Coding device

Details Coding device Coding device

2000-04-12

2001-12-04

Lam, Tuan T. (Department: 2816)

Coded data generation or conversion

Digital code to digital code converters

Adaptive coding

C341S050000

Reexamination Certificate

active

06326907

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a high-efficiency coding device for compressing and expanding digital data. More particularly, this invention relates to a coding device in which there is no overload distortion or the like.
BACKGROUND OF THE INVENTION
FIG. 18
is a diagram showing the constitution of a coding device using a type of conventional coding method known as an adaptive differential pulse code modulation (hereinafter ADPCM) method. In
FIG. 18
, reference numeral
1
represents a data input terminal,
2
represents a data output terminal, and
3
a
and
3
b
represent adders. Reference numeral
4
represents a step size adaptation unit for determining a coding step size in the ADPCM method, and
5
represents a differential coding unit for coding differential data based on the step size determined by the step size adaptation unit
4
. Reference numeral
6
represents a differential decoding unit for decoding differential data from the step size determined by the step size adaptation unit
4
and the data coded by the differential coding unit
5
, and
7
represents a one-sample delay unit for holding data of one sampling time.
The operation of the conventional coding device shown in
FIG. 18
will be explained below.
A coding device using an ADPCM method has the following two characteristic features. Firstly, it codes the differential value between present data to be coded and the immediately preceding data. Secondly, based on the result of coding the differential value, it adapts the step size so as to determine the step size in the next coding operation.
As a specific example, a case in which four bits of ADPCM data are obtained from sixteen bits of PCM data will be explained below.
The step size adaptation unit
4
performs the following processing to adapt the step size in accordance with data of the differential coding unit
5
. Since the input data are coded as four bits of ADPCM data, there are sixteen values of coded data from −8 to 7. For instance, when the coded data is −8 or 7, a coefficient of 2.4 is applied to the step size. Similarly, a coefficient of 2 is applied when the coded data is −7 or 6, a coefficient of 1.6 is applied when the coded data is −6 or 5, a coefficient of 1.2 is applied when the coded data is −5 or 4, and a coefficient of 0.9 is applied in all other cases. When this calculation produces a step size which is less than a predetermined minimum step size value, the step size is set to the minimum step size value. Furthermore, when the step size that has been calculated exceeds a predetermined maximum step size value, the step size is set to the maximum step size value.
The differential coding unit
5
subtracts the output of the adder
3
a
from the step size determined by the step size adaptation unit
4
. When the result of the subtraction is outside a range expressible by four bits, e.g. 8 or more, or −9 or less, a limit of 7 and −8 is respectively applied.
The differential decoding unit
6
multiplies the output of the differential coding unit
5
and the output of the step size adaptation unit
4
.
FIG. 19
shows specific calculation processes carried out by the coding device using the ADPCM method shown in FIG.
18
. The input data is in the form of a sin curve as shown in FIG.
20
.
In
FIG. 19
, “No.” represents the data number, “Input: PCM (hexadecimal)” is the PCM data input from the digital data input terminal
1
expressed in hexadecimal numbers. “Input: PCM (decimal)” is the value obtained by converting the hexadecimal data into decimal numbers. “Differential” is the output of the adding unit
3
a
. “Step size” represents the step size determined by the step size adaptation unit
4
. “Output: ADPCM data” represents the ADPCM data which has been coded by the differential coding unit
5
and output from the ADPCM coding data output terminal
2
. “Differential decode” represents the decoded value obtained by the differential decoding unit
6
. “Decoded data” is the output of the adder
3
b
, and “Difference between input and decoded data” represents the difference between the input PCM data and the decoded value of the ADPCM coded data (aforementioned decoded data).
The calculation process of the specific example shown in
FIG. 19
will be explained in sequence. This example refers to ADPCM coding, in which the initial value of the one-sample delay unit
7
is zero, and the initial value of the step size is 1. Furthermore, the minimum step size is 1, and the maximum step size is 4681.
In No. 1, since the input PCM value is zero and the initial value of the one-sample delay unit
7
is also zero, the output of the adder
3
a
is zero, and the output of the differential coding unit
5
(i.e. the output ADPCM data) is also zero. Further, the output of the differential decoding unit
6
is zero, and the decoded data is also zero. Prior to executing the data of No. 2, the step size adaptation unit
4
applies the coefficient of 0.9 (which is applied in all other cases as described above) to the initial value of 1. The result of this computation is 0.9, and since this is lower than the minimum step size value, the step size is set to a value of 1.
In No. 2, the input data is 1606, the value of the one-sample delay unit
7
is zero, the output of the adder
3
a
is 1606, and the output of the differential coding unit
5
is 7. Therefore, the output ADPCM data is also 7, the output of the differential decoding unit
6
is 7, and the output of the adder
3
b
is also 7. Consequently, the step size adapting unit
4
sets the step size to 2.4.
In No. 3, since the input is 3149 and the value of the one-sample delay unit
7
is 7, the output of the adder
3
a
is 3142, and the output of the differential coding unit
5
is 7. Therefore, the output ADPCM data is also 7, the output of the differential decoding unit
6
is 16.8, and the output of the adder
3
b
is 23.8. Consequently, the step size adaptation unit
4
sets the step size to 5.76. Subsequent computations are repeated in the same way, and further explanation will be omitted.
However, coding devices using the conventional ADPCM method described above have been known to suffer overload distortion and load distortion.
FIG. 21
shows decoded data obtained after coding the sin curve shown in
FIG. 20
in a coding device using the conventional ADPCM method.
FIG. 22
shows the difference between the input data shown in FIG.
20
and the decoded data obtained by the ADPCM method shown in FIG.
21
. As shown in
FIG. 22
, it is impossible to track the abrupt changes in the initial data, and a great distortion, known as overload distortion, occurs between the data from No. 1 to No. 11.
SUMMARY OF THE INVENTION
The present invention has been achieved in light of the problem of an inability to sufficiently track abrupt changes in the input data. It is an object of the present invention to provide a coding device in which no overload distortion occurs.
According to the present invention, input data is arranged into blocks, a maximum value MAX and a minimum value MIN in that block are determined. An orthogonal conversion computation unit subtracts the differential value of the maximum value MAX and the minimum value MIN from the input data, and then a coding unit performs coding the value calculated by the orthogonal conversion computation unit into desired bits. Therefore, coding can be achieved without overload distortion.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.


REFERENCES:
patent: 4677423 (1987-06-01), Benvenuto et al.
patent: 5825310 (1998-10-01), Tsutsui
“Computer Audio Processing”, T. Akui et al., Jun. 10, 1980, Akiba Shuppan K. K., pp. 38-43.
“Introduction to A/D and D/A Conversion Circuit”, I. Aira, Nov. 28, 1991, Nikkan Kogyo Shinbunsha, pp. 254-255.

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