
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Fig. 8 shows the decoding part of the fourth
embodiment;
Fig. 9 shows the coding part of a fifth
embodiment;
Fig. 10 shows the decoding part of the fifth
embodiment;
Fig. 11 shows the coding part of a sixth
embodiment;
Fig. 12 shows the decoding part of a sixth
embodiment;
Fig. 13 shows the decoding part of a seventh
embodiment; and
Figs 14 and 15 show block diagrams of a prior
art wideband speech coding/decoding system.
PREFERRED EMBODIMENTS OF THE INVENTION
Fig. 1 shows the coding part of a first
embodiment of the present invention.
An LPC analyzer 12 calculates the LPC
coefficients of a speech signal input from an input
terminal 10 through LPC analysis of the signal. An
LPC coder 14 codes the LPC coefficients to generate
coded LPC coefficients. An impulse response circuit
16 calculates the impulse response of the signal by
using the coded LPC coefficients. A band divider 18
divides the band of the impulse response. LPC
analyzers 22 and 24 calculate the subband LPC
coefficients of each subband.
A band divider 20 divides the band of the
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speech signal input from the input terminal 10 to
produce subband speech signals (i.e., subband
signals). Coders 26 and 28 code the excitation
signal using the subband LPC coefficients and the
subband signal for each subband. A multiplexer 30
outputs the codes thus obtained as a modulation
signal from an output terminal 32.
The impulse response circuit l6 constitutes a
auto-regressive filter H(z) given by equation (1)
using the quantized LPC coefficients a(i) received
from the LPC coder 14.
H(z) - 1/(1+Eiao a(i)z) (1)
where P is the degree of the LPC analysis, and
outputs an output signal when signal
[1,0,0,0,0,0,...,0] is input..
A band divider 18 divides the band of the
received impulse response with the QMF band division
filter noted above.
Fig. 2 shows the decoding part of the first
embodiment. A demultiplexer 36 obtains the code by
demodulating the modulation signal input from an
input terminal 34. An LPC decoder 38 obtains the
LPC coefficients by decoding the code. An impulse
response circuit 16 calculates the impulse response
from the LPC coefficients. A band divider 18
divides the band of the impulse response. LPC
analyzers 22 and 24 calculate the subband LPC
coefficients for each subband. Decoders 48 and 50
CA 02355194 2001-07-31
obtain the excitation signal of each subband through
the decoding. Reproducing circuits 52 and 54 decode
each subband speech signal by using the LPC
coefficients and excitation signal of each subband.
A fullband synthesizer 56 synthesizes the fullband
decoded speech signal from the subband decoded
speech signals, and outputs this decoded speech
signal to an output terminal 58.
Fig. 3 shows the coding part of a second
embodiment. An LPC analyzer 12 calculates the LPC
coefficients of a speech signal input from an input
terminal 10 through LPC analysis of the signal. An
LPC coder 14 codes the LPC coefficients. A filter
band divider 18 divides the band of coded LPC
coefficients, and calculates the LPC coefficients of
each subband (i.e., subband LPC coefficients).
A band divider 20 divides the band of the
speech signal input from the input terminal 10, and
calculates the LPC coefficients of each subband
(i.e.-, subband LPC coefficients). Coders 26 and 28
code the excitation signal using the subband LPC
coefficients and the subband signal for each
subband. A multiplexer 30 outputs the code thus
obtained as a modulation signal from an output
terminal 32.
The band divider 18 receives a signal
[l,a(0),a(1),...,a(P),0,0,...,0], obtained by
zero-padding to the end of the received LPC
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coefficients and divides the signal with the QMF
band division filter noted above.
The coding part shown in Fig. 3 is different
from the coding part shown in Fig. 1 in the method
of the LPC coefficients band division.
Fig. 4 shows the decoding part of the second
embodiment. A demultiplexer 36 demodulates the code
from the modulation signal input from an input
terminal 34. A band divider 18 divides the band of
the LPC coefficients, and calculates each subband
LPC coefficients. Decoders 48 and 50 obtain each
subband excitation signal through the decoding, and
reproducing circuits 52 and 54 demodulate each
subband speech signal by using the LPC coefficients
and excitation signal of each subband. A band
synthesizer 56 synthesizes the fullband decoded
speech signal from the subband decoded speech
signals, and outputs the decoded speech signal from
an output terminal 58.
-The decoding part shown in Fig. 4 is different
from the decoding part shown in Fig. 2 in the LPC
coefficient band division method.
Fig. 5 shows the coding part of a third
embodiment. An LPC analyzer 12 calculates the LPC
coefficients of a speech signal input from an input
terminal 10 through the LPC analysis of the signal.
An LPC coder.l4 codes the LPC coefficients. An
impulse response circuit 16 calculates the impulse
17
CA 02355194 2001-07-31
response by using the coded LPC coefficients. A
band divider 20 divides the band of the speech
signal input from the input terminal 10 and
generates each subband speech signal. Coders 26 and
28 code each subband excitation signal by using the
impulse response and the input speech signal of each
subband. A multiplexer 30 outputs the codes as a
modulation signal from an output terminal 32.
The coding part shown in Fig. 1 uses, as a
reproducing filter for reproduction, a
auto-regressive filter constituted by the LPC
coefficients, whereas the coding part shown in Fig.
5 uses a moving average filter constituted by the
impulse response.
Fig. 6 shows the decoding part of the third
embodiment. A multiplexer 36 demodulates the code
from the modulation signal input from an input
terminal 34. An LPC decoder 38 obtains the LPC
coefficients by decoding the code. An impulse
response circuit 16 calculates the impulse response
from the LPC coefficients. A band divider 18
divides the band of the impulse response. Decoders
48 and 50 obtain each subband excitation signal
through the decoding. Hepr~uu~l~=s ~~-~-___ -
54 decode each subband speech signal by using the
impulse response and the excitation signal of each
subband. A band synthesizer 56 synthesizes the
fullband speech signal from the subband decoded
18
CA 02355194 2001-07-31
speech signals, and outputs the decoded speech
signal from an output terminal 58.
The decoding part shown in Fig. 2 uses, as a
reproducing filter for reproduction, a
auto-regressive filter constituted by LPC
coefficients, whereas the decoding part shown in
Fig. 6 uses a moving average filter constituted by
impulse response.
Fig. 7 shows the coding part of a fourth
embodiment. An LPC analyzer 12 calculates the LPC
coefficients of a speech signal input from an input
terminal 10 through LPC analysis. An LPC coder l4
codes the LPC coefficients. An LPC-LSP converter 15
converts the LPC coefficients into the LSP
coefficients. An LSP band divider 17 divides the
LSP coefficients into subband LSP coefficients.
LSP-LPC converters 19 and 21 convert each
subband LSP coefficients into the corresponding
subband LPC coefficients. A band divider 20 divides
the band of the speech signal input from the input
terminal 10, and generates each subband speech
signal. Coders 26 and 28 code each subband
excitation signal by using the LPC coefficients and
the input speech signal of each subband. A
multiplexer 30 outputs each code as a modulation
signal from an output terminal 32.
As shown, the LPC-LSP converter 15 and the
LSP-LPC converters 19 and 21 execute the conversion
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CA 02355194 2001-07-31
between the LPC and LSP coefficients. The method of
the conversion is detailed in, for instance, IEEE
Proceedings of CASSP-84, pp. 1.10.1-I.10.4, 1994
(Literature 8).
The LSP band divider 17 classifies LSP
coefficients into pertaining subbands. For example,
in the case where the band division number is 2, the
LSP band divider 15 checks the subbands, to which
LSP coefficients which have frequency-defined values
L(1), L(2), ..., L(P) belong. Where LSP
coefficients L(1) to L(4) and L(5) to L(P) belong to
the first and second subbands, respectively, the LSP
band divider 17 outputs LSP coefficients L(1), ...,
L(4) and L(5), ..., L(P) , respectively.
The coding part shown in Fig. 1 divides the LPC
coefficients through the impulse response as the
method of the filter coefficient band division,
whereas the coding part shown in Fig. 7 effects the
band division through the LSP coefficients.
-Fig. 8 shows the decoding part of the fourth
embodiment. A multiplexer 36 demodulates the code
from the modulation signal input from an input
terminal 34. An LPC decoder 38 obtains the LPC
coefficients by decoding the code. An LPC-LSP
converter 15 converts the LPC coefficients into the
LSP coefficients. An LSP band divider 17 divides
the LSP coefficients into subband LSP coefficients.
LSP-LPC converters 19 and 21 convert each
CA 02355194 2001-07-31
subband LSP coefficients into each subband LPC
coefficients. Decoders 48 and 50 obtain each
subband excitation signal by the decoding.
Reproducing circuits 52 and 54 decode each subband
speech signal by using the LPS coefficients and the
excitation signal of each subband. A band
synthesizer 56 synthesizes the fullbands decoded
speech signal from the subband decoded speech
signals, and outputs the decoded speech signal from
an output terminal 58.
The decoding part shown in Fig. 2 divides the
LPC coefficient band through the LPC coefficients as
the method of the filter coefficient band division,
whereas the decoding part shown in Fig. 8 executes
the band division through the LSP coefficients.
Fig. 9 shows the coding part of a fifth
embodiment. An LPC analyzer 12 calculates the LPC
coefficients of a speech signal input from an input
terminal 10 by making LPC analysis of the signal.
An LPC-LSP converter 15 converts the LPC
coefficients into the LSP coefficients. An LSP
coder 25 codes the LSP coefficients. An LSP band
divider 17 divides the LSP coefficients into subband
LSP coefficients.
LSP-LPC converters 19 and 21 converts each
subband LSP coefficients into each subband LPC
coefficients. A band divider 20 divides the band of
the speech signal input from the input terminal 10
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CA 02355194 2001-07-31
to generate each subband speech signal. Coders 26
and 28 code each subband excitation signal by using
the LPC coefficients and the input speech signal of
each subband. A multiplexes 30 outputs each code as
a modulation signal from an output terminal 32.
The coding part shown in Fig. 7 quantizes the
LPC coefficients, whereas the codes shown in Fig. 9
converts the LPC coefficients into the LSP
coefficients before quantization thereof.
Fig. 10 shows the decoding part of the fifth
embodiment. A demultiplexer 36 obtains the code by
demodulating the modulation signal input from the
input terminal 34. An LSP decoder 39 obtains the.
LSP coefficients by decoding the code. An LSP band
divider 17 divides the LSP coefficients into each
subband LSP coefficients.
LSP-LPC converters 19 and 21 convert each LSP
coefficients into each subband LPC coefficients.
Decoders 48 and 50 decode each subband speech signal
by using the LPC coefficients and the excitation
signal from each subband. A band synthesizer 56
synthesizes the fullband decoded speech signal from
the subband decoded speech signals, and outputs the
decoded speech signal from an output terminal 58.
Fig. 11 shows the coding part of a sixth
embodiment. A band divider 20 divides the band of
an input speech signal input from an input terminal
10. LPC analyzers 22 and 24 calculate the LPC
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CA 02355194 2001-07-31
coefficients of each subband speech signal through
LPC analysis. LPC-LSP converters 11 and 15 convert
each subband LSP coefficients into each subband LSP.
An LSP synthesizer 23 combines the subband LSP
coefficients. An LSP coder 25 codes the resultant
LSP coefficients. An LSP band divider 17 divides
the coded LSP coefficients into subband LSP
coefficients.
LSP-LPC converters 19 and 21 convert each
subband LSP coefficients into each subband LPC
coefficients. Coders 26 and 28 code each subband
excitation signal by.using the LPC coefficients and
the input speech signal of each subband. A
multiplexer 30 outputs each code as a modulation
signal from an output terminal 32.
The LSP synthesizer 23 combines the received
subband LSP coefficients in the order of lower
subbands. For example, where subband coefficients
[L(1),...,L(4)] and [L(5),...,L(P)] are input to it
with a division ratio of 2, the LSP synthesizer 23
outputs an output [L(1),L(2)....,L(P)] as the
resultant LSP coefficients.
The coding parts shown in Figs. 9 and 11 are
different from each other in whether the LPC
analysis is done in the full band or in each
subband.
Fig. 12 shows the decoding part of a sixth
embodiment. A demultiplexer 36 obtains the codes by
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CA 02355194 2001-07-31
decoding the demodulation signals input from an
input terminal 34. An LPC decoder 39 obtains each
subband LPC coefficients by decoding each code.
Decoders 48 and 50 obtain each excitation signal by
decoding each code. A band synthesizer 56
synthesizes the fullband decoded excitation signal
from the subband decoded excitation signals. A
reproducing circuit 52 decodes the fullband speech
signal by using the decoded subband LPC coefficients
and excitation signals, and outputs the decoded
speech signal from an output terminal 58.
Fig. 13 shows the decoding part of a seventh
embodiment. A demultiplexer 36 demodulates the
codes from the demodulation signals input from an
input terminal 34. An LSP decoder 39 obtains each
subband LSP coefficients by obtaining each code. An
LSP-LPC converter 19 converts each LSP coefficients
into each subband LPC coefficients. Decoders 48 and
50 obtain the subband coded excitation signals by
the decoding. A band synthesizer 56 synthesizes the
fullband decoded excitation signal from the subband
decoded excitation signals. A reproducing circuit
52 decodes the fullband speech signal by using the
decoded LPC coefficients and excitation signal, and
outputs the decoded speech signal of the full band
from an output terminal 58.
In the coding part of the above sixth
embodiment, the coder 26 can make perceptual
24
CA 02355194 2001-07-31
weighting giving considerations to the person's
perceptual characteristics by using the
non-quantized LPC coefficients. Again in this case,
like the case of using the quantized LPC
coefficients; it is possible to divide the band of
the quantized LPC coefficients by the agency of the
LSP coefficients or .impulse response and use each
subband quantized LPC coefficients.
While the above embodiment concerned with the
LPC coefficients as coefficients obtained as the
analysis result, the cepstrum coefficients, Parcor
coefficients and impulse response may also be used
likewise.
While the above embodiments used the
demultiplexers and multiplexers, it is possible to
omit the multiplexer and demultiplexer and directly
transmit codes.
As has been described in the foregoing,
according to the present invention it is not that
the subband LPC coefficients are coded, but the
fullband LPC coefficients is coded. Thus, band
division filter characteristics or the like which do
not need be transmitted are not contained in the LPC
coefficients, and it is thus possible to improve
coding performance of the LPC coefficients.
In addition, according to the present
invention the LPC coefficient band division is done
by the agency of the impulse response, and it is
CA 02355194 2001-07-31
possible to freely change the LPC prediction degree
of each subband.
Moreover, according to the present invention
the LPC analysis is executed before the band '
division with the band division filter. Thus, no
band division delay is generated, and the LPC
analysis window position is not limited by the band
division filter.
Changes in construction will occur to those
skilled in the art and various apparently different
modifications and embodiments may be made without
departing from the scope of the present invention.
The matter set forth in the foregoing description
and accompanying drawings is offered by way of
illustration only. It is therefore intended that
the foregoing description be regarded as
illustrative rather than limiting.
26
