Apparatus and method for decoding audio signal coding in a...

Details Apparatus and method for decoding audio signal coding in a... Apparatus and method for decoding audio signal coding in a...

2000-06-21

2002-09-24

Dorvil, Richemond (Department: 2641)

Data processing: speech signal processing, linguistics, language

Speech signal processing

For storage or transmission

C704S201000, C704S211000, C704S236000

Reexamination Certificate

active

06456966

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a deciding apparatus for deciding an audio signal coding system and a deciding method using the same and, more particularly, a deciding apparatus for deciding an audio signal coding system using a DSP (Digital Signal Processor) and a deciding method using the same.
In recent years, the audio sources such as CD, LD, DVD, etc. have been spread and also PCM (Pulse Code Modulation), DTS, AC-3, MPEG, etc. have been practically used as the coding system for the audio signal recorded thereon. In order to decode the audio signals to which these coding systems are applied, the decoding methods that mate with the coding systems must be employed. Therefore, prior to the decoding of the audio signal, the coding system that has been applied to the audio signal must be decided.
The audio signal is input from the audio source (CD, LD, DVD, etc.) to the AV amplifier, the DVD player, the speaker system, etc. The audio signal from CD, LD, DVD is coded and the coding system is different for every audio source. The coding systems are shown in Table 1.
TABLE 1
Audio source
Available Coding system
CD
PCM, DTS
LD
PCM, DTS, AC-3, MPEG
DVD
PCM, DTS, AC-3, MPEG
In Table 1, DTS is the coding system developed by Digital Theater Systems, Inc., AC-3 is the coding system developed by Dolby Research Institute, and MPEG (Moving Picture Experts Group) is the international standard of the information compressed coding system.
As can seen from Table 1, only a single coding system is not always applied to one audio source, but a plurality of coding systems may be applied to one audio source in some cases. In this case, the coding system may be changed in the middle of listening of one audio source. For example, there is such a case that, since DTS, AC-3, or MPEG can be applied to the DVD, first the audio source coded by DTS is listened and then switched to the same audio source coded by AC-3 or MPEG in the middle.
Therefore, in order to decode the audio signal, first it must be decided which coding system is applied to the audio signal at present. Then, the audio signal must be decoded according to the decoding method that corresponds to the decided coding system.
In the following, the deciding apparatus for deciding audio signal coding system employed in the prior art will be explained with reference to
FIG. 1
hereunder.
FIG. 1
is a block diagram showing a deciding apparatus for deciding audio signal coding system in the prior art. In
FIG. 1
,
100
denotes a DIR (Digital Interface Receiver). The audio signal supplied from the audio source is converted into a predetermined signal format by the DIR
100
, and then input into a DSP (Digital Signal Processor)
103
.
The audio signal from the audio source is based on the digital audio interface standard called IEC958, and one frame of the audio signal consists of audio data and additional data. An information indicating that the audio signal is coded by either the PCM or a coding system (DTS, AC-3, or MPEG) other than the PCM is contained in the additional data.
If the audio signal is coded by the PCM, the DIR
100
turns ON a flag indicating this (referred to as a “PCM flag” hereinafter) based on this information, and then outputs the PCM flag to a microcomputer
101
. Also, if the audio signal is coded by a coding system other than the PCM, the DIR
100
turns OFF the PCM flag, and then outputs the PCM flag to the microcomputer
101
. Based on ON/OFF of the PCM flag, the microcomputer
101
can decide whether the present audio signal input is coded by a PCM or the coding system (DTS, AC-3, or MPEG) other than the PCM. However, if the audio signal is coded by a coding system other than the PCM, it cannot be decided only by the PCM flag which one of DTS, AC-3, and MPEG is used for the audio signal. A method of identifying DTS, AC-3, and MPEG in this case will be described later.
The DSP
103
decodes the audio signal input from the DIR
100
. In order to decode the audio signal, the decode program which corresponds to the coding system applied to the audio signal must be previously loaded onto the DSP
103
. The decode program necessary for the decoding is stored in a memory
102
in the microcomputer
101
, and the program is loaded onto the DSP
103
according to the coding system applied to the audio signal.
Also, if the decode program which does not mate with the coding system applied to the audio signal is loaded onto the DSP
103
, such DSP
103
has a function for outputting the decode error signal to the microcomputer
101
. For example, since the coding system does not coincide with the decode program which is being loaded in case the coding system of the audio signal is changed in the middle of listening to the certain audio source, the DSP
103
outputs the decode error signal to the microcomputer
101
. Accordingly, the microcomputer
101
can detect that the coding system of the audio signal has been changed.
Reference numeral
105
denotes an output mute device for muting the output from the DSP, and
104
denotes a D/A converter for converting the digital signal output from the DSP into the analog signal.
Next, a deciding method for deciding audio signal coding system using the deciding apparatus for deciding the audio signal coding system shown in
FIG. 1
will be explained with reference to FIG.
2
.
FIG.2
is a flowchart showing a process for deciding audio signal coding system programmed in the microcomputer
101
in the prior art.
First of all, in step S
101
, according to the ON/OFF-switching of the PCM flag being output from the DIR
100
or the decode error signal, the microcomputer
101
detects that the coding system of the audio signal from the audio source has been changed.
Then, in step S
102
, the microcomputer
101
outputs the output mute signal to the output mute device
104
to mute the output.
In turn, in step S
103
, the microcomputer
101
outputs the decode program halt instruction to the DSP
103
to halt the current decode process being executed in the DSP
103
.
Then, in step S
104
, it is decided whether or not the coding system of the audio signal supplied from the audio source is either the PCM system or another system (DTS, AC-3, or MPEG). This decision is made based on ON/OFF of the PCM flag from the DIR
100
. In other words, the microcomputer
101
decides that the coding system is the PCM system if the PCM flag is ON, while it decides that the coding system is another system (DTS, AC3, or MPEG) if the PCM flag is OFF.
At this time, in step S
104
, if it is decided that the coding system of the audio signal from the audio source is the PCM system (if YES), the process goes to step S
105
. Then, the PCM decode program stored in the memory
102
is loaded onto the DSP
103
. Then, the process goes to step S
106
, and the decode process start signal is output to the DSP
103
and the decode process is restarted in the DSP
103
. After this, the process advances to step S
107
, and then the microcomputer
101
outputs the output mute release signal to the output mute device
104
to release the output mute, whereby the process for deciding audio signal coding system is ended.
In contrast, in step S
104
, if it is decided that the coding system of the audio signal from the audio source is not the PCM system (if NO), the process goes from step S
104
to step S
108
. Then, in step S
108
, the DTS decode program is loaded from the memory
102
onto DSP
103
. Then, the process advances to step S
109
, where the microcomputer
101
outputs the decode process start signal to the DSP
103
to cause the DSP
103
to restart the decode process. Then, the process goes to step S
110
, where the microcomputer
101
decides whether or not the decode error signal supplied from the DSP
103
is present. Such decode error signal is output from the DSP
103
to the microcomputer
101
when the coding system applied to the audio signal currently does not coincide with the decode program loaded onto the DSP
103
. For this reason, in step S
110
, if there is no decode error sign

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