Method of reproducing high-speed audio data by a CD-ROM player

A method of performing a reproduction of a high-speed audio data in a CD-ROM player comprises the steps of; reading EFM demodulated data from the disk at a high speed, writing the thus read data one after the other into a CD-ROM data storage as an input buffer of an audio signal processing section, reading out the written data at the same frequency as the sampling frequency thereof, transmitting the data read out from the CD-ROM data storage sequentially to the audio signal processing section, stopping the EFM demodulated data writing operation to the CD-ROM data storage when the address for writing the data is on the verge of exceeding the address which is not read out yet, simultaneously jumping the optical disk back for a certain pitch corresponding to a predetermined number of tracks to read in again, and resuming the data writing operation from the point where the data writing was previously stopped when a predetermined number of vacant addresses is made in the CD-ROM data storage by the above data reading operation which has been advanced during the period the data writing operation was stopped.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of reproducing high-speed audio 
data by a CD-ROM player which is capable of reproducing both audio and 
digital data. 
2. Description of the Prior Art 
Hitherto, there has been proposed a CD-ROM and a CD-I (CD-Interactive) as 
an optical disk capable of recording both digital data such as the data 
operable in computers, and video data as well as audio data such as music, 
voice sound and so on. The CD-ROM is a disk standardized for recording 
above explained digital data as well as audio data in the audio signal 
area, yet having compatibility with a CD (compact disk) which basically 
deals with acoustic signals only, whereas the CD-I is an interactive disk 
defined in the Mode-2 of the above-mentioned CD-ROM, and is a standardized 
system in which the above-disclosed computer data, video data, audio data 
and so on are recorded per blocks by a time division multiplex mode. 
FIG. 4 is a signal processing circuit in a conventional CD-ROM player. In 
the figure, reference numeral 1 denotes an audio signal processing 
section, 2 denotes a memory for storing audio signals, 3 an audio 
interface, 4 a digital to analog converter (hereinafter referred to just 
as "D/A converter"), 5 a low pass filter, 6 a CD-ROM data processing 
section, 7 a CD-ROM data storage which is also used as an interface buffer 
memory, and reference numeral 8 denotes a host computer interface such as 
a small computer system interface (hereinafter referred to simply as 
"SCSI"). 
In reference to FIG. 4 the signal which had previously been modulated by 
the EFM (Eight-to-Fourteen Modulation) method and read in from a disk is 
first demodulated at an EFM demodulation circuit (not shown), and then 
sent to the signal processing circuit shown in FIG. 4. The input EFM 
demodulated data is first stored in the memory 2, and then an error check 
to the audio signal is performed by a CIRC (Cross Interleave Reed-Solomon 
Code) error checking method to correct defected audio signal if any in the 
audio signal processing section 1. Thereafter, if the signal read in from 
the disk is an audio signal, the data corrected by the CIRC error checking 
method is fed to the D/A converter 4 by way of the audio interface 3, and 
after the digital to audio conversion thereof is through, it is further 
fed to the low pass filter 5 where high frequency components are deleted, 
so that a reproduced audio signal in the form of an analog signal is 
finally output. 
On the other hand, if the signal read in from the disk is a digital signal, 
the data corrected by the CIRC error checking method is fed to the CD-ROM 
data storage 7 by way of the CD-ROM data processing section 6, wherein an 
error check to the stored CD-ROM data is performed with the error 
correction parity codes P and Q, and after the data is corrected thereby, 
the digital data is fed to the interface 8, which is further sent to a 
host computer. 
By the way, it has been a common procedure nowadays to read in the digital 
data at a twice or a four-time faster speed than the normal speed in order 
to meet with the recent increase in requirement for high-speed data 
processing. However, since it is necessary to reproduce the audio signal 
as a correct sound in case that digital data and audio data are taken in 
by turns from one disk, in a conventional CD-ROM player as the one shown 
in FIG. 4, the audio signal has to be read in at the same speed as the 
sampling frequency thereof. Due to this, it has been a problem to require 
a certain time to switch the rotation speed of the disk any time when the 
signal to be received from the disk is changed from audio to digital and 
vice versa, and therefore there has not been much merit in processing 
digital data at a high speed. 
A simple solution to this problem has been to read in the audio signal at 
the same speed as that for reading the digital data, but has not been 
effective since the conventional CD-ROM player can not make a faithful 
reproduction of the audio signal at a high speed due to a change in the 
reproducing speed. 
SUMMARY OF THE INVENTION 
The present invention has been made to eliminate such problems as described 
above, and it is an object of the present invention to provide a method of 
reproducing audio data in a CD-ROM player, wherein even in a case that 
digital data and audio data are read out by turns from one disk, it is not 
necessary to slow down the rotation speed of the disk for reproducing the 
audio signal. 
In order to achieve the above object, a method of performing a reproduction 
of high-speed audio data in a CD-ROM player according to the present 
invention comprises the steps of; reading EFM demodulated data from the 
disk at a high speed, writing the thus read data one after the other into 
a CD-ROM data storage as an input buffer of an audio signal processing 
section, reading out the written data at the same frequency as the 
sampling frequency thereof, transmitting the data read out from the CD-ROM 
data storage sequentially to the audio signal processing section, stopping 
the EFM demodulated data writing operation to the CD-ROM data storage when 
the address for writing the data is on the verge of exceeding the address 
which is not read out yet, simultaneously jumping the optical disk back 
for a certain pitch corresponding to a predetermined number of tracks to 
read in again, and resuming the data writing operation from the point 
where the data writing was previously stopped when a predetermined number 
of vacant addresses is made in the CD-ROM data storage by the above data 
reading operation which has been advanced during the period the data 
writing operation was stopped. 
As shown in FIG. 4, there is provided, for example, a 4K-byte small 
capacity RAM as an audio signal storage 2 which is enough for error 
correction. On the other hand, a CD-ROM data storage 7 is provided, for 
example, with 128K-byte large capacity RAM since it also functions as a 
buffer memory for data transmission to a host computer (not shown). 
Further, the CD-ROM data storage 7 in a conventional CD-ROM player is used 
only for reproducing digital data such as computer data, video data and so 
on, and is not used for reproducing audio data such as music, vocal sound 
and so forth. 
The present invention has been made paying attention to this fact, wherein 
a CD-ROM data storage 7 which was not conventionally used except for 
reproduction of digital data is used for reproduction of audio data as an 
input buffer memory of the audio signal processing section 1. 
In other words, according to the present invention, the EFM demodulated 
data read in at a high speed is once written into the CD-ROM data storage 
7 instead of directly being fed to the audio signal processing section 1, 
and thereafter, the thus written EFM demodulated data is read out one by 
one from the CD-ROM data storage 7 at the normal speed which is the same 
speed as the sampling frequency of the audio signal so as to be 
transmitted to the audio signal processing section. 
By this method above, audio and video signals can both be taken in at twice 
or faster than the normal speed, so that even in a case for reading in 
audio and digital data by turns from a disk, it is no longer necessary to 
slow down the rotation speed when reading in audio data to the original 
speed. 
On the other hand, when the demodulated data read in at twice or four times 
faster than the normal speed is written into the CD-ROM data storage 7, 
considering the fact that the speed for reading out the audio signal 
therefrom is the normal speed which is same as the sampling frequency 
thereof, there will be a moment at which the speed of the writing 
operation exceeds that of the reading operation, so that the EFM data 
which has been stored in the CD-ROM data storage but has not been read out 
yet to be reproduced can be destroyed. 
In order to avoid this phenomenon, in the present invention, when all the 
addresses in the CD-ROM data storage are filled with the EFM data, and the 
writing operation turns round to reach the address which has not been read 
out yet, the data writing operation is stopped, although during which time 
the reading operation is still continued, and simultaneously the optical 
pick up device is jumped back for a predetermined number of tracks to read 
in the data from the disk again, and thereafter, when a predetermined 
number of addresses available to write in is made in the CD-ROM data 
storage by the still continued data reading operation, the writing 
operation of the demodulated data is resumed from the address at which it 
had previously been stopped. 
With the control operation above, the demodulated data read in at a high 
speed from the disk is written into the CD-ROM data storage one by one 
without destroying the EFM demodulated data which has not been read out 
therefrom yet. It is to be noted that for a smooth operation of the above 
controlling process, it will be preferable to perform the writing 
operation of the EFM demodulated data to the CD-ROM data storage and the 
stopping operation thereof per block (or sub code) of the CD format. 
Other objects and features of the invention will be more fully understood 
from the following detailed description and appended claims when taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following, several embodiments of the present invention are 
described with reference to the accompanying drawings, wherein FIG. 1 is a 
block diagram showing one embodiment of the CD-ROM player adopting the 
method of the present invention. It is to be noted that like reference 
numerals in FIG. 4 denote like or corresponding portions in FIG. 1. 
Referring to FIG. 1, reference numeral 1 denotes an audio signal processing 
section, 2 denotes a memory for audio signals, 3 an audio interface, 4 a 
D/A converter, 5 low pass filter, 6 a CD-ROM data processing section, 7 a 
CD-ROM data storage which is also used as an interface buffer memory, and 
8 denotes a host computer interface such as SCSI. 
The audio signal processing section 1 is connected at the input terminal 
thereof to an audio buffer controller 10 through a selector 9, wherein the 
audio buffer controller is selectively connected thereto by the selector 9 
when the audio data is read in at a high speed. 
On the other hand, the CD-ROM data storage 7 is connected to the audio 
buffer controller 10 and to the CD-ROM data processing section 6 by way of 
a selector 11. In the present invention, this CD-ROM data storage 7 can be 
used, apart from its original function as the storage for CD-ROM data, 
also as an input buffer memory of the audio signal processing section 1 by 
selectively connecting it to the audio buffer controller 10 through the 
selector 11 when the audio data is read in at a high speed. 
Reference numeral 12 denotes a track jump control circuit for jumping back 
the optical pick up device for a predetermined number of tracks of the 
disk when the EFM demodulated data writing operation is stopped when the 
audio data is read in at a high speed, and numeral 13 denotes a system 
controller for controlling the operation of the device as a whole. 
Referring to FIG. 1, the operation of the device in case audio data such as 
music, vocal sound and so on is read in at a high-speed is now explained 
as below. It should be noted that the disk here is rotated four times 
faster than the normal speed by a spindle motor and a speed servo circuit 
(not shown). Further, the selectors 9 and 11 respectively select the B 
terminal sides in accordance with a command from the system controller 13, 
so that the CD-ROM data storage 7 can be connected to the input terminal 
of the audio signal processing section 1 to be used as an input buffer 
memory thereof. 
In the above situation, when the demodulated data read in at the above 
four-time faster speed is input, it is sent to the CD-ROM data storage 7 
by way of the audio buffer controller 10 and the selector 11 so as to be 
stored therein one after the other. At this stage, while the data is being 
written into the CD-ROM data storage 7, the thus written data is 
simultaneously read out sequentially at the frequency equal to the 
sampling frequency of the audio signal, and thereafter each of these data 
is transmitted to the audio signal processing section 1 by way of the 
selector 11, audio data buffer controller 10, and the selector 9. 
The demodulated data thus transmitted to the audio signal processing 
section 1 is, after once stored in the audio signal data memory (RAM) 2 as 
conventionally done, checked by the CIRC checking method. Thereafter, the 
error-checked data is sent to the audio interface 3 and further to the D/A 
converter, and after the digital to analog conversion of the data in the 
D/A converter is completed, it is further fed to the low pass filter 5 
where the high-frequency component is taken away, so that the processed 
data is finally output as a reproduced audio signal formed in analog 
signal. 
In the above process, the writing operation to the CD-ROM data storage 7 is 
performed at the quadrupled speed, and the data reading operation 
therefrom is performed at the frequency equal to the sampling frequency of 
the audio signal. Thus, if the both operations are performed at this pace, 
there comes a moment at which the data writing operation exceeds the data 
reading operation. 
In order to cope with this phenomenon, the audio buffer controller 10 stops 
the writing operation of the EFM demodulated data to the CD-ROM data 
storage 7 just before the data writing operation exceeds the reading 
operation, although the data reading operation therefrom still continues, 
and simultaneously the controller 10 informs the system controller 13 of 
the fact that the CD-ROM data storage 7 is overflown. 
The system controller 13 sends a jump back signal to the track jump control 
circuit 12 on receiving this information, and moves the optical pick up 
device (not shown) for a predetermined pitch corresponding to a certain 
number of tracks. The number of tracks to be jumped back here is, for 
example, more than one, but not less than the number corresponding to the 
time required for reading out all the addresses in the CD-ROM data storage 
7 at the frequency equal to the sampling frequency. If a 128 k-byte RAM is 
used as described in the figure, the optical pick up device will have to 
be jumped back for one track only. 
When the data reading operation advances and takes all the written 
addresses to catch up with the point where the writing operation had been 
stopped, the audio buffer controller 10 detects it and resumes the writing 
operation starting from the data block following the data which had 
already been written. By this operation, it is made possible to read in 
the audio data from the disk at the quadrupled speed and simultaneously 
reproduce the thus read data at the normal speed. 
Referring to FIG. 1, the operation of the device in case audio data is read 
out at the normal reading speed is now explained as below. It should be 
noted that the disk here is rotated at the normal speed. Further, the 
selectors 9 and 11 respectively select the A terminal sides, whereby the 
CD-ROM data storage 7 is disconnected from the audio signal processing 
section 1. 
With the above situation, when the EFM demodulated data read out at the 
above speed is input, it is directly sent to the audio signal processing 
section 1 through terminal A of the selector 9, and after the conventional 
audio reproduction is through, the input data is further sent to the low 
pass filter 5 to be output as an audio reproduced signal. 
Next, also referring to FIG. 1, the operation of the device in case digital 
data is read out from a disk at a high speed or normal speed is now 
explained as follows. It should be noted that the selectors 9 and 11 are 
both set to the A terminal side, and by this operation, the CD-ROM data 
storage 7 is connected to the CD-ROM data processing section 6 so as to 
work as its CD-ROM data storage, which is the original function thereof. 
In this situation above, when the EFM demodulated data is input, the input 
data is first sent to the audio signal processing section 1 through 
terminal A of the selector 9, and after once stored in the audio signal 
memory 2 as conventionally done, an audio signal error correction is 
performed using the CIRC method at the audio signal processing section 1. 
Then, after being checked and corrected by the CIRC method, the data is 
sent to the CD-ROM data processing section 6, and thereafter it is further 
sent to the CD-ROM data storage 7 through terminal A of the reflector 11 
to be stored therein. The stored data is then checked with a view to 
correcting error in CD-rom data if any by using error checking codes P and 
Q at the CD-ROM data processing section 6, and then after being sent to 
the host computer interface 8, the corrected data is further sent to the 
host computer. 
FIGS. 2 and 3 respectively show concrete block circuits of this embodiment, 
wherein FIG. 2 is a concrete circuitry including an audio buffer 
controller 10 and CD-ROM data storage 7 of FIG. 1, whereas FIG. 3 is a 
diagram representing a concrete circuitry including an audio signal 
processing section 1 and CD-ROM data processing section 6 of FIG. 1. It is 
to be noted that like reference numerals in FIGS. 2 and 3 denote like or 
corresponding portions in FIG. 1. 
In the following, operations of these circuitries disclosed in these 
figures are explained individually with respect to each case. 
[1] In case of a reproduction of high-speed audio data 
Referring to FIG. 2, the EFM demodulated data DATA1 input, for example at 
the quadruple speed, is fed to the CD-ROM data storage 7 by way of the 
selector 11, and simultaneously it is fed to a sub-code synchronization 
detection & protection circuit 14 and also to a sub-code demodulation 
circuit 15. The EFM demodulated data input to the CD-ROM data storage 7 is 
stored in the address in accordance with the writing address information 
sent from a writing address generation circuit 105 at the timing of 
four-time faster by way of a selector 109, and simultaneously the thus 
stored data is read out from the address specified by the reading address 
generation circuit 106 at the timing of the normal speed also by way of 
the selector 109 so as to output a signal DATA3. 
On the other hand, the sub-code synchronization detection & protection 
circuit 14 detects a sub-code synchronization signal SBSY, and sends it to 
the sub-code demodulation circuit 15. The sub-code demodulation circuit 15 
demodulates the sub code in the EFM demodulated data using this sub-code 
synchronization signal SBSY, then sends is to a CRC check circuit 16, a 
system controller 13, and to a defected code protection circuit 101. 
The CRC check circuit 16 checks an error in each demodulated sub code, and 
in case there is an error such as defection of codes therein, the 
error-checked sub code is restored by the defected code protection circuit 
101, and stored into sub-code registers 102 and 103. The sub-code register 
102 is a register for storing the sub codes of the EFM demodulated data 
being currently received from the disk, and the sub-code register 103 is 
the one for storing the sub code of the data just before the CD-ROM data 
storage 7 is overflown and data writing operation to the storage 7 is 
prohibited. 
The address comparison circuit 107 compares the writing address output from 
the writing address generation circuit 105 and the reading address output 
from the reading address generation circuit 106 in order to detect whether 
or not they coincide with each other. When these reading and writing 
addresses coincide, it is indicated that the capacity of the CD-ROM data 
storage 7 is full up, and that if more EFM data is written, the new EFM 
data is written on the previously written EFM demodulated data which has 
not been read out yet, so that the previously written data is destroyed. 
Therefore, when the writing address and reading address coincide with each 
other, the address comparison circuit 107 generates an address coincidence 
signal ADCMP, and sends it to the sub-code register 103 and the system 
controller 13. When the sub-code register 103 receives this ADCMP signal, 
it stores the sub code of the data block just before the CD-ROM data 
storage 7 is overflown and the data writing operation thereto is 
prohibited. 
When the system controller 13 receives the above ADCMP signal, it stops the 
address incremental operation of the writing address generation circuit 
105 and simultaneously stops the writing operation into the CD-ROM data 
storage 7. Thus, thereafter, only a reading operation of the EFM 
demodulated data is permitted, and accordingly, the number of addresses 
available for writing EFM demodulated data is incremented in the CD-ROM 
data storage 7 afterwards. 
Furthermore, the system controller 13 sends a jump back signal to the track 
jump-back control circuit 12 to jump back the optical pick up device for 
one track, and then repeats the reading operation at the four time faster 
speed therefrom. It is to be noted that the data read in by this operation 
are not stored in the CD-ROM data storage 7, but the sub-codes thereof 
only are stored sequentially into the sub-code register 102. 
The sub-code comparison circuit 104 compares the EFM demodulated data 
currently being read out sequentially stored in the sub-code register 102 
with the sub code of the data block stored just before the stoppage of the 
writing operation stored in the sub-code register 103 so as to check 
whether or not these data coincide with each other. When the current sub 
code stored in the sub-code register 102 and the sub code stored in the 
sub-code register 103 coincide with each other, it is indicated that the 
data reading position of the optical pick up device has reached to the 
position where the data writing operation had previously been stopped. 
When the sub-code comparison circuit 104 detects that these sub-codes are 
the same, it sends a sub-code coincidence signal SBQCMP to the system 
controller 13 and to the writing address generation circuit 105 
simultaneously. 
When the system controller 13 receives the above SBQCMP signal, it sets a 
write enable condition again to the CD-ROM data storage 7. Further, the 
writing address generation circuit 105 resumes the address incremental 
operation which had been stopped previously. As a result, the EFM 
demodulated data is started to be written into the CD-ROM data storage 7 
at the quadrupled speed from the address just after the address where the 
writing operation had been stopped previously. 
Thereafter, when the writing operation of the EFM demodulated data catches 
up with the reading operation, and the writing address coincide with the 
reading address, then the writing operation is again stopped, so that the 
same process is repeated. This way, it is enabled that while EFM 
demodulated audio data are sequentially written into the CD-ROM data 
storage 7 one after the other at the four-time faster speed, they are 
simultaneously sent to the audio signal processing section 1 at the normal 
speed. 
By the way, in the above process, when the sub-code coincidence signal 
SBQCMP is not output from the sub-code comparison circuit 104 within a 
predetermined time, the system controller 13 calculates and obtains a sub 
code which is in the block more than one track before the sub code of the 
moment when the address coincidence signal ADCMP was output, and backs up 
the track jump control circuit 12, so that the audio data which has not 
been read out is started to be read out from the thus obtained sub code. 
The EFM demodulated data stored into the CD-ROM data storage 7 at the 
four-time faster speed and simultaneously read out therefrom at the normal 
speed is sent to the audio signal processing section 1 by way of the 
selector 9 shown in FIG. 3, and then stored in the audio signal memory 2. 
Thereafter when the CIRC error check is completed, the data is sent to the 
D/A converter 4 by way of an audio interface 3, and after the 
high-frequency component is signal is taken away from the low pass filter 
5, a reproduced audio signal is finally output in the form of analog 
signal. 
[2] In case of a conventional reproduction of audio data 
The EFM demodulated data DATA1 is sent to the audio signal processing 
section 1 by way of the selector 9, and then stored in the audio signal 
memory 2. Thereafter when the CIRC error check is completed, the data is 
sent to the D/A converter 4 by way of the audio interface 3 and then after 
the high-frequency component is taken away at the low pass filter 5, an 
analog-formed audio signal is finally output. 
It is to be noted that in the case above, the reading speed of the audio 
signal coincides with the rotational speed of the spindle motor that 
rotates the disk. Thereafter, when the spindle motor is rotated at the 
normal speed, the sound of the original speed is reproduced, and when it 
is rotated at four-time faster speed, the sound of quadrupled speed is 
reproduced. 
[3] In case of a reproduction of high-speed or normal speed audio data 
Regardless of normal or quadrupled speed, a reading of digital data from 
the disk is performed such that the EFM demodulated data DATA1 is sent to 
the audio signal processing section 1 by way of the selector 9 shown in 
FIG. 3, and then stored in the audio signal memory 2, and thereafter, it 
is checked by the CIRC method as disclosed above. When the CIRC check is 
completed, the signal DATA4 is transmitted to the CD-ROM data storage 7 by 
way of the selector 11 shown in FIG. 2. In short, when the digital data is 
read in and processed to be reproduced, the CD-ROM data storage 7 is used 
as a CD-ROM data buffer, which is the original use thereof. 
The data stored in the CD-ROM data storage 7 is sent to the CD-ROM data 
processing section 6 as shown in FIG. 3, wherein a detection of CD-ROM 
synchronization, descrambling, data correction of the CD-ROM, EDC check, 
detection of header are performed respectively at the CD-ROM 
synchronization detection & protection circuit 601, descrambler 602, 
CD-ROM data correction circuit 603, EDC check circuit 604, and at the 
header detection circuit 605. 
Then, the digital data signal DATA5 which is fed after the CD-ROM data 
correction is completed, is transmitted to a host-computer through the 
host computer interface 8 such as SCSI. At this stage, when the digital 
data is being read in at the normal speed, each data is sent at the normal 
speed (150K-bytes/s), and when read in at the quadrupled speed, each data 
is sent at the quadrupled speed (600K-bytes/s). It should be noted that 
during the above reading operation of the digital data, the system 
controller 13 sends a mute signal MUTE=0 to the audio interface 3 so as to 
set the output at the audio data reproducing side to o. 
As described above, the data processing regarding the audio data and that 
regarding digital data are explained individually. However, whether the 
data being read in is audio data or digital data can be easily identified 
by the sub code in the EFM demodulated data. Therefore, even when the 
audio and digital data are mixedly recorded in one disk, the audio data 
and digital data are selectively processed at a high speed from the disk 
by turns by switching either to the audio reproduction mode or to the 
digital reproduction mode in real time. 
As is obvious from the explanation above, by the present invention, even in 
the case of reading in digital data and audio data from one disk by turns, 
it is not necessary to slow down the rotational speed of the disk to 
reproduce the audio data. 
While the invention has been described with reference to specific 
embodiments, the description is illustrative and is not to be construed as 
limiting the scope of the invention.