Optical disk system

An analog-to-digital converter executes analog-to-digital conversion of a first analog video signal at a predetermined sampling frequency "fs". A time base converter converts a time base of an output signal from the analog-to-digital converter at a predetermined time base conversion frequency "ftci". A digital output signal from the time base converter is converted into a corresponding second analog video signal in response to a clock signal of a frequency corresponding to the frequency "ftci". The second analog video signal is converted into an FM video signal recorded on a video region of an optical disk. A binary audio digital signal is converted into a multi-level form digital audio signal. The binary audio digital signal has a data rate corresponding to the frequency "ftci". The multi-level form digital audio signal has a data rate "ftci/n" and 2.sup.n discrete amplitude levels where "n" denotes a predetermined integer. The multi-level form digital audio signal is converted into a corresponding analog audio signal in response to the clock signal of the frequency corresponding to the frequency "ftci". The analog audio signal is converted into an FM audio signal recorded on an audio region of the optical disk. A data signal generator generates a digital data signal at a data rate "ftci/m" where "m" denotes a predetermined integer. The digital data signal is converted into a corresponding analog data signal in response to the clock signal of the frequency corresponding to the frequency "ftci". The analog data signal is converted into an FM data signal recorded on a data region of the optical disk.

BACKGROUND OF THE INVENTION 
This invention relates to an optical disk, a system for recording 
information on an optical disk, and a system for reproducing information 
from an optical disk. 
An optical disk is a recording medium which can store a large amount of 
information. There are various optical disks, systems for recording 
information on an optical disk, and systems for reproducing information 
from an optical disk. 
IEEE Transactions on Consumer Electronics, Vol. 35, No. 3, August 1989, 
disclose an optical disk system for a wideband high definition video 
signal which is one of typical optical systems. 
As will be explained later, a prior art system for recording information on 
an optical disk, and a prior art system for reproducing information from 
an optical disk have some problems. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved optical disk 
system. 
A first aspect of this invention provides the following optical disk. In an 
information recording system comprising an analog-to-digital converter for 
executing analog-to-digital conversion of a first analog video signal at a 
predetermined sampling frequency "fs"; a time base converter for 
converting a time base of an output signal from the analog-to-digital 
converter at a predetermined time base conversion frequency "ftci"; 
digital-to-analog converting means for converting a digital output signal 
from the time base converter into a corresponding second analog video 
signal in response to a clock signal of a frequency corresponding to the 
time base conversion frequency "ftci"; FM modulating means for converting 
the second analog video signal into an FM video signal; a digital signal 
converter for converting a binary audio digital signal into a multi-level 
form digital audio signal, wherein the binary audio digital signal has a 
data rate corresponding to the time base conversion frequency "ftci", and 
the multi-level form digital audio signal has a data rate "ftci/n" and 
2.sup.n discrete amplitude levels where "n" denotes a predetermined 
integer; digital-to-analog converting means for converting the multilevel 
form digital audio signal into a corresponding analog audio signal in 
response to the clock signal of the frequency corresponding to the time 
base conversion frequency "ftci"; FM modulating means for converting the 
analog audio signal into an FM audio signal; a data signal generator for 
generating a digital data signal at a data rate "ftci/m" where "m" denotes 
a predetermined integer, wherein the generated digital data signal 
contains information representing positions of a video signal and an audio 
signal on programs; digital-to-analog converting means for converting the 
digital data signal into a corresponding analog data signal in response to 
the clock signal of the frequency corresponding to the time base 
conversion frequency "ftci"; FM modulating means for converting the analog 
data signal into an FM data signal: an optical disk comprises a video 
signal region for storing information of the FM video signal, an audio 
signal region for storing information of the FM audio signal, and a data 
signal region for storing the FM data signal. 
A second aspect of this invention provides an optical-disk information 
recording system comprising an analog-to-digital converter for executing 
analog-to-digital conversion of an analog video signal at a predetermined 
sapling frequency "fs"; a time base converter for converting a time base 
of an output signal from the analog-to-digital converter at a 
predetermined time base conversion frequency "ftci"; a digital signal 
converter for converting a binary audio digital signal into a multi-level 
form digital audio signal, wherein the binary audio digital signal has a 
data rate corresponding to the time base conversion frequency "ftci", and 
the multi-level form digital audio signal has a data rate "ftci/n" and 
2.sup.n discrete amplitude levels where "n" denotes a predetermined 
integer; a data signal generator for generating a digital data signal at a 
data rate "ftci/m" where "m" denotes a predetermined integer, wherein the 
generated digital data signal contains information representing positions 
of a video signal and an audio signal on programs; a multiplexer for 
multiplexing an output signal from the time base converter, the 
multi-level form digital audio signal, and the digital data signal; a 
digital-to-analog converter for converting an output signal from the 
multiplexer in response to a clock signal of a frequency corresponding to 
the time base conversion frequency "ftci"; a low pass filter for 
processing an output signal from the digital-to-analog converter; an FM 
modulator for executing FM modulation in response to an output signal from 
the low pass filter; and means for recording information of an output 
signal from the FM modulator on an optical disk. 
A third aspect of this invention provides an optical-disk information 
reproducing system comprising an FM demodulator for demodulating an FM 
signal reproduced from an optical disk; a low pass filter for processing 
an output signal from the FM demodulator; means for generating a clock 
signal of a predetermined time base conversion frequency "ftci" from a 
phase comparison reference signal contained in an output signal from the 
low pass filter; an analog-to-digital converter for executing 
analog-to-digital conversion of the output signal from the low pass filter 
in response to the clock signal of the time base conversion frequency 
"ftci"; a demultiplexer for demultiplexing an output signal from the 
analog-to-digital converter into a reproduced digital video signal, a 
reproduced digital audio signal, and a reproduced digital data signal, 
wherein the reproduced digital audio signal agrees with a multi-level form 
digital audio signal which has a data rate "ftci/n" and which has 2.sup.n 
discrete amplitude levels where "n" denotes a predetermined integer; a 
time base converter for converting a time base of the reproduced digital 
video signal into a predetermined time base corresponding to a 
predetermined sampling frequency "fs"; a digital-to-analog converter for 
executing digital-to-analog conversion of an output signal from the time 
base converter at the predetermined sampling frequency "fs", and for 
reproducing an analog video signal on the basis of the output signal from 
the time base converter; a digital signal converter for converting the 
reproduced digital audio signal into a binary digital audio signal having 
a-data rate corresponding to the time base conversion frequency "ftci"; 
and a data signal demodulator for recovering a data signal from the 
reproduced digital data signal, the recovered data signal having a data 
rate "ftci/m" where "m" denotes a predetermined integer. 
A fourth aspect of this invention provides an optical-disk information 
recording system comprising means for generating a first digital signal at 
a first predetermined data rate, the first digital signal representing 
video information; means for generating a second digital signal at a 
second predetermined data rate which is equal to the first predetermined 
data rate divided by a predetermined integer, the second digital signal 
representing audio information; means for multiplexing the digital video 
signal and the digital audio signal into a multiplexed digital signal; a 
digital-to-analog converter for converting the multiplexed digital signal 
into a multiplexed analog signal at a conversion clock frequency 
corresponding to the first predetermined data rate; and means for 
recording information represented by the multiplexed analog signal on an 
optical disk. 
A fifth aspect of this invention provides a system for processing an analog 
signal reproduced from an optical disk, the reproduced analog signal 
having video information components, audio information components, and 
burst signal components, the burst signal components representing a 
predetermined data rate, the system comprising means for detecting the 
predetermined data rate from the burst signal components; an 
analog-to-digital converter for converting the reproduced analog signal 
into a reproduced digital signal at a conversion clock frequency 
corresponding to the detected predetermined data rate; means for 
demultiplexing the reproduced digital signal into a reproduced digital 
video signal and a reproduced digital audio signal; means for processing 
the reproduced digital video signal at a frequency corresponding to the 
detected predetermined data rate; and means for processing the reproduced 
digital audio signal at a frequency which is equal to the detected 
predetermined data rate divided by a predetermined integer.

DESCRIPTION OF THE PRIOR ART 
With reference to FIG. 1, a prior art system for recording information on 
an optical disk 1 includes analog-to-digital (A/D) converters 3a and 3b 
receiving component analog video signals, that is, an analog luminance 
signal Y and an analog color signal C respectively. The analog luminance 
signal Y and the analog color signal C are converted by the A/D converters 
3a and 3b into corresponding digital signals respectively. The A/D 
conversion of the analog luminance signal Y and the analog color signal C 
uses a sampling clock signal having a predetermined frequency "fs". 
To enable the luminance signal and the color signal to be recorded on a 
common time base, the digital luminance signal and the digital color 
signal outputted from the A/D converters 3a and 3b are subjected to a time 
base compression process or a time base adjustment process, and are 
multiplexed or combined into a composite video signal by a time base 
compression circuit 4. 
To enable segments of the video signal to be recorded on respective optical 
disk regions each having a predetermined time width, the composite video 
signal outputted from the time base compression circuit 4 is subjected to 
a time base conversion process by a time base conversion circuit 5. The 
time base conversion process uses the clock signal of the frequency "fs" 
and a second clock signal of a predetermined frequency "ftci". The digital 
video signal outputted from the time base conversion circuit 5 has a clock 
period corresponding to the time base conversion frequency "ftci". 
The digital video signal outputted from the time base conversion circuit 5 
is converted by a digital-to-analog (D/A) converter 6 into a corresponding 
analog signal. The D/A conversion of the digital video signal uses the 
clock signal of the frequency "ftci". 
The analog video signal outputted from the D/A converter 6 is transmitted 
to an FM modulation circuit (a frequency-modulation circuit) 8 via a low 
pass filter 7 and a switch (no reference numeral). As will be made clear 
later, the analog video signal is multiplexed with an analog audio signal 
by the switch before entering the FM modulation circuit 8. The FM 
modulation circuit 8 modulates the frequency of a carrier in accordance 
with the received analog video signal, and converts the analog video 
signal into an FM video signal. 
A laser drive circuit 9 drives a laser light source (not shown) in response 
to the output FM video signal from the FM modulation circuit 8 so that a 
laser light beam emitted from the laser light source will be modulated in 
accordance with the FM video signal. The laser light beam is applied to 
the optical disk 1 so that information represented by the FM video signal 
will be recorded on the optical disk 1. 
An analog audio signal (an analog audio-information signal) is converted by 
an A/D converter 10 into a corresponding digital signal. The digital audio 
signal outputted from the A/D converter 10 is processed by an audio signal 
processor 11. Specifically, the audio signal processor 11 executes an 
error correction code adding process and an interleaving process on the 
digital audio signal. The audio signal processor 11 outputs a binary 
digital audio signal having a predetermined data rate "fa". 
To enable segments of the audio signal to be recorded on respective optical 
disk regions each having a predetermined time width, the digital audio 
signal outputted from the audio signal processor 11 is converted by a 
digital signal conversion circuit 12 into a multi-level form digital 
signal which has "2.sup.l " discrete amplitude levels and which has a 
predetermined data rate "fa/l", where the character "2.sup.l " denotes the 
total number of the discrete amplitude levels and the character "l" 
denotes a predetermined integer. This signal conversion uses a clock 
signal having a frequency "fa" and a clock signal having a frequency 
"fa/l". 
The multi-level form digital audio signal outputted from the digital signal 
conversion circuit 12 is transmitted to a D/A converter 13 via a switch 
2A. The multi-level form digital audio signal outputted from the digital 
signal conversion circuit 12 is converted by the D/A converter 13 into a 
corresponding analog signal. The D/A conversion of the multi-level form 
digital audio signal uses the clock signal of the frequency "fa/l". 
The analog audio signal outputted from the D/A converter 13 is transmitted 
to the FM modulation circuit 8 via a low pass filter 14, a phase 
adjustment circuit 15, and a switch 2B. The analog audio signal is 
multiplexed with the analog signal by the switch 2B before entering the FM 
modulation circuit 8. The FM modulation circuit 8 modulates the frequency 
of a carrier in accordance with the received analog audio signal, and 
converts the analog audio signal into an FM audio signal. 
The laser drive circuit 9 drives the laser light source (not shown) in 
response to the output FM audio signal from the FM modulation circuit 8 so 
that the laser light beam emitted from the laser light source will be 
modulated in accordance with the FM audio signal. The laser light beam is 
applied to the optical disk 1 so that information represented by the FM 
audio signal will be recorded on the optical disk 1. 
The low pass filter 7 for processing the video signal and the low pass 
filter 14 for processing the audio signal have different pass bands, so 
that the low pass filters 7 and 14 provide different group delay times. 
The phase adjustment circuit 15 serves to compensate for the difference 
between the group delay times provided by the low pass filters 7 and 14. 
A data signal generation circuit 16 outputs a digital data signal at a 
predetermined data rate "fa/l/k", where the character "k" denotes a 
predetermined integer. The output digital data signal from the data signal 
generating circuit 16 represents addresses and time codes denoting 
positions of the video signal and the audio signal on programs. The output 
digital data signal from the data signal generation circuit 16 is 
multiplexed with the output audio signal from the digital signal 
conversion circuit 12 by the switch 2A, and is then transmitted to the D/A 
converter 13. 
The prior art recording system of FIG. 1 has the following problems. Since 
the video time base conversion frequency "ftci" completely disagrees with 
the audio data rate "fa", it is necessary to provide the two D/A 
converters 6 and 13, and the two low pass filters 7 and 14. In addition, 
it is necessary to provide the phase adjustment circuit 15. In the event 
that the clock signal having the frequency "ftci" leaks to the system 
portion operated in response to the clock signal having the frequency "fa" 
and that the clock signal having the frequency "fa" leaks to the system 
portion operated in response to the clock signal having the frequency 
"ftci", there occurs crosstalk between the independent signals in the two 
system portions. 
With reference to FIG. 2, a prior art system for reproducing information 
from an optical disk 1 includes a preamplifier 50 and an FM demodulation 
circuit 17. An information signal reproduced from the optical disk 1 is 
transmitted to the FM demodulation circuit 17 via the preamplifier 50. The 
reproduced signal is subjected to an FM demodulation process by the FM 
demodulation circuit 17, being converted into a reproduced baseband analog 
signal. 
The reproduced analog signal outputted from the FM demodulation circuit 17 
is demultiplexed by a switch 51 into a reproduced analog video signal and 
a reproduced analog audio signal. The reproduced analog video signal is 
transmitted to a clock reproduction circuit 19 and an A/D converter 20 via 
a low pass filter 18. The reproduced analog audio signal is transmitted to 
a clock reproduction circuit 26 and an A/D converter 27 via a phase 
adjustment circuit 24 and a low pass filter 25. 
The low pass filter 18 for processing the video signal and the low pass 
filter 25 for processing the audio signal have different pass bands, so 
that the low pass filters 18 and 25 provide different group delay times. 
The phase adjustment circuit 24 serves to compensate for the difference 
between the group delay times provided by the low pass filters 18 and 25. 
The reproduced analog video signal is further processed as follows. The 
clock reproduction circuit 19 reproduces a clock signal from the 
reproduced analog video signal by using a PLL (phase-locked loop). The 
reproduced clock signal has the frequency "ftci". The reproduced analog 
video signal is converted by the A/D converter 20 into a corresponding 
digital signal. The A/D conversion of the reproduced analog video signal 
uses the clock signal having the frequency "ftci". 
The reproduced digital video signal outputted from the A/D converter 20 is 
subjected to a time base conversion process by a time base conversion 
circuit 21. The time base conversion process uses the clock signal of the 
frequency "ftci" and a second clock signal of the sapling frequency "fs". 
The reproduced digital video signal outputted from the time base 
conversion circuit 21 has a data rate corresponding to the sampling 
frequency "fs". 
The reproduced digital video signal outputted from the time base conversion 
circuit 21 is subjected to a time base expansion process or a time base 
adjustment process, and is demultiplexed into a reproduced digital 
luminance signal and a reproduced digital color signal by a time base 
expansion circuit 22. The reproduced digital luminance signal is converted 
by a D/A converter 23a into a corresponding reproduced analog luminance 
signal Y. The reproduced digital color signal is converted by a D/A 
converter 23b into a corresponding reproduced analog color signal C. The 
D/A conversion of the reproduced digital luminance signal and the 
reproduced digital color signal uses the sapling clock signal of the 
frequency "fs". 
The reproduced analog audio signal is further processed as follows. The 
clock reproduction circuit 26 reproduces a clock signal from the 
reproduced analog audio signal by using a PLL (phase-locked loop). The 
reproduced clock signal has the frequency "fa/l". The reproduced analog 
audio signal is converted by the A/D converter 27 into a corresponding 
digital signal. The A/D conversion of the reproduced analog audio signal 
uses the clock signal having the frequency "fa/l". 
The reproduced digital audio signal outputted from the A/D converter 27 is 
demultiplexed by a switch 52 into a reproduced digital pure audio signal 
and a reproduced digital data signal. The reproduced digital pure audio 
signal agrees with a multi-level form digital audio signal. The reproduced 
digital pure audio signal is transmitted to a digital signal conversion 
circuit 28. The reproduced digital data signal is transmitted to a data 
signal demodulation circuit 31. 
The reproduced digital pure audio signal, that is, the reproduced 
multi-level form digital audio signal, is converted by the digital signal 
conversion circuit 28 into a corresponding binary digital signal which has 
the data rate "fa". This signal conversion uses a clock signal having the 
frequency "fa" and the clock signal having the frequency "fa/l". 
The digital audio signal outputted from the digital signal conversion 
circuit 28 is processed by an audio signal processor 29. Specifically, the 
audio signal processor 29 executes an error correction process and a 
de-interleaving process on the digital audio signal. 
The reproduced digital audio signal outputted from the audio signal 
processor 29 is converted by a D/A converter 30 into a corresponding 
reproduced analog audio signal. 
The reproduced digital data signal is subjected to a demodulation process 
by the data signal demodulation circuit 31 so that data is recovered from 
the digital data signal. The demodulation process uses a clock signal of 
the frequency "fa/l". 
The prior art reproducing system of FIG. 2 has the following problems. 
Since the video time base conversion frequency "ftci" completely disagrees 
with the audio data rate "fa", it is necessary to provide the two A/D 
converters 20 and 27, and the two low pass filters 18 and 25. In addition, 
it is necessary to provide the phase adjustment circuit 24. In the event 
that the clock signal having the frequency "ftci" leaks to the system 
portion operated in response to the clock signal having the frequency "fa" 
and that the clock signal having the frequency "fa" leaks to the system 
portion operated in response to the clock signal having the frequency 
"ftci", there occurs crosstalk between the independent signals in the two 
system portions. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 3, a system for recording information on an optical 
disk 101 includes analog-to-digital (A/D) converters 103a and 103b 
receiving component analog video signals, that is, an analog luminance 
signal Y and an analog color signal C respectively. The analog luminance 
signal Y and the analog color signal C are converted by the A/D converters 
103a and 103b into corresponding digital signals respectively. The A/D 
conversion of the analog luminance signal Y and the analog color signal C 
uses a sampling clock signal having a predetermined frequency "fs". 
To enable the luminance signal and the color signal to be recorded on a 
common time base, the digital luminance signal and the digital color 
signal outputted from the A/D converters 103a and 103b are subjected to a 
time base compression process or a time base adjustment process, and are 
multiplexed or combined into a composite video signal by a time base 
compression circuit 104. 
To enable segments of the video signal to be recorded on respective optical 
disk regions each having a predetermined time width, the composite video 
signal outputted from the time base compression circuit 104 is subjected 
to a time base conversion process by a time base conversion circuit 105. 
The time base conversion process uses the clock signal of the frequency 
"fs" and a second clock signal of a predetermined frequency "ftci". The 
digital video signal outputted from the time base conversion circuit 105 
has a clock period corresponding to the time base conversion frequency 
"ftci". 
An analog audio signal (an analog audio-information signal) is converted by 
an A/D converter 110 into a corresponding digital signal. The digital 
audio signal outputted from the A/D converter 110 is processed by an audio 
signal processor 111. Specifically, the audio signal processor 111 
executes an error correction code adding process and an interleaving 
process on the digital audio signal. The audio signal processor 111 
outputs a binary digital audio signal having a predetermined data rate 
which agrees with or corresponds to the time base conversion frequency 
"ftci". 
To enable segments of the audio signal to be recorded on respective optical 
disk regions each having a predetermined time width, the digital audio 
signal outputted from the audio signal processor 111 is converted by a 
digital signal conversion circuit 112 into a multi-level form digital 
signal which has "2.sup.n " discrete amplitude levels and which has a 
predetermined data rate "ftci/n", where the character "2.sup.n " denotes 
the total number of the discrete amplitude levels and the character "n" 
denotes a predetermined integer. This signal conversion uses the clock 
signal having the frequency "ftci" and a clock signal having the frequency 
"ftci/n". 
A data signal generation circuit 116 outputs a digital data signal at a 
predetermined data rate "ftci/m", where the character "m" denotes a 
predetermined integer. The output digital data signal from the data signal 
generation circuit 116 represents addresses and time codes denoting 
positions of the video signal and the audio signal on programs. 
The output digital video signal from the time base conversion circuit 105, 
the output digital audio signal from the digital signal conversion circuit 
112, and the output digital data signal from the data signal generation 
circuit 116 are multiplexed by a multiplexer switch 143 in a time division 
fashion such that they will be recorded on video signal regions, audio 
signal regions, and data signal regions of the optical disk 101 
respectively. 
A burst signal generation circuit 160 includes a frequency divider which 
divides the frequency "ftci" of the clock signal by a predetermined 
integer to generate a burst signal of a predetermined frequency from the 
clock signal of the frequency "ftci". The burst signal is outputted from 
the burst signal generation circuit 160 to the multiplexer switch 143. A 
portion of the burst signal is added by the multiplexer switch 143 to a 
former part of each of 1-line segments of the multiplexed signal 
containing the video components, the audio components, and the data 
components. By the function of a low pass filter 107 which will be 
explained later, the burst components are shaped into a sinusoidal 
waveform. 
The output digital signal from the multiplexer switch 143 is converted by a 
digital-to-analog (D/A) converter 106 into a corresponding analog signal. 
The D/A conversion of the digital video signal uses the clock signal of 
the frequency "ftci". 
The output analog signal from the D/A converter 106 is transmitted to an FM 
modulation circuit (a frequency-modulation circuit) 108 via the low pass 
filter 107. The FM modulation circuit 108 modulates the frequency of a 
carrier in accordance with the received analog signal, and converts the 
analog signal into an FM signal. 
A laser drive circuit 109 drives a laser light source (not shown) in 
response to the output FM signal from the FM modulation circuit 108 so 
that a laser light beam emitted from the laser light source will be 
modulated in accordance with the FM signal. The laser light beam is 
applied to the optical disk 101 so that information represented by the FM 
signal will be recorded on the optical disk 101. 
The recording system of FIG. 3 has the following advantages. Only a single 
D/A converter 106 suffices. In addition, only a single low pass filter 107 
suffices. Since processing the video signal, processing the audio signal, 
and processing the data signal are executed basically at a common clock 
frequency corresponding to the time base conversion frequency "ftci", it 
is possible to prevent crosstalk which would be caused if different clock 
signals are used and they leak. 
With reference to FIG. 4, a system for reproducing information from an 
optical disk 101 includes a preamplifier 132 and an FM demodulation 
circuit 117. An information signal reproduced from the optical disk 101 is 
transmitted to the FM demodulation circuit 117 via the preamplifier 132. 
The reproduced signal is subjected to an FM demodulation process by the FM 
demodulation circuit 117, being converted into a reproduced baseband 
analog signal. 
The reproduced analog signal outputted from the FM demodulation circuit 117 
is transmitted to a clock reproduction circuit 119 and an A/D converter 
120 via a low pass filter 118. The clock reproduction circuit 119 
reproduces a clock signal from the reproduced analog signal by using a PLL 
(phase-locked loop). The reproduced clock signal has the frequency "ftci". 
Specifically, the clock reproduction circuit 119 extracts a 
fixed-frequency burst signal, that is, a phase comparison reference 
signal, from the reproduced analog signal. The clock reproduction circuit 
119 locks the phase of a base clock signal to the phase of the phase 
comparison reference signal, and the base clock signal locked to the phase 
comparison reference signal is used as the reproduced clock signal having 
the frequency "ftci". The reproduced clock signal having the frequency 
"ftci" is outputted from the clock reproduction circuit 119. 
The reproduced analog signal is converted by the A/D converter 120 into a 
corresponding digital signal. The A/D conversion of the reproduced analog 
signal uses the clock signal having the frequency "ftci". 
The reproduced digital video signal outputted from the A/D converter 20 is 
demultiplexed by a demultiplexer switch 144 into a signal reproduced from 
the video signal regions of the optical disk 101 (a reproduced digital 
video signal), a signal reproduced from the audio signal regions of the 
optical disk 101 (a reproduced digital audio signal), and a signal 
reproduced from the data signal regions of the optical disk 101 (a 
reproduced digital data signal). 
The reproduced digital video signal is transmitted from the demultiplexer 
switch 144 to a time base conversion circuit 121, and is subjected to a 
time base conversion process by the time base conversion circuit 121. The 
time base conversion process uses the clock signal of the frequency "ftci" 
and a second clock signal of the sampling frequency "fs". The reproduced 
digital video signal outputted from the time base conversion circuit 121 
has a data rate corresponding to the sapling frequency "fs". 
The reproduced digital video signal outputted from the time base conversion 
circuit 121 is subjected to a time base expansion process or a time base 
adjustment process, and is demultiplexed into a reproduced digital 
luminance signal and a reproduced digital color signal by a time base 
expansion circuit 122. The reproduced digital luminance signal is 
converted by a D/A converter 123a into a corresponding reproduced analog 
luminance signal Y. The reproduced digital color signal is converted by a 
D/A converter 123b into a corresponding reproduced analog color signal C. 
The D/A conversion of the reproduced digital luminance signal and the 
reproduced digital color signal uses the sampling clock signal of the 
frequency "fs". 
The reproduced digital audio signal separated by the demultiplexer switch 
144 agrees with a multi-level form digital audio signal having the data 
rate "ftci/n". The reproduced digital audio signal is transmitted from the 
demultiplexer switch 144 to a digital signal conversion circuit 128. The 
reproduced digital audio signal, that is, the reproduced multi-level form 
digital audio signal, is converted by the digital signal conversion 
circuit 128 into a corresponding binary digital audio signal which has the 
data rate "ftci". This signal conversion uses a clock signal having the 
frequency "ftci/n" and the clock signal having the frequency "ftci". 
The digital audio signal outputted from the digital signal conversion 
circuit 128 is processed by an audio signal processor 129. Specifically, 
the audio signal processor 129 executes an error correction process and a 
de-interleaving process on the digital audio signal. 
The reproduced digital audio signal outputted from the audio signal 
processor 129 is converted by a D/A converter 130 into a corresponding 
reproduced analog audio signal. 
The reproduced digital data signal is transmitted from the demultiplexer 
switch 144 to a data signal demodulation circuit 131, and is subjected to 
a demodulation process by the data signal demodulation circuit 131 so that 
data is recovered from the digital data signal. The demodulation process 
uses a clock signal of the frequency "ftci/m". 
The reproducing system of FIG. 4 has the following advantages. Only a 
single A/D converter 120 suffices. In addition, only a single low pass 
filter 118 suffices. Since processing the video signal, processing the 
audio signal, and processing the data signal are executed basically at a 
common clock frequency corresponding to the time base conversion frequency 
"ftci", it is possible to prevent crosstalk which would be caused if 
different clock signals are used and they leak. 
A description will now be given of the formats of various signals and the 
optical disk 101. The FM signal recorded on the optical disk 101 is 
separated into a sequence of fields. As shown in FIG. 5, a 1-field segment 
32 of the recorded FM signal has two similar sets 33 each having a 
sequence of a data signal 34, an audio signal 35, and a video signal 36. 
The data signal 34, the audio signal 35, and the video signal 36 are 
recorded on a data signal region, an audio signal region, and a video 
signal region of the optical disk 101 respectively. 
The video signal components of the signal inputted into the FM modulation 
circuit 108 are separated into a sequence of lines. As shown in FIG. 6, a 
1-line segment 37 of the video signal has a sequence of a phase comparison 
reference signal 38, a color signal 39 (a color signal C), and a luminance 
signal 40 (a luminance signal Y). The phase comparison reference signal 38 
agrees with a sinusoidal burst signal having a predetermined frequency 
which equals the time base conversion frequency "ftci" divided by a 
predetermined integer. As described previously, the clock signal having 
the frequency "ftci" is reproduced by locking the phase of a basic clock 
signal to the phase of the phase comparison reference signal 38. 
The audio signal components of the signal inputted into the FM modulation 
circuit 108 are separated into a sequence of lines. As shown in FIG. 7, a 
1-line segment 37 of the audio signal has a sequence of a phase comparison 
reference signal 38 and a multilevel form digital audio signal A. The 
multi-level form digital audio signal A has, for example, four discrete 
amplitude levels 41a, 41b, 41c, and 41d. In this case, the multi-level 
form digital audio signal A has a data rate "ftci/2" so that it can be 
demodulated in response to a clock signal of a frequency equal to the time 
base conversion frequency "ftci". 
The data signal components of the signal inputted into the FM modulation 
circuit 108 are separated into a sequence of lines. As shown in FIG. 8, a 
1-line segment 37 of the data signal has a sequence of a phase comparison 
reference signal 38 and a binary digital data signal D. The binary digital 
data signal D contains codes of addresses and time codes denoting 
positions of a video signal and an audio signal on programs. The binary 
digital data signal D has two discrete amplitude levels 42a and 42b. The 
binary digital data signal D has the data rate "ftci/m" so that it can be 
demodulated in response to a clock signal of a frequency equal to the time 
base conversion frequency "ftci".