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Claims  |
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We claim:
1. Coding transmission equipment for communication of an input signal,
comprising:
a transmitter device, comprising:
a plurality of adaptive coding units each including an adaptive quantizer,
operatively connected to receive the input signal, for outputting a
quantized value according to the input signal and an error calculating
unit, operatively connected to said adaptive quantizer, for calculating a
quantization error of said adaptive quantizer, said adaptive quantizer in
each of said adaptive coding units having a different updating speed of
quantizing step size;
an evaluating unit, operatively connected to said error calculating unit in
each of said adaptive coding units, for outputting decision information
indicating which of said adaptive coding units should be selected as an
optimum adaptive coding unit to carry out optimum quantization at every
frame of the input signal in dependence upon the quantization errors
output by said error calculating unit in each of said plurality of
adaptive coding units; and
a sending unit, operatively connected to said adaptive quantizer in each of
said adaptive coding units and said evaluating unit, for selecting an
optimum quantized value output by the optimum adaptive coding unit in
dependence upon the decision information output by said evaluating unit
and transmitting the optimum quantized value together with the decision
information identifying the optimum adaptive coding unit;
a receiver device receiving the optimum quantized value and the decision
information in a received signal, comprising:
a dividing unit for dividing the received signal from said transmitter
device into the quantized value and the decision information;
an adaptive decoding unit, operatively connected to said dividing unit, for
decoding the quantized value obtained by said dividing unit into the
original input signal; and
an optimum control unit, operatively connected to said dividing unit and
said adaptive decoding unit, for controlling an updating speed of a
quantizing step size of said adaptive decoding unit to coincide with the
updating speed of the quantizing step size of the optimum adaptive coding
unit in dependence upon the decision information obtained by said dividing
unit.
2. Coding transmission equipment according to
wherein said transmitter device further comprises a parameter copy unit,
operatively connected to said adaptive coding units and said evaluating
unit, for storing parameters determining inner conditions of each of said
adaptive coding units and for outputting an optimum parameter of the
optimum adaptive coding unit selected by said evaluating unit to said
adaptive coding units at every frame, and
wherein each of said adaptive coding units starts a signal process for a
next frame after changing one of the inner conditions in accordance with
the optimum parameter from said parameter copy unit.
3. Coding transmission equipment according to claim 2,
wherein said transmitter device further comprises an error correction
coding unit, operatively connected to said evaluating unit and said
sending unit, for carrying out an error correction coding process on the
decision information from said evaluating unit and outputting processed
decision information to be sent to said receiver device, and
wherein said receiver device further comprises an error correcting unit,
operatively connected to said dividing unit and said optimum control unit,
for carrying out an error correcting process on the decision information
obtained by said dividing unit and outputting error corrected decision
information to said optimum control unit.
4. Coding transmission equipment according to claim 2,
wherein said receiver device further comprises a post-processing filter,
operatively connected to said adaptive decoding unit, having a parameter,
and
wherein said adaptive decoding unit has a parameter and the parameter of
said post-processing filter is varied in dependence upon changes in the
parameter of said adaptive decoding unit.
5. Coding transmission equipment according to claim 2, wherein each said
adaptive coding unit is an adaptive differential pulse code modulation
coder.
6. Coding transmission equipment according to claim 2, wherein each said
adaptive coding unit comprises:
a subtractor, operatively connected to receive the input signal, for
calculating a prediction error corresponding to a difference between the
input signal and a predicted value;
an adaptive quantizer, operatively connected to said subtractor and said
sending unit, for adaptive quantization of the prediction error to produce
the quantized value;
an adaptive inverse quantizer, operatively connected to said adaptive
quantizer, for adaptive inverse quantization of the quantized value from
said adaptive quantizer to produce an inverse quantized value;
a predictor, operatively connected to said adaptive inverse quantizer and
said subtractor, for calculating the predicted value in dependence upon
prior inverse quantized values produced by said adaptive inverse
quantizer; and
an error calculating unit, operatively connected to said subtractor and
said adaptive inverse quantizer, for calculating the quantization error
corresponding to a differential value between the prediction error and the
inverse quantized value from said adaptive inverse quantizer.
7. Coding transmission equipment according to claim 6, wherein said
predictor includes a zero predictor and a pole predictor each operatively
connected to said adaptive inverse quantizer and said subtractor.
8. Coding transmission equipment according to claim 2, wherein the optimum
parameter of the optimum adaptive coding unit to be copied by said
parameter copy unit includes a quantization step size updating
coefficient.
9. Coding transmission equipment according to claim 8, wherein the optimum
parameter to be copied further includes tap data and a prediction
coefficient of said predictor.
10. A transmitter device, used in coding transmission equipment, for
carrying out coding of an input signal with adaptive quantization,
comprising:
a plurality of adaptive coding units each including an adaptive quantizer,
operatively connected to receive the input signal, for outputting a
quantized value according to the input signal and an error calculating
unit, operatively connected to said adaptive quantizer, for calculating a
quantization error of said adaptive quantizer, said adaptive quantizer in
each of said adaptive coding units having a different updating speed of a
quantizing step size;
an evaluating unit, operatively connected to said error calculating unit in
each of said adaptive coding units, for outputting decision information
indicating which of said adaptive coding units should be selected as an
optimum adaptive coding unit to carry out optimum quantization at every
frame of the input signal in dependence upon the quantization error output
by said error calculating unit in each of said plurality of adaptive
coding units; and
a sending unit, operatively connected to said adaptive quantizer in each of
said adaptive coding units and said evaluating unit, for selecting an
optimum quantized value output by the optimum adaptive coding unit in
dependence upon the decision information output by said evaluating unit
and transmitting an optimum quantized value together with the decision
information identifying the optimum adaptive coding unit.
11. A transmitter device according to claim 10, further comprising a
parameter copy unit, operatively connected to said adaptive coding units
and said evaluating unit, for storing parameters determining inner
conditions of each of said adaptive coding units and for outputting an
optimum parameter of the optimum adaptive coding unit selected by said
evaluating unit to said adaptive coding units at every frame, and
wherein each of said adaptive coding units starts a signal process for a
next frame after changing one of the inner conditions in accordance with
the optimum parameter from said parameter copy unit.
12. A transmitter device according to claim 11, wherein each said adaptive
coding unit is an adaptive differential pulse code modulation coder.
13. A transmitter device according to claim 11, wherein each said adaptive
coding unit comprises:
a subtractor, operatively connected to receive the input signal, for
calculating a prediction error corresponding to a difference between the
input signal and a predicted value;
an adaptive quantizer, operatively connected to said subtractor and said
sending unit, for adaptive quantization of the prediction error to produce
the quantized value;
an adaptive inverse quantizer, operatively connected to said adaptive
quantizer, for adaptive inverse quantization of the quantized value from
said adaptive quantizer to produce an inverse quantized value;
a predictor, operatively connected to said adaptive inverse quantizer and
said subtractor, for calculating the predicted value in dependence upon
prior inverse quantized values produced by said adaptive inverse
quantizer; and
an error calculating unit, operatively connected to said subtractor and
said adaptive inverse quantizer, for calculating the quantization error
corresponding to a differential value between the prediction error and the
inverse quantized value from said adaptive inverse quantizer.
14. A transmitter device according to claim 13, wherein said predictor
includes a zero predictor and a pole predictor each operatively connected
to said adaptive, quantizer and said subtractor.
15. A transmitter device according to claim 11, wherein the parameter of
the optimum adaptive coding unit to be copied by said parameter copy unit
includes a quantization step size updating coefficient.
16. A transmitter device according to claim 15, wherein the parameter to be
copied further includes tap data and a prediction coefficient of said
predictor.
17. Coding transmission equipment for communication of an input signal,
comprising:
a transmitter device, comprising:
a plurality of adaptive coding units each including an adaptive quantizer,
operatively connected to receive the input signal, for outputting a
quantized value according to the input signal and an error calculating
unit, operatively connected to said adaptive quantizer, for calculating a
quantization error of said adaptive quantizer, said adaptive quantizer in
each of said adaptive coding units having a different updating speed of
quantizing step size determined in dependence upon an individual
prediction coefficient;
a plurality of adaptive weighting filters, each operatively connected to
said error calculating unit in a corresponding one of said adaptive coding
units, each weighting the quantization error with the individual
prediction coefficient used in the corresponding one of said adaptive
coding units, each of said adaptive weighting filters outputting an
additional quantization error in which a hearing characteristic is taken
into consideration;
an evaluating unit, operatively connected to said adaptive weighting
filters, for outputting decision information indicating which of said
adaptive coding units should be selected as an optimum adaptive coding
unit to carry out optimum quantization at every frame of the input signal
in dependence upon the additional quantization errors output by said
adaptive weighting filters; and
a sending unit, operatively connected to said adaptive quantizer in each of
said adaptive coding units and said evaluating unit, for selecting an
optimum quantized value output by the optimum adaptive coding unit in
dependence upon the decision information output by said evaluating unit
and transmitting the optimum quantized value together with the decision
information identifying the optimum adaptive coding unit;
a receiver device receiving the optimum quantized value and the decision
information in a received signal, comprising:
a dividing unit for dividing the received signal from said transmitter
device into the quantized value and the decision information;
an adaptive decoding unit, operatively connected to said dividing unit, for
decoding the quantized value obtained by said dividing unit into the
original input signal; and
an optimum control unit, operatively connected to said dividing unit and
said adaptive decoding unit, for controlling an updating speed of a
quantizing step size of said adaptive decoding unit to coincide with the
updating speed of the quantizing step size of the optimum adaptive coding
unit in dependence upon the decision information obtained by said dividing
unit.
18. Coding transmission equipment according to claim 17,
wherein said transmitter device further comprises:
a first parameter copy unit, operatively connected to said adaptive coding
units and said evaluating unit, for storing parameters determining inner
conditions of each of said adaptive coding units and for outputting and
optimum coding parameter of the optimum adaptive coding unit selected by
said evaluating unit to said adaptive coding units at every frame; and
a second parameter copy unit, operatively connected to said adaptive
weighting filters and said evaluating unit, for storing parameters
determining inner conditions of each of said adaptive weighting filters
and for outputting an optimum filter parameter of said adaptive weighting
filter in the optimum adaptive coding unit selected by said evaluating
unit to said adaptive weighting filters at every frame, and
wherein each of said adaptive coding units starts a signal coding process
for a next frame after changing one of the inner conditions therein in
accordance with the optimum coding parameter from said parameter copy unit
and each of said adaptive weighting filters starts a signal filtering
process for the next frame after changing one of the inner conditions
therein in accordance with the optimum filter parameter from said
additional parameter copy unit.
19. Coding transmission equipment according to claim 18,
wherein said transmitter device further comprises an error correction
coding unit, operatively connected to said evaluating unit and said
sending unit, for carrying out an error correction coding process on the
decision information from said evaluating unit and outputting processed
decision information to be sent to said receiver device, and
wherein said receiver device further comprises an error correcting unit,
operatively connected to said dividing unit and said optimum control unit,
for carrying out an error correcting process on the decision information
obtained by said dividing unit and outputting error corrected decision
information to said optimum control unit.
20. Coding transmission equipment according to claim 18,
wherein said receiver device further comprises a post-processing filter,
operatively connected to said adaptive decoding unit, having a parameter,
and
wherein said adaptive decoding unit has a parameter and the parameter of
said post-processing filter is varied in dependence upon changes in the
parameter of said adaptive decoding unit.
21. Coding transmission equipment according to claim 18, wherein said
adaptive coding units have a processing characteristic varying by a
difference in quantization step size updating coefficients between said
adaptive quantizers.
22. Coding transmission equipment according to claim 18, wherein each said
adaptive coding unit is an adaptive differential pulse code modulation
coder.
23. Coding transmission equipment according to claim 18, wherein each said
adaptive coding unit comprises:
a subtractor, operatively connected to receive the input signal, for
calculating a prediction error corresponding to a difference between the
input signal and a predicted value;
an adaptive quantizer, operatively connected to said subtractor and said
sending unit, for adaptive quantization of the prediction error to produce
the quantized value;
an adaptive inverse quantizer, operatively connected to said adaptive
quantizer, for adaptive inverse quantization of the quantized value from
said adaptive quantizer to produce an inverse quantized value;
a predictor, operatively connected to said adaptive inverse quantizer and
said subtractor, for calculating the predicted value in accordance with a
characteristic determined in dependence upon prior inverse quantized
values produced by said adaptive inverse quantizer;
an adder, operatively connected to the output of said adaptive inverse
quantizer and to the output of said predictor, for calculating a
reproduced signal; and
an error calculating unit, operatively connected to receive the input
signal and the reproduced signal, for calculating the quantization error
by subtracting the reproduced signal from the input signal.
24. Coding transmission equipment according to claim 23, wherein said
transmitter device further comprises additional filters, each
corresponding to one of said adaptive weighting filters and having an
inverse characteristic of the characteristic of said predictor in the
corresponding one of said adaptive coding units.
25. Coding transmission equipment according to claim 23, wherein said
predictor includes a zero predictor and a pole predictor each operatively
connected to said adaptive inverse quantizer and said subtractor.
26. Coding transmission equipment according to claim 23, wherein the
optimum coding parameter of the optimum adaptive coding unit to be copied
by said parameter copy unit includes a quantization step size updating
coefficient.
27. Coding transmission equipment according to claim 26, wherein the
optimum coding parameter to be copied further includes tap data and a
prediction coefficient of said predictor.
28. Coding transmission equipment according to claim 18, wherein each said
adaptive coding unit comprises:
a first subtractor, operatively connected to receive the input signal, for
calculating a prediction error corresponding to a difference between the
input signal and a predicted value;
an adaptive quantizer, operatively connected to said first subtractor and
said sending unit, for adaptive quantization of the prediction error to
produce the quantized value;
an adaptive inverse quantizer, operatively connected to said adaptive
quantizer, for adaptive inverse quantization of the quantized value from
said adaptive quantizer to produce an inverse quantized value;
a predictor, operatively connected to said adaptive inverse quantizer and
said first subtractor, for calculating the predicted value in dependence
upon prior inverse quantized values produced by said adaptive inverse
quantizer; and
a second subtractor, operatively connected to the output of said adaptive
inverse quantizer and to the output of said first subtractor, for
calculating the quantization error by subtracting the output of said
adaptive inverse quantizer from the output of said first subtractor.
29. Coding transmission equipment according to claim 28, wherein said
transmitter device further comprises additional filters, each
corresponding to one of said adaptive weighting filters and having an
inverse characteristic of the characteristic of said predictor in the
corresponding one of said adaptive coding units.
30. Coding transmission equipment according to claim 28, wherein said
predictor includes a zero predictor and a pole predictor each operatively
connected to said adaptive inverse quantizer and said first subtractor.
31. Coding transmission equipment according to claim 26, wherein the
optimum coding parameter of the optimum adaptive coding unit to be copied
by said parameter copy unit includes a quantization step size updating
coefficient.
32. Coding transmission equipment according to claim 31, wherein the
optimum coding parameter to be copied further includes tap data and a
prediction coefficient of said predictor.
33. A transmission device, used in coding transmission equipment, for
carrying out coding of an input signal with adaptive quantization,
comprising:
a plurality of adaptive coding units each including an adaptive quantizer,
operatively connected to receive the input signal, for outputting a
quantized value according to the input signal and an error calculation
unit, operatively connected to said adaptive quantizer, for calculating a
quantization error of said adaptive quantizer, said adaptive quantizer in
each of said adaptive coding units having a different updating speed of
quantizing step size determined in dependence upon an individual
prediction coefficient;
a plurality of adaptive weighting filters, each operatively connected to
said error in a corresponding one of said adaptive coding units, each for
weighting the quantization error with the individual prediction
coefficient used in the corresponding one of said adaptive coding units,
each of said adaptive weighting filters outputting an additional
quantization error in which a hearing characteristic is taken into
consideration;
an evaluating unit, operatively connected to said adaptive weighting
filters, for outputting decision information indicating which of said
adaptive coding units should be selected as an optimum adaptive coding
unit to carry out optimum quantization at every frame of the input signal
in dependence upon the additional quantization errors output by said
adaptive weighting filters; and
a sending unit, operatively connected to said adaptive quantizer in each of
said adaptive coding units and said evaluating unit, for selecting an
optimum quantized value output by the optimum adaptive coding unit, in
dependence upon the decision information output by said evaluating unit
and transmitting the optimum quantized value together with the decision
information identifying the optimum adaptive coding unit.
34. A transmission device according to claim 33,
further comprising:
a first parameter copy unit, operatively connected to said adaptive coding
units and said evaluating unit, for storing parameters determining inner
conditions of each of said adaptive coding units and for outputting an
optimum coding parameter of the optimum adaptive coding unit selected by
said evaluating unit to said adaptive coding units at every frame; and
a second parameter copy unit, operatively connected to said adaptive
weighting filters and said evaluating unit, for storing parameters
determining inner conditions of each of said adaptive weighting filters
and for outputting an optimum filter parameter of said adaptive weighting
filter in the optimum adaptive coding unit selected by said evaluating
unit to said adaptive weighting filters at every frame, and
wherein each of said adaptive coding units starts a signal coding process
for a next frame after changing one of the inner conditions therein in
accordance with the optimum coding parameter from said parameter copy unit
and each of said adaptive weighting filters starts a signal filtering
process for the next frame after changing one of the inner conditions
therein in accordance with the optimum filter parameter from said
additional parameter copy unit.
35. A transmission device according to claim 33, wherein said plurality of
adaptive coding units have a processing characteristic varying by a
difference in quantization step size updating coefficients between said
adaptive quantizers.
36. A transmitter device according to claim 33, wherein each said adaptive
coding unit is an adaptive differential pulse code modulator coder.
37. A transmission device according to claim 33, wherein each said adaptive
coding unit comprises:
a subtractor, operatively connected to receive the input signal, for
calculating a prediction error corresponding to a difference between the
input signal and a predicted value;
an adaptive quantizer, operatively connected to said subtractor and said
sending unit, for adaptive quantization of the prediction error to produce
the quantized value;
an adaptive inverse quantizer, operatively connected to said adaptive
quantizer, for adaptive inverse quantization of the quantized value from
said adaptive quantizer to produce an inverse quantized value;
a predictor, operatively connected to said adaptive inverse quantizer and
said subtractor, for calculating the predictor value in accordance with a
characteristic determined in dependence upon prior inverse quantized
values produced by said adaptive inverse quantizer;
an adder, operatively connected to the output of said adaptive inverse
quantizer and to the output of said predictor, for calculating a
reproduced signal; and
an error calculating unit, operatively connected to receive the input
signal and the reproduced signal, for calculating the quantization error
by subtracting the reproduced signal from the input signal.
38. A transmission device according to claim 37, wherein further comprising
additional filters, each corresponding to one of said adaptive weighting
filters and having an inverse characteristic of the characteristic of said
predictor in the corresponding one of said adaptive coding units.
39. A transmission device according to claim 33, wherein said predictor
includes a zero predictor and a pole predictor each operatively connected
to said adaptive inverse quantizer and said subtractor.
40. A transmission device according to claim 33, wherein the optimum coding
parameter of the optimum adaptive coding unit to be copied by said
parameter copy unit includes a quantization step size updating
coefficient.
41. A transmission device according to claim 40, wherein the optimum coding
parameter to be copied further includes tap data and a prediction
coefficient of said predictor.
42. A transmission device according to claim 35, wherein each said adaptive
coding unit comprises:
a first subtractor, operatively connected to receive the input signal, for
calculating a prediction error corresponding to a difference between the
input signal and a predicted value;
an adaptive quantizer, operatively connected to said first subtractor and
said sending unit, for adaptive quantization of the prediction error to
produce the quantized value;
an adaptive inverse quantizer, operatively connected to said adaptive
quantizer, for adaptive inverse quantization of the quantized value from
said adaptive quantizer to produce an inverse quantized value;
a predictor, operatively connected to said adaptive inverse quantizer and
said first subtractor, for calculating the predicted value in dependence
upon prior inverse quantized values produced by said adaptive inverse
quantizer; and
a second subtractor, operatively connected to the output of said adaptive
inverse quantizer and to the output of said first subtractor, for
calculating the quantization error by subtracting the output of said
adaptive inverse quantizer from the output of said first subtractor.
43. A transmission device according to claim 42, wherein said transmitter
device further comprises additional filters, each corresponding to one of
said adaptive weighting filters and having an inverse characteristic of
the characteristic of said predictor in the corresponding one of said
adaptive coding units.
44. A transmission device according to claim 42, wherein said predictor
includes a zero predictor and a pole predictor each operatively connected
to said adaptive inverse quantizer and said first subtractor.
45. A transmission device according to claim 42, wherein the optimum coding
parameter of the optimum adaptive coding unit to be copied by said
parameter copy unit includes a quantization step size updating
coefficient.
46. A transmission device according to claim 45, wherein the optimum coding
parameter to be copied further includes tap data and a prediction
coefficient of said predictor. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coding transmission equipment in which an
input signal, such as a voice signal or a picture signal, is coded and
transmitted to a receiver side from a transmitter side and a received
signal is decoded to become an original signal at the receiver side. In
particular, the present invention relates to low bit rate coding equipment
(bandwidth compression coding equipment), such as an ADPCM (Adaptive
Differential Pulse Code Modulation) system CODEC (COder and DECoder),
which carries out low bit rate coding of a voice or picture signal.
When the voice signal, etc., is transmitted, bandwidth compression is
required to ensure an efficient utilization of a transmission line. The
low bit rat coding transmission equipment for the voice signal carries out
information compression while maintaining the quality of the voice signal,
which enables a reduction of line costs for the transmission of the voice
information in equipment used for, for example, mobile radio
communication, satellite communication, or office inter communication
system, and a reduction of storage capacity needed, for example, for the
storage of voice information in an audio response system.
2. Description of the Related Art
ADPCM coding equipment is related to the present invention in that it
carries out coding by adaptive quantization. In the ADPCM coding
equipment, a prediction error E corresponding to a difference between a
current input signal X and a predicted value X obtained on the basis of
past input signals is produced and quantized at the transmitter side. At
this time, adaptive quantization, in which the size of a quantizing step
is increased or decreased in accordance with a quantizing level of a
signal sampled just prior to the current sampled signal, is carried out in
order to realize a quick adaptation to a sudden change of the predicted
error, instead of uniform quantization, whereby a high quality recovered
signal is realized.
In this case, however, the sizes to which the quantizing step can increased
or decreased are limited, and therefore, when the input signals are voice
signals, for example, a voiced sound, an unvoiced sound, or a
voicelessness, etc., the nature of the signals changes from moment to
moment and the coding system of the prior art cannot cope with these rapid
variations in the voice signal. As a result, an optimum quantization is
not realized, and thus the voice recovered at the receiver side has a poor
quality.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide coding
transmission equipment which can obtain a high quality recovered signal,
for example, a voice signal recovered at a receiver side.
According to a fundamental aspect of the present invention, there is
provided coding transmission equipment having a transmitter device and a
receiver device wherein, the transmitter device comprises a plurality of
adaptive coding units including an adaptive quantizer for outputting a
quantized value according to an input signal, and an error calculating
unit for calculating the quantization error of the adaptive quantizer,
each of the adaptive coding units having different adaptive quantizer
processing characteristics; an evaluating unit for deciding which is the
optimum adaptive coding unit to carry out an optimum quantization, from
among the plurality of adaptive coding units, at every frame of the input
signal on the basis of the quantization errors input from the plurality of
adaptive coding units respectively; and a sending unit for selecting the
optimum quantized value of the optimum adaptive coding unit from among the
quantized values input from the plurality of adaptive coding units,
respectively, on the basis of the decision of the evaluating unit, and
transmitting the optimum quantized value together with the decision
information; the receiver device comprises a dividing unit for dividing a
signal received from the transmitter device into the optimum quantized
value and the decision information; an adaptive decoding unit for decoding
the optimum quantized value obtained by the dividing unit into the
original input signal; and an optimum controlling unit for controlling the
processing characteristic of the adaptive decoding unit to an optimum
processing characteristic according to the decision information obtained
by the dividing unit.
According to another aspect of the present invention, the transmitter
device further comprises a parameter copy unit in which parameters for
determining an inner condition of the adaptive coding unit are input from
all of the adaptive coding units, and an optimum parameter of the optimum
adaptive coding unit is selected and sent to other adaptive coding units
at every frame according to the decision of the evaluating unit; wherein
each of the other adaptive coding units starts the signal process for a
next frame after copying the optimum parameter sent from the parameter
copy unit, as an own parameter.
According to still another aspect of the present invention, the transmitter
device further comprises an error correction coding unit for carrying out
an error correction coding process for the decision information from the
evaluating unit, whereby the decision information processed by the error
correction coding is sent to the receiver device; and the receiver device
further comprises an error correcting unit for carrying out the error
correcting process for the decision information obtained by the dividing
unit, whereby the error corrected decision information is sent to the
optimum controlling unit.
According to a still further aspect of the present invention, the
transmitter device further comprises
a plurality of adaptive weighting filters each effecting weighting on said
quantization error with the same prediction coefficient as said prediction
coefficient used in the corresponding one of said adaptive coding units,
whereby an additional error signal in which a masking effect is taken into
consideration is sent to the evaluation unit.
According to yet another aspect of the present invention, the receiver
device further comprises a post-processing filter disposed at a latter
stage of tee adaptive decoding unit, wherein the parameter of the
post-processing filter is varied according to the parameter of the
adaptive decoding unit.
BRIEF DESCRIPTION OF THE DRAWINGS
Examples of coding transmission equipment in accordance with the present
invention will be described with reference to the accompanying drawings,
in which
FIG. 1 shows a prior art ADPCM coder;
FIG. 2 shows a prior art ADPCM decoder;
FIG. 3 shows an embodiment of an ADPCM decoder at a receiver side of the
coding transmission equipment according to the present invention;
FIG. 4 shows an embodiment of an ADPCM decoder at a receiver side of the
coding transmission equipment according to the present invention;
FIG. 5 shows an adaptive differential coding unit of the ADPCM coder of
FIG. 3 in more detail;
FIG. 6 shows another embodiment of the ADPCM coder according to the present
invention;
FIG. 7 shows a further embodiment of the coding transmission equipment
according to the present invention;
FIG. 8 shows an example of an error correcting code;
FIG. 9 shows a format of the transmission signal including the error
correcting code;
FIG. 10 shows an example of an error correction at the receiver side;
FIG. 11 shows still another embodiment of the ADPCM decoder at the receiver
side according to the present invention;
FIG. 12 is a view for explaining a post-processing filter in detail;
FIG. 13 is a graph showing the relationship between the noise threshold and
the signal amplitude;
FIG. 14 shows still another embodiment of the ADPCM coder according to the
present invention;
FIG. 15 shows an embodiment of a detailed construction of a part of the
ADPCM coder shown in FIG. 14; and
FIG. 16 shows another embodiment of the detailed construction of a part of
the ADPCM coder shown in FIG. 14.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For a better understanding of the preferred embodiment, the problems in the
prior art will be first explained with reference to FIGS. 1 and 2.
FIG. 1 shows an adaptive differential coder on the transmitter side in a
prior art low bit rate coding transmission equipment for a voice signal.
In FIG. 1, the coder comprises a subtractor 10 for calculating a
prediction error E(n) corresponding to a difference between an input voice
signal X(n) and a predicted value X(n) to be output; an adaptive quantizer
11 for adaptive quantizing of the prediction error E(n) to output the
quantized value I(n) as a transmission signal; an adaptive inverse
quantizer 12 for adaptive inverse quantizing of the quantized value I(n);
an adder 13 for adding the inverse quantized value E(n) of the prediction
error E(n) from the inverse quantizer 12 and the predicted value X(n); an
adaptive zero predictor 14 for producing a zero predicted value X(n).sub.z
; an adaptive pole predictor 15 for producing a pole predicted value
X(n).sub.p ; and an adder 16 for adding the zero predicted value
X(n).sub.z and the pole predicted value X(n).sub.p to produce the
predicted value X(n).
In this adaptive differential coder, the quantizer 11, the inverse
quantizer 12, the zero predictor 14, and the pole predictor 15 are
adaptive-controlled. For example, in the quantizer 11 and the inverse
quantizer 12, the adaptive quantization wherein the quantizing step size
.DELTA.(n) is updated according to the following formula is carried out.
.DELTA.(n+1)=.DELTA.(n).sup..gamma. .times.M(I(n)) (1)
where, .gamma. is a coefficient for gradually reducing the influence of the
line error, which has a value close to and lower than 1; and M(I(n)) is a
step size updating coefficient (or a step size updating speed).
When the quantized value I(n) from the quantizer 11 is, for example, a 1
bit output signal, the updating coefficient M(I(n)) assumes a value
.alpha. close to and lower than 1, for example, .alpha.=0.93, when the
quantized value I(n) is "0", and a value .beta. close to and higher than
1, for example, .beta.=1.31, when the quantized value I(n) is "1". Also,
when the quantized value I(n) is a plurality bit output signal, the step
size updating coefficient M(I(n)) is increased in proportion to the
increment of the number indicated by the plurality bit output signal.
FIG. 2 shows an adaptive differential decoder on the receiver side in a
prior art low bit rate coding transmission equipment.
In FIG. 2, the decoder comprises an inverse quantizer 71', an adder 73, a
zero predictor 75, a pole predictor 76, and an adder 77.
In this decoder, the quantized value I(n) of the prediction error
transmitted from the transmitter side is inverse-quantized by the inverse
quantizer 71 to recover the prediction error, and the zero predicted value
X(n).sub.z and the pole predicted value X(n).sub.p are produced by the
zero predictor 75 and the pole predictor 76 on the basis of the recovered
past prediction errors respectively. Then, the predicted value X(n)
obtained by adding this zero predicted value X(n).sub.z and the pole
predicted value X(n).sub.p by the adder 73 is added to the
inverse-quantized prediction error from the inverse quantizer 71' by the
adder 73, to recover the voice signal S(n). The processing characteristics
of the inverse quantizer 71', the zero predictor 75, and the pole
predictor 76 at the receiver side are the same as that of the inverse
quantizer 12, the zero predictor 14, and the pole predictor 15 at the
transmitter side, respectively.
In the differential coder of FIG. 1, the sep size updating coefficient
M(I(n)) of the quantizer 11 and the inverse quantizer 12 is a fixed value,
since the values .alpha. and .beta. which determine the updating
coefficient M(I(n)) are fixed. Therefore, sometimes the optimum
quantization is not carried out at the quantizer 11, since updating
coefficient M(I(n)) of the step size .DELTA.(n), which is a threshold for
quantizing the prediction error E(n), may not sufficiently follow the
change of the prediction error E(n).
In particular, when the input signal is a voice signal, the nature of the
signal, for example, a voiced sound, unvoiced sound, or silence, changes
from moment to moment and frequently varies, and therefore, the optimum
quantization is not carried out since the fixed step size updating
coefficient M(I(n)) cannot follow the change of the voice signal.
A preferred embodiment of the present invention will now be explained wit
reference to FIGS. 3 to 5. FIGS. 3 to 5 show an embodiment of the coding
transmission equipment, according to the present invention, which is
adapted to transmission equipment using the ADPCM coding system. FIG. 3
shows an ADPCM coder at the transmitter side, and FIG. 4 shows an ADPCM
decoder at the receiver side.
In FIG. 3, 1.sub.1 to 1.sub.k are the k numbers of adaptive differential
coding units in which the step size updating coefficients M(I(n)).sub.1 to
M(I(n)).sub.k of quantizers (in more detail, values .alpha. and .beta.
described above) are different, respectively. The fundamental structure is
the same as the adaptive differential coder shown in FIG. 1, except that a
subtractor is provided which calculates and outputs a quantization error
e(n) corresponding to a differential value between prediction error E(n)
and the inverse-quantized value of the prediction error E(n) from the
inverse quantizer 12.
FIG. 5 shows a more detailed structure of one of the adaptive differential
coding units 1.sub.1 to 1.sub.k. In FIG. 5, the subtractor 10 calculates
the prediction error E(n) corresponding to the differential value between
the input voice signal X(n) and the predicted value X(n) and sends this
prediction error E(n) to the adaptive quantizer 11. The adaptive quantizer
11 quantizes the prediction error E(n) and outputs a quantized value I(n).
This quantized value I(n) is introduced to the inverse quantizer 12, which
carries out the inverse quantization. At the same time, the quantized
value I(n) is transmitted to the receiver side. The inverse quantized
value E(n) of the prediction error E(n) from the inverse quantizer 12 is
introduced to the zero predictor 14 and the subtractor 17, and to the pole
predictor 15 via the adder 13. The predictor 14 produces a zero predicted
value X(n).sub.z, and the pole predictor 15 produces a pole predicted
value X(n).sub.p. The zero predicted value X(n).sub.z and the pole
predicted value X(n).sub.p are added by the adder 16 to produce a
predicted value X(n), which is then sent to the subtractor 10. The
subtractor 17 calculates the differential value between the prediction
error E(n) and the inverse quantized value E(n) thereof, and outputs the
result as a quantization error e(n).
The quantizer 11 and the inverse quantizer 12 are adaptive controlled type
devices, and the quantizing step size .DELTA.(n) is updated by the
quantizing step adapter (not shown) according to the formula (1) described
previously. This quantizing step size .DELTA.(n) is a parameter for
deciding inner conditions of the quantizer 11 and the inverse quantizer
12.
The zero predictor 14 and the pole predictor 15 are also adaptive control
type devices, and are constituted by circuits comprising taps (time delay
elements) and coefficient multipliers, having the orders l and m,
respectively. The zero predictor 14 and the pole predictor 15 hold
prediction coefficients updated in sequence, and from the viewpoint of the
transfer function as a filter, hold tap data containing past records.
That is, in the zero predictor 14, zero prediction coefficients C.sub.z
(1,n).about.C.sub.z (l, n) of each coefficient multiplier are updated by
the prediction coefficient adapter (not shown) according to the following
formula, respectively.
C.sub.z (i, n+1)=L.sub.z .times.C.sub.z (i, n)+D.sub.z
.times.sgn(E(n)).times.sgn(E(n-i) (2)
where, L.sub.z and D.su | | |
