Pulse or digital communications – Synchronizers – Phase displacement – slip or jitter correction
Reexamination Certificate
1998-05-01
2001-01-09
Pham, Chi H. (Department: 2731)
Pulse or digital communications
Synchronizers
Phase displacement, slip or jitter correction
C704S500000
Reexamination Certificate
active
06173024
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to a bit stream reproducing apparatus used to transfer audio data with employment of a digital leased line.
Since digital signal processing techniques are greatly advanced in which after either analog video signals or analog audio signals have been quantization-coded, signal process operations are carried out, it is easily possible to perform signal process operations of analog information. In particular, since information amounts of audio signals are small, as compared with those of video signals, signal process amounts of the audio signals per unit time required to decode the quantization-coded audio signals so as to obtain original analog audio signals are small. Therefore, these quantization-coded audio signals may be processed by way of digital signal processors and the like.
To effectively transfer information contained in digital video/audio signals, the entire digital video/audio data are subdivided into preselected amounts of digital video/audio data which will then be transferred. Moreover, since this information is compressed, the data transfer in the low rate can be realized. In particular, as to audio data, the data compressing/expanding methods such as “Moving Picture Experts Group (will be referred to as an “MPEG” hereinafter)” established in ISO/IEC SC29/WG where the data compressing/expanding method is standardized by ISO/IEC 11172-3, and this rule is standardized have been widely used in audio transfers, digital satellite broadcasting systems, and DVD with employment of digital leased lines.
As one example of bit stream data, there is an MPEG audio bit stream in which audio data which has been processed by a quantization-coding process operation and thereafter by a compression-coding process operation, quantization-coding information indicative of a quantization-coding method for this audio data, and also compression-coding information indicative of a compression-coding method for the audio data are subdivided into a plurality of packet data, and synchronization data representative of a starting position thereof is added thereto.
FIG. 7A
is a diagram for representing a data structure of an MPEG audio bit stream. Audio Access Units (will be referred to as an “AAU” hereinafter)
100
are transferred one by one in a time sequential manner in unit of packet data reproducible as audio data. In the case of MPEG 1 audio layer 1, assuming now that a sampling frequency is selected to be Fs(KHz), AAU is defined as follows:
AAU(1 frame)=(384×bit rate)/Fs[bit].
In the case of MPEG1 audio layer 2, AAU is defined as follows:
AAU(1 frame)=(
1125×bit rate)/Fs[bit].
As represented in
FIG. 7B
, the AAU
100
of this MPEG1 audio layer 1 is arranged by a 32-bit header
101
, a 16-bit CRC
102
, audio data
103
whose length is variable by a bit rate, and ancillary data
104
. In the case of MPEG1 audio layer 1, as indicated in
FIG. 7C
, the audio data
103
is arranged by bit allocation information
106
, a scale factor
107
, and audio sample data (0 to 11)
14
D.
Also, in the case of MPEG1 audio layer 2, as indicated in
FIG. 8
, the audio data
103
is arranged by bit allocation information
106
, scale factor selection information
120
, a scale factor
107
, and audio sample data (0 to 11)
140
.
Furthermore, the header
101
indicated in
FIG. 7C
is arranged by a 12-bit syncword
109
, various information ID
110
, a layer
111
, a protection bit
112
, a bit rate index
113
, a sampling frequency
114
, and the like, as shown in FIG.
7
D.
Normally, in order that not only bit stream data, but also the MPEG audio bit stream are detected to be dataprocessed, the following process operation is carried out.
That is, the header
101
is provided at a head of detection data, into which a sync signal having a specific value is inserted, and when this sync signal is detected, the data detection is commenced.
The 16-bit data CRC
102
shown in
FIG. 7C
corresponds to error checking data. Since this data CRC is decoded, a quality of transferred data (to check whether or not there is a failure, e.g., data changes occurred in data transfer operation) can be checked.
FIG. 9
is a block diagram for indicating a conventional bit stream reproducing apparatus for the MPEG audio bit stream. In this drawing, reference numeral
201
shows a syncword detector, reference numeral
220
indicates a buffer, and reference numeral
202
denotes a CRC checking circuit. Also, reference numeral
203
represents a bit stream dividing device, reference numeral
204
shows a side information decoder, reference numeral
205
indicates a dequantizing device, reference numeral
206
is a denormalizing device, and reference numeral
207
denotes a sub-band combiner. The buffer
220
, and the above-described circuits
202
to
207
constitute a bit stream decoder
210
.
Next, a signal flow will now be simply explained.
The MPEG audio bit stream is inputted to the syncword detector
201
by which the syncword
109
is detected. In the case that the syncword
109
is detected, since the data starting position of the AAU
100
is determined, the data subsequent to the syncword
109
contained in the header
101
are detected.
Next, after all of the information contained in the header
101
have been detected by the syncword detector
201
, a predetermined amount of data is stored into the buffer
220
. The data outputted from the buffer
220
is CRC-checked by the CRC checking circuit
202
. It should be noted that since the CRC data is optional in the MPEG audio bit stream, only when the protection bit
112
contained in the header
101
is equal to “1”, the CRC data
102
is added.
The data outputted from the CRC checking circuit
202
is entered into the bit stream dividing device
203
. This bit stream dividing device
203
divides the inputted data into each of information units such as bit allocation information
106
, scale factor
107
, and audio sample data
140
. In particular, both the bit allocation information
106
and the scale factor
107
are outputted to the side information decoder
204
.
In the side information decoder
204
, both the bit allocation information
106
and the scale factor
107
which correspond to the side information are decoded to produce bit numbers, namely bit allocation data for determining a data length of each of audio samples, and also a scale factor corresponding to a coefficient value used in a calculation for this bit allocation. These bit numbers are allocated to each of the audio samples during the dequantizing operation. Then, these bit numbers and scale factors are sent out to the dequantizing device
205
and the denormalizing device
206
.
In the dequantizing device
205
, the audio data samples
140
are dequantized based upon the output data (namely, information such as quantizing bit number) from the side information decoder
204
. The denormalizing device
206
multiplies the output derived from the dequantizing device
205
by the scale factors entered from the side information decoder
204
. Since the MPEG audio data is divided into
32
audio subdata by the highspeed Fourier transform during the coding operation, the calculation results of the denormalizing device
206
are recombined with each other by the sub-band combiner
207
to thereby produce the original digital audio signal.
Since the conventional bit stream reproducing apparatus is arranged in the above-described manner, in such a case that the bit allocation information
106
corresponding to partial data contained in the inputted MPEG bit stream signal could not be correctly transferred due to occurrences of the transfer noise, the data length of the subsequently transferred audio sample data
140
and the data starting position of the audio sample data to be dequantized are erroneously recognized. As a result, there is a problem that acoustic noise may occur.
Also, in such a case that the inputted MPEG bit stream signal could not be correctly transferred due to noise, for instanc
Kumano Makoto
Kuroda Masashi
Nanba Takahiro
Corrielus Jean B.
Mitsubishi Denki & Kabushiki Kaisha
Pham Chi H.
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