Data processing: speech signal processing – linguistics – language – Speech signal processing – Psychoacoustic
Reexamination Certificate
2000-10-10
2002-10-01
{haeck over (S)}mits, T{overscore (a)}livaldis Ivars (Department: 2654)
Data processing: speech signal processing, linguistics, language
Speech signal processing
Psychoacoustic
C704S500000, C704S503000
Reexamination Certificate
active
06460016
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an audio decoding device for forming an audio signal by decoding coded signals transmitted by multi-channels of, for example, MPEG2, and also to a signal processing device for performing decoding by synchronizing audio compression signals such as MPEG audio signals or Dolby® AC-3 signals between an internal decoder and an external decoder.
2. Description of the Related Art
In MPEG2, for example, audio signals to be output simultaneously are transmitted through multi-channels.
In a bit stream by which the multi-channel signals are transmitted, channels for audio signals to be reproduced simultaneously are not proximate to each other and are arranged discretely timewise.
In order to decode and output the coded signals for the multi-channels in such a bit stream, signal decoding should be performed frame by frame as seen in an MPEG2 multi-channel decoder program provided by, for example, the FTP site of the University of California at Berkeley.
Alternatively, the coded signals on the channels arranged in the first half of the frame are temporarily stored in a memory, and then these coded signals are decoded while the coded signals on the channels arranged in the second half of the frame are decoded.
In either case, a large amount of coded signals need to be temporarily stored in a memory, which raises the required capacity of the memory and thus increases the size of the device.
Moreover, in order to perform the operation for decoding the coded signals, a memory capable of high-speed access should be used for temporarily storing the coded signals used for the operation. Since such a memory is expensive, reduction in the required capacity of the memory has been strongly demanded.
Regarding the necessity of a memory capable of high-speed access, a conventional decoding device
500
will be described with reference to FIG.
17
.
The decoding device
500
includes a memory section
510
and an operation section
520
. The operation section
520
includes a sub-band signal generation section
521
and a sub-band synthesis section
522
. When coded signals for n channels are given, the operation section
520
decodes the coded signals into sub-band signals. The sub-band signals for each channel is processed with a sub-band synthesis filter operation to generate an audio signal to be output. The memory section
510
includes a high-speed access memory such as an SRAM, which includes memory areas
511
through
514
for storing sub-band synthesis filter data and a memory area
515
for storing the sub-band signal data.
The decoding device
500
having the above-described structure operates in the following manner.
When the coded signals are input to the operation section
520
, the sub-band signal generation device
521
decodes the coded signals into sub-band signals and temporarily stores the sub-band signals in the memory area
515
. Then, the sub-band synthesis section
522
reads the sub-band signals from the memory area
515
and performs a sub-band synthesis filter operation of the sub-band signals. Thus, an audio signal is generated and output.
The sub-band synthesis filter data in the memory areas
511
through
514
is partially updated by the sub-band synthesis filter data generated from the sub-band signals in the memory area
515
. Accordingly, the operation section
520
needs to read the sub-band synthesis filter data from the memory section
510
when performing the sub-band synthesis filter operation and write again the sub-band synthesis filter data to the memory section
510
after the operation.
The memory section
510
needs to be a memory capable of high-speed access. In the case where the decoding device
500
corresponds to multi-channels, e.g., four channels, the memory section
510
needs to have four memory areas
511
through
514
so as to store sub-band synthesis filter data for the four channels.
A high-speed access memory such as an SRAM used for the memory section
510
needs to have a sufficiently large memory capacity to retain the sub-band synthesis filter data for at least four channels in order to perform real-time reproduction of four-channel data. Such a memory, which is generally expensive, significantly increases the cost of the audio decoding devices.
One format for digital audio interface is the IEC958 format. The IEC958 format is common for industrial and consumer uses. The sub-frame format thereof includes an area in which a synchronous preamble, AUX, 20-bit-unit audio data and other data can be added.
In the case of 2-channel transmission, a frame is formed by alternately repeating sub-frames for each of the two channels, and a block is formed of first through 192nd frames and then transmitted. The format of the audio data to be inserted into the sub-frames is not standardized. For example, a PCM signal formed by sampling an analog audio signal or a non-PCM signal (defined by the format described in ISO/IEC EC 11172-3:1993 and 13818-3:1996) such as compression audio data formed by sub-band coding.
In the case of reproducing coded signals for multi-channels (e.g., five channels of right forward, left forward, center, right rearward and left rearward) by an audio reproduction apparatus including a decoder, the coded signals for all the channels cannot always be decoded only by a built-in decoder (referred to as the “internal decoder”). Many general audio reproduction apparatuses output only audio signals in the right forward and left forward channels from the internal decoder. Such audio reproduction apparatuses require a separate decoder or a separate audio reproduction apparatus (referred to as the “external decoder”) in order to decode the coded signals for the other channels.
In order to synchronize an audio signal output from the internal decoder and an audio signal output from the external decoder while transmitting a non-PCM signal of the IEC958 format from the internal decoder to the external decoder, a conventional audio reproduction apparatus requires a buffer memory for performing synchronization between the internal decoder and the external decoder. Such a buffer memory needs to have a sufficiently large capacity to retain the coded signals corresponding to a transmission delay time.
As can be appreciated from the above description, synchronization between the internal decoder and the external decoder requires a buffer memory therebetween, which inconveniently increases the size of the apparatus.
SUMMARY OF THE INVENTION
According to one aspect of the invention, an audio decoding device includes a coded information memory section for storing coded audio information; an information transmission section for reading the coded audio information stored at an arbitrary position in the coded information memory section; and an audio decoding section for decoding the coded audio information read by the information transmission section and outputting the resultant audio information in accordance with a time axis.
In one embodiment of the invention, the information transmission section includes a buffer memory for retaining an address of an actual pointer for reading the coded audio information in the coded information memory section so as not to be reread, an address of a temporary pointer for reading the coded audio information in the coded information memory section so as to be reread, actual pointer data read by the actual pointer, and temporary pointer data read by the temporary pointer.
In one embodiment of the invention, the actual pointer allows the coded audio information input before the coded audio information pointed by the actual pointer to be erased from the coded information memory section.
In one embodiment of the invention, the actual pointer points a reading position of the coded audio information input after the coded audio information pointed by the actual pointer, to the coded information memory section.
In one embodiment of the invention, in the case where the coded audio information is to be decoded in the order of being input to the
Fujita Takeshi
Ishito Tukuru
Katayama Takashi
Kawamura Akihisa
Matsumoto Masaharu
Renner Otto Boisselle & Sklar
{haeck over (S)}mits T{overscore (a)}livaldis Ivars
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