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BACKGROUND OF THE INVENTION
1. Field the Invention
This invention relates generally to digital disc playback apparatus for use
with a digital disc on which two-channel digital audio signals are
recorded and, more specifically, to digital disc playback apparatus in
which digital data other then audio signals are recorded and utilized upon
playback.
2. Description of the Prior Art
The system employing an optically encoded digital audio disc, which has
become known as a compact audio disc or a digital audio disc, is known to
reproduce high quality stereophonic musical signals. In such systems, the
data is recorded by a laser as pits in the surface of the disc and then
the information encoded in the pits is read out by another laser device in
the playback system. At present only audio information has been encoded on
such discs, however, it is apparent that if information or data
representing characters, display data, program data, and data other than
conventional stereophonic audio signals could be reproduced by such
optical digital audio disc system, without extensive modifications to the
existing player, a large range of applications would be possible for the
compact digital disc system. For example, some desired uses might involve
playback apparatus to reproduce visual information such as charts,
statistics, graphs, and the like, as well as pictural illustrations, still
pictures, or video games, by adding only a suitable display unit to the
playback apparatus. This would then provide a wide range of applications
for the compact digital disc system.
Nevertheless, while these uses for the compact digital disc system other
than audio signals might be obtained by a flexible magnetic disc or
"floppy" disc formed on relatively thin plastic base material, the data
memory capacity currently provided in the compact audio disc is around 500
megabytes and this is much greater than the memory available on the
standard flexible disc.
On the other hand, because compact audio discs have been developed and
utilized principally for the reproduction of audio signals, the search
capability is relatively coarse, since the informational units are
relatively large musical program segments. That is, the data on the disc
is searched on a relatively large scale basis since the musical program
segments represent large informational units. This is in conflict,
however, with requirements relative to data uses other than audio, since
these other data uses involve data segments that must be read out and
identified on a much smaller unit basis, for example, on the order of 128
bytes to 10 kilobytes. This presents a distinct problem in attempting to
use the compact digital disc system for purposes other than the
recordation and replaying of high quality stereophonic audio signals.
Additionally, in the case of musical signals the degree of accuracy
required for searching for the beginning of a music program may be kept
within such a low range that no problem will be caused in terms of the
reproduced audio signal if the search yields somewhat erroneous results.
Therefore, the audio data in the main channel which was separated from the
signal reproduced from the compact disc can be written once into a buffer
memory and then be subjected to error correction processing and, at the
same time, variations in the time base in the data can be eliminated.
Nevertheless, the time base variation of a subcoding signal was not
eliminated to reduce the costs of manufacturing, because fine or accurate
searching is not required. Consequently, if it is attempted to utilize the
compact digital disc playback apparatus as a data memory, the problem is
presented such that it is impossible to correctly specify, with any
accuracy, the read address by use of the subcoding signal.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a disc
playback system for playing back digital data other than audio signals,
which can eliminate the above-noted defects inherent in the prior art.
Another object of the present invention is provide a compact digital disc
playback apparatus that can read out digital signals of program data or
the like in place of digital audio signals utilizing a compact disc of the
kind used for standard digital audio playback.
In accordance with an aspect of the present invention, a disc playback
system is provided that employs a write clock generator that generates a
write clock signal that is synchronized with a signal reproduced from the
compact disc and also a read-out clock generator that generates a clock
signal having a fixed period. A buffer memory is provided in which the
main digital data signal reproduced from the disc is written by the use of
the write clock signal and from which the main digital data signal having
been written therein is read out by use of the read-out clock signal. A
second buffer memory is provided in which the subdigital data reproduced
from the disc is written by use of the write clock signal and from which
the subdigital data written therein is read out by means of the read-out
clock signal. The present invention further provides a control system that
searches a playback location in the main digital data by using the
subdigital data that has been read out from the second buffer memory.
The above, and other objects, features, and advantages of the present
invention will become apparent from the following detailed description of
illustrative embodiments thereof to be read on conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the data arrangement of recording
data on a compact disc to which the present invention is applied;
FIG. 2 is a schematic representation of the data of FIG. 1 having been
rearranged in a parallel fashion;
FIG. 3 is a schematic representation showing the arrangement of one BLOCK
upon recording the digital data in an embodiment according to the present
invention;
FIG. 4 is a block diagram of one embodiment of digital disc playback
apparatus according to the present invention;
FIG. 5 is a schematic representation of a word format of the serial data
according to one embodiment of this invention;
FIG. 6 is a schematic representation of the arrangement of the subcoding
signal according to another embodiment of the present invention;
FIG. 7 is a block diagram showing an embodiment of an error correction
encoder for the subcoding signal of the present invention;
FIG. 8 is a block diagram of an embodiment of an error correction decoder
for the subcoding signal to the present invention;
FIG. 9 is a schematic representation showing the timing relationships and
contents of the subcoding signal and the data in the main channel with
respect to recording processing according to the present invention; and
FIG. 10 is a schematic representation showing the timing relationships and
contents of the subcoding signal and the data in the main channel with
respect to the reproducing processing according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention is directed to a compact disc of the kind typically
employed to record stereophonic audio signals, and FIGS. 1 and 2 show the
data arrangement of the signals to be recorded on a compact disc. More
specifically, in FIG. 1, a data stream as recorded on a compact disc is
represented consisting of 588 bits of record data with each FRAME having
at its head or beginning a frame sync pulse group FS having a specific bit
pattern. After the frame sync pulses FS are arranged 3-bits of DC
restoration bits RB. Following the initial 3-bit DC restoration bits RB
there are arranged the 0th to 32nd data bit groups DB, each comprising 14
bits per group, with the 3-bit DC restoration bits RB being alternately
recorded so that the data bits DB are arranged therebetween. The 0th bits
among these data bits DB are called the subcoding signal or user bits and
are used to control the playback of the disc and to display information
relating thereto, such as the program segment number of the like.
Thereafter, the 1st-12th and 17th-28th data bit groups DB are provided for
audio data in the main channel. The remaining 13th-16th and 29th-32 nd
data bit groups DB are assigned as parity bits utilized in the error
correction coding in the main channel. Each of the data bit groups DB
consists of 14 bits, which have been derived by converting the 8-bit data
into 14 bits utilizing the known 8-14 conversion process during recording.
Referring now to FIG. 2, one BLOCK is shown consisting of 98 FRAMES that
are arranged sequentially in parallel, wherein each of the data bit groups
DB is represented by 8 bits and the DC restriction bits are excluded. In
the 0th and 1st frames the subcoding signals P-W in the 0th data group DB
form sync patterns having predetermined bit arrangements. More
specifically, in the Q channel, the cyclic recirculating code (CRC) for
error detection and correction is inserted in the last 16 FRAMEs of the 98
FRAMEs making up the BLOCK shown in FIG. 2.
The P channel contains a signal that is a flag to indicate a music program
and to indicate a pause, and this signal has a lower level during the
extent of a musical program and a higher level during the extent of a
pause. The P channel signal also contains a 2-Hz period during the lead
out from a music program segment. It is possible to select and playback a
specified musical program by detecting and counting this signal in the P
channel. Similarly , the Q channel enables a more complicated and
sophisticated control of this kind, for example, when the Q-channel
information is stored in a microcomputer provided in the disc playback
apparatus, it is possible to shift quickly from one musical program to
another during the playback of a music program. Thus, respective ones of
the recorded musical programs may be selected and played back at random,
that is, out of the order at which they appear on the disc. The other
channels R through W can be used to indicate or explain by audible vocal
sounds information concerning the author or composer or to recite poetry
or the like relative to the musical programs recorded on the disc.
Among the 98 bits in the Q channel of one BLOCK, the first two bits are
used to provide a sync pattern as discussed above and the subsequent four
bits are used as address bits. Following the address bits the 72 bits are
used as data bits and finally the CRC code having 6 bits is added at the
end for error detection and correction. A track number code TNR and an
index code X are included in the 72 bits representing the data bits and
the index code and the track number code can be represented by two decimal
codes that can vary from 00 to 99. Additionally, also included in the Q
channel data is a time indication code representing the duration of the
various music programs and of the pauses, and a time indication code
indicating the absolute time duration or elapsed time that continuously
changes from the beginning to the end of the compact disc. It should be
noted that in the compact disc the beginning of the program material is at
the inner most radius and the end of the program material is at the outer
most radius, a situation contrary to conventional phonograph records.
These time indication codes comprise the codes indicating the minute,
second, and FRAME, each consisting of two decimals, providing information
concerning the data on the digital disc. According to this system, one
second is divided into 75 FRAMEs to form the time scale and, in order to
access the compact disc to obtain digital data on a shorter unit basis
than the music segments, the time indication code with respect to the
above-described absolute time duration is used, that is, the time code
that indicates elapsed time on the disc.
According to the above description, it is seen that a minimum unit of
change of the subcoding signal for the compact digital disc is 98 FRAMEs.
In this embodiment, when recording digital signals other than stereophonic
musical signals, which digital signals are shown for example in FIG. 3,
one BLOCK is formed having a length of 98 FRAMEs corresponding to the 0th
to 97th FRAMEs of FIG. 3. As pointed out hereinabove, one FRAME includes
digital audio data consisting of 12 words, so that 24-bit digital data can
be inserted in one FRAME. Note the 12 words are from the 1st-12th and
17th-28th data bit groups DB. Turning then to FIG. 3, one ROW contains a
total of 32 bits of one sample in the left channel (L) of the audio data
and 32 bits of one sample in the right channel (R) thereof, and each FRAME
consists of 6 such ROWs. This is represented also in FIG. 2 in the data
portions DB(1-32), which is formed of six samples that is six ROWs, of 32
bits for each of the left and right channels.
A 1-bit sync bit is placed at the beginning of each 32 bit ROW and in the
0th FRAME the first two ROWs are begun with a 0 value in the sync bit
position. According to the present invention, the sync bits appearing at
the first bit position of the first ROW of all of the even-numbered frames
have a "0" value, whereas the sync bits commencing the first 32 bits in
all frames odd-numbered have a "1" value. These sync bits enable the
detection of the head location of the block on a 98 FRAME unit basis
because of the two successive "0" bits in the first and second ROWs of the
first FRAME of the BLOCK.
According to the present invention, the above-described BLOCK consist of
2352 bytes (24 bytes.times.98 FRAMES) and so when the data of two
kilobytes (2048 bytes) is inserted in one BLOCK, then 304 bytes (2432
bits) will remain. There are then provided the remaining 588 bits
(6.times.98) that are used as sync bits, and a 7-bit mode signal and a
24-bit address signal are inserted in the first 32 bits in the 0th FRAME.
Thus, 1813 bits still remain in one BLOCK according to the present
invention, and these 1813 bits can be assigned to redundant bits when the
error correction coding processing is performed for the data of one BLOCK.
The 7-bit mode signal in FIG. 3 serves to specify the kind of data
contained within each BLOCK, for example, the mode signal can be used to
discriminate character data, still picture data, and program code
information, and the 24-bit address signals serve to specify the data in
that BLOCK. Furthermore, by setting the sync bits of even-numbered FRAMEs
to "0" the present invention provides an arrangement of a data BLOCK on a
2-FRAME unit basis. Thus, for the BLOCK having a size of two FRAMEs, a
mode signal and an address signal are added to each BLOCK. In the case of
a BLOCK having a length of 98 FRAMES, as discussed hereinabove, the codes
for indicating the absolute time durations of the P data and the Q data of
the subcoding signals in the same BLOCK are identical.
Accordingly, digital signals in the format shown in FIG. 3 can be recorded
on a compact disc in the same fashion as on an audio compact disc, that
is, a digital signal to be recorded is fed to a digital input terminal of
a digital audio processor and this digital signal is converted into a
video signal format. Such video signal format digital signal is then
recorded using a video tape recorder (VTR) of the conventional rotary head
kind. In this case, table of contents (TOC) data used to generate a
subcoding signal is preliminarily recorded in the audio track on the
starting edge section on a magnetic tape on which the above-described
digital signal is to be recorded. The table of contents data reproduced
from the magnetic tape is then supplied to a subcoding generator, and the
reproduced digital signal is fed to an encoder and the subcoding signal is
also supplied to the encoder. A laser beam is then modulated in response
to the output signal of the encoder, and a master compact disc is formed
by this modulated laser beam.
Another method of recording a digital signal could also be followed in
which a hard-disc memory, which can be accessed at high speed, is accessed
by a minicomputer and a digital signal is then fed in real time to an
encoder of the compact audio disc cutting system.
When recording the digital signal, because the time indication codes, which
consist of each column representing minute, second and FRAME, that are
included in the Q channel of the subcoding signal are used as addresses,
the corresponding relationships between such addresses and the digital
signals must be determined. More specifically, because the digital signal
in the main channel is recorded on the master disc through the use of an
encoder for the CRC codes, which consists of the combination of two
interleave series and the Reed-Solomon code, the recording position on the
disc of one data BLOCK, consisting of data of 98 FRAMES, as represented in
FIG. 3, then locates a predetermined position. On the other hand, the time
indication code signals included in the Q channel of the subcoding signal
is a continuous coding signal such that the column of the FRAMEs will
change on a 98-FRAME unit basis in the track on the disc, and when the
column totals 75 FRAMEs, the number in the seconds column will change and,
accordingly, when this number in the seconds column reaches 60 seconds,
the minutes column will change. As described above, the continuous time
indication code changes continuously from the first section in the program
area of the disc to the end of the lead-out track of the program area and,
consequently, it can be used as an address for the digital signal to be
recorded in the predetermined location.
FIG. 4 represents one embodiment of the present invention in which a
compact disc 1 has a digital signal of the above-described format recorded
thereon in a spiral record track. Compact disc 1 is rotated by spindle
motor 2 that is controlled by spindle servo circuit 3, so that compact
disc 1 rotates at a constant linear velocity but with a varying angular
velocity. Optical head 4 employs a laser source for generating a laser
beam to pick up of the information from compact disc 1, and optical head 4
typically includes an objective lens and a photo receiving device for
receiving the laser beam reflected from compact disc 1. Optical head 4 can
be moved radially along compact disc 1 by a motor and threaded shaft 5,
which comprises a lead screw that is rotated by the motor along which a
threaded nut attached to the head 4 travels. Thread feed motor 5 is
controlled and driven by thread drive circuit 6. Optical head 4 can be
deflected both in the direction perpendicular to the signal surface, that
is, the surface of compact disc 1, and also in the direction parallel
thereto and is controlled so that the focusing and tracking operations by
the laser beam upon playback are always properly performed. To accomplish
such focussing and tracking, focus servo circuit 7 and tracking servo
circuit 8 are provided.
The signal reproduced by optical head 4 is fed to RF amplifier 9, and
optical head 4 is typically provided with a focus error detection section
consisting of the combination of a cylindrical lens with a four-segment
detector and a tracking error detection section employing three laser
spots. The output data signals of RF amplifier 9 are fed to clock
extraction circuit 10 that provides outputs on two separate lines
representing the data with the clock signal extracted therefrom and the
clock signal, and these signals are fed to frame sync detection circuit
11.
In this embodiment, the digital signal recorded on compact disc 1 has been
modulated according to the EFM system, EFM being a known method of block
converting 8-bit data into data of a greater number of bits, preferably 14
bits, and in this case 14 bits provide a long minimum inverting time
period of the modulated signal in order to reduce low frequency
components. Accordingly, digital demodulator 12 is arranged to provide EFM
demodulation of the reproduced signal. The bit clock signal which is
extracted by clock extraction circuit 10 and the frame sync signal that is
detected by frame sync detection circuit 11 are fed to the spindle servo
circuit 3.
The subcoding signal is separated by the digital demodulator 12 and this
separated subcoding signal is fed through buffer memory 13 to system
controller 14, which is equipped with a central processing unit (CPU), not
shown. The rotation operation of compact disc 1, the thread feeding
operation and the reading operation of the optical disc 4, and other
similar system operations are controlled by system controller 14. Control
commands are supplied to system controller 14 through interface unit 19,
which is of the conventional kind, and the reading operation of the
desired digital signal from compact disc 1 using the subcoding signal is
controlled by system controller 14.
The main digital data output from digital demodulator 12 is supplied to
random access memory (RAM) controller 15, to random access memory (RAM)
16, and to error correction circuit 17. Signal processing necessary to
eliminate variations in the time base of the data and error correction and
error interpolation are carried out in RAM controller 15, RAM 16, and
error correction circuit 17, so that corrected main digital data is
provided at the outputs of RAM controller 15. In the system in which audio
information has been recorded on compact disc 1, during playback
digital-to-analog converters would be connected to the outputs of RAM
controller 15, however, in the embodiment of FIG. 4 no digital-to-analog
converter is necessary, because the signal is already in digital form at
the outputs of RAM controller 15. This reproduced digital data signal is
fed directly to data conversion unit 18, which may comprise a
parallel-to-serial converter. Also, the reproduced subcoding signal
supplied from buffer memory 13 is fed to data conversion unit 18, and the
reproduced data is converted into serial form therein. This reproduced
serial data signal is fed to interface unit 19, and the data for system
controller 14 is supplied from microcomputer system 20 through interface
unit 19 to system controller 14. Microcomputer system 20 specifies a
read-out address and applies drive control signals, such as start signals,
in addition to the read-out addresses to interface 19 and system
controller 14.
An example of the word format used in the serial output signal produced by
data conversion unit 18 is shown in FIG. 5. In this serial signal, one
word consists of 32 bits with the first four bits being used as a
preamble, the next four bits being used as auxiliary bits for the audio
data, and the next twenty bits being used for the actual digital audio
sample. In the case where the digital audio sample consists of only
sixteen bits, the sixteen bits are inserted starting at the end closer to
the auxiliary bits, that is, at the least significant bit (LSB) position.
Finally, following the 20 bits of the digital audio sample there are added
four additional bits in which bit V is a flag indicating whether the
digital audio sample of that word is effective or not, bit U is a bit of
the subcoding signal, bit C is an identification bit used to identify the
channel, and bit P is a parity bit. Bit U of the subcoding signal is
inserted into each word format, 1 bit at a time, and these inserted bits
are sequentially transmitted upon reproduction.
In one embodiment of the present invention, the time base variation of the
subcoding signal is eliminated by buffer memory 13. This time base
correction is the same as that executed by RAM controller 15 and RAM 16,
with respect to the actual digital signal in the main channel. More
specifically, RAM controller 15 produces a write clock signal synchronized
with the reproduction signal from a detected frame sync signal and writes
the digital data into RAM 16 by the use of this write clock. Thus, when
the digital signal is read out from RAM 16 the read clock produced from an
output of a quartz crystal oscillator 15a is utilized. The present
invention teaches that these write clock and read clock signals are used
to write and read out, respectively, the subcoding signal into and from
buffer memory 13. Thus, the subcoded signal read out from buffer member 13
does not have time base variations, so that there are no changes in the
timing relationship between the digital signal and the main channel and
the subcoding signal that might be due to such time base variations.
According to an embodiment of the present invention, a read instruction to
a predetermined address is first executed by microcomputer system 20 and
this address is a code that indicates an absolute time duration in the Q
channel and is supplied through interface unit 19 to system controller 14.
Following this coded address signal, system controller 14 controls thread
drive circuit 6 to move optical head 4 to the location near a desired
pick-up location, while at the same time supervising or monitoring the
subcoding signal being reproduced by optical head 4. In this example,
reproduction is started from a location spaced a few BLOCKs away from the
desired pick-up location to prevent the situation in which a malfunction
in the access operation remains because an error was included in the
reproduced subcoding signal and the set subcoding signal is not
reproduced. The desired BLOCK is then obtained by either method of
detecting the coincidence of the reproduced subcoding signal with the
designated address or by starting the playback from a known location near
the correct subcoding signal and then counting the frame sync signals.
In another embodiment differing from the above, it may be possible to
insert the address code signal at which the error correction code was
coded in the R-W channels of the subcoding signals. In that regard,
another embodiment of the invention is described hereinbelow in which the
address code signal is inserted in the R-W channels of the subcoding
signals. In such case, one PACKET consists of the 96-FRAME data excluding
the sync pattern of the 0th and 1st FRAMEs and excluding the P and Q
channels in the one BLOCK consisting of 98 FRAMEs as shown in FIG. 2. This
embodiment is represented in FIG. 6, in which a PACKET of 6.times.96 bits
is further divided into four PACKs, each having 24 SYMBOLs. Twenty SYMBOLs
of each PACK are used for address data and the remaining four SYMBOLs are
parity bits of the error correction code of each PACK. A Reed-Solomon code
(24,20) is used as an error correction code for this pack of (6.times.24)
bits. This Reed-Solomon code can be represented by a polynomial as follows
P(X)=(X.sup.6 +X+1)
over the Galois field GF(2.sup.6).
This Reed-Solomon code including the four P-parity SYMBOLs can correct one
SYMBOL error and two SYMBOL errors and can detect three or more SYMBOL
errors.
An error correction encoder is represented at 30 in FIG. 7 with respect to
the R-W channels as described above, and error correction encoder 30
employs a P-parity generator, represented by the broken line 31, of the
previously mentioned (24,20) Reed-Solomon code, and also includes
interleaving circuit 32. Twenty input symbols 33 in the same PACK are fed
to P-parity generator 31 to generate four parity symbols P.sub.0,P.sub.1,
P.sub.2, and P.sub.3. The 24 symbols to be output from P-parity generator
31 are supplied to interleaving circuit 32, which is constructed employing
a random access memory (RAM) and including an address controller, and
which generates the output data to which a predetermined delay time value
has been added to each SYMBOL of input data by controlling the write
addresses and the read addresses.
As shown in FIG. 7, in place of the actual RAM the means for adding the
predetermined delay time value to each SYMBOL is represented by a
plurality of delay elements, in order to simplify understanding of the
interleaving circuit and to simplify the drawing thereof. There are three
delay elements that provide a delay time of one PACK (24 SYMBOLs), three
delay elements that provide a delay time of two PACKs, three delay
elements that provide a delay time of three PACKs, three delay elements
that provide a delay time of four PACKs, three delay elements that provide
a delay time of five packs, three delay elements that provide a delay time
of six PACKs, and three delay elements that provide a delay time of seven
PACKs. The delay time value of the SYMBOL in which no delay element is
seen to be inserted is thus set to zero. Accordingly, three combinations,
each consisting of eight different kinds of delay time values, from zero
to seven PACKs are provided. An output SYMBOL 34 of one PACK is generated
from interleave circuit 32.
FIG. 8 represents error correction decoder 40, again with respect to
channels R-W, in which deinterleaving circuit 42 has applied thereto 24
SYMBOLs, shown generally at 41 as one PACK of the reproduced subcoding
signals. Parity or P-decoder 43 for the (24,20) Reed-Solomon code is
provided with the output from deinterleaving circuit 42. It is noted that
the input data 41 to the deinterleaving circuit 42 corresponds to the
output data 34 from interleaving circuit 32 of FIG. 7. The deinterleave
processing is performed so that data time values given by the interleaving
circuit 32 are cancelled, and each SYMBOL has then the delay time values
of 7 PACKs. While the decoder of FIG. 8 is shown having discrete time
delay elements in each line, in fact, deinterleaving is performed by
controlling the write addressing and the read addressing in a random
access memory. Nevertheless, in FIG. 8, deinterleaving circuit 42 is shown
in one construction in which delay elements have predetermined time delay
values as represented by the numerical values shown therein and as
arranged in the transmission lines of each respective SYMBOL. Delay
elements of 7 PACKs are inserted into the transmission lines of the SYMBOL
having the delay value of zero in the interleaving circuit 32 and
similarly, delay elements of 6,5,4,3,2 and 1 PACKs are inserted
respectively into the transmission lines of SYMBOLs having delay time
values of 1,2,3,4,5 and 6 PACKs in interleaving circuit 32 of FIG. 7.
Again, no delay element is inserted into the transmission line of the
SYMBOL having the delay time value of 7 PACKs in the interleaving circuit
32.
Parity decoder 43 has a syndrome generator (not shown), to generate four
error syndromes by calculating H.sub.p .times.V.sub.p, wherein H.sub.p is
a parity check matrix, and V.sub.p is a reproduction data matrix, in the
known fashion. Checking of these four error syndromes then enables the
detection of one-SYMBOL error, two-SYMBOL error and three or-more SYMBOL
error, and by obtaining the error locations of the one-SYMBOL error and
two-SYMBOL error, these errors can be corrected. Therefore, as the output
of P-decoder 43 an error corrected output data signal 44 is obtained.
Another arrangement is possible in which a complete type interleave
processing is employed, whereby the SYMBOLs in a plurality of PACKs are
written into the RAM and the above-described SYMBOLs in a plurality of
PACKs are then read out from the RAM using the read addresses in a
sequence different from the change in the write addresses.
FIG. 9 represents the timing relationship between the sub-coding signal and
the main channel when recording on a master disc. Input SYMBOL 33
consisting of 20 SYMBOLs is supplied to the above-described error
correction encoder 30 and a reference character SSY represents the
sub-code sync representative of the timing relationship of the zero and
first FRAMEs among the 98 FRAMEs, in which the sync pattern of the
sub-coding signal is included. The 20 SYMBOLs in the R-W channels that are
included, respectively, in the second through twenty-first FRAMEs of the
98 FRAMEs in the BLOCK following the sub-code sync signal SSY correspond
to input SYMBOL 33.
This input SYMBOL 33 contains SYMBOLs that are indicated b
S.sub.0n,S.sub.n+1,S.sub.2n2, . . . , S.sub.18n+18 and S.sub.19n+19. The
suffixes sequentially change in increasing integers as 0,1, 2, . . .
18,19, and indicate the SYMBOL number in one PACK. The suffix that
sequentially changes as n,n+1, . . . n+18,n+19, represents the number of
the FRAME in which each SYMBOL is included. In FIG. 9, the nth FRAME in
the main channel 35 indicates data W.sub.0A,n,W.sub.0B,n,W.sub.11A,n, . .
. W.sub.11A,n,W.sub.11B,n of 25 SYMBOLs that are included in one FRAME,
that is, the nth FRAME in the main channel. Note that one SYMBOL consists
of eight bits. More specifically, the input SYMBOL 33 of the sub-coding
signal and the data signal 35 in the main channel shown in FIG. 9 are the
data in the nth FRAME at the stage before they are encoded.
Input SYMBOL 33 is supplied to error correction encoder 30, as described
hereinabove, so that output SYMBOL 34 of one PACK is generated. This
output SYMBOL 34 exhibits the actual SYMBOL in the case where the
interleaving circuit 32 of the error correction encoder 30 is formed by
use of a random access memory and a random access memory control unit. If
the interleaving circuit is comprised of a memory, then the delay time
corresponding to two PACKs will be imparted because the data of one PACK
is stored first in the memory and then this is read out, thereby to
perform the interleave processing. The result of this is that a delay time
of two PACKs is added to the delay time value as shown in FIG. 7, for
example, and the SYMBOL S.sub.0n-2.times.24 (-2) is generated from the
error correction encoder 30 in response to SYMBOL S.sub.0n in the input
signal 33.
The suffix (2) in the subscript of such SYMBOL means that the subcode sync
SSY is included in two FRAMEs. This suffix number is set to (-2) for a
delay time value of up to 98 SYMBOLs, is set to (-4) for a delay time
value up to 196 SYMBOLs, and is set to (-6) for a delay time value of up
to 294 SYMBOLs. Data 35 in the nth FRAME in the main channel is fed to
encoder 36 in the min channel and the coding processing of the CIRC code
is performed, in this way, output data 37 consisting of 32 SYMBOLs, which
includes the parity bits P.sub.0, P.sub.1, P.sub.2, and P.sub.3 of one
interleave series and the parity bits Q.sub.0, Q.sub.1, Q.sub.2, and
Q.s | | |
