JPH0156460B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recording and reproducing multiplexed information, and more particularly to a recording and reproducing method for multiplexed information in which not only video signals but also different types of multi-channel signals such as audio information are multiplexed, recorded, and reproduced. In the case of a video disc as a recording medium, in addition to video signals, other types of information signals such as audio information are also multiplexed and recorded. In this case, the video signal is frequency modulated, and the audio signal is a two-channel signal for stereo or bilingual program mode, and each channel signal is transmitted through two independent audio carriers, which are also frequency modulated. By modulating it, it is recorded on a video disc together with the previous frequency-modulated video information. In addition to such two-channel audio information, there is a demand for multiplexing two-channel information, for example, but in the case of video discs that must be multiplexed with video information with a wide dedicated bandwidth, this is not possible for reasons that will be detailed later. However, the reality is that there is almost no bandwidth available for recording two additional channels, and when multiplexing four channels of audio, there is also the constraint that compatibility with existing systems must be considered. be. SUMMARY OF THE INVENTION An object of the present invention is to provide a multiple information storage/reproduction method that does not have any adverse effect on video information and can maintain compatibility with existing systems. Another object of the present invention is to provide a multiple information recording/reproducing system with good reproduction characteristics. The multiplexed information recording and reproducing method according to the present invention modulates two subcarriers of the same frequency with two subchannel signals, respectively, superimposes each of these modulated signals and two main channel signals, and then superimposes these two sets. Frequency modulation of two main carriers of different frequencies by signals, recording on a recording medium using these modulated signals, frequency separation and extraction of the main carriers from each other during reproduction,
The present invention is characterized in that detection is performed using different frequency detection means, and one of these two sets of detection outputs is alternatively selected and supplied to a common subchannel demodulation means. DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to better understand the features and effects of the present invention, a detailed explanation will be given below using the drawings. FIG. 1 is a diagram showing an example of the frequency spectrum of a video disk, which is a recording medium, in the case where existing two-channel audio multiplexed information is included. That is, the color video signal is 8.1M
The Hz carrier is FM (frequency modulated), and the sync chip level is 7.6MHz and the white peak level is
The band has been converted to 9.3MHz, which is indicated by A in the figure. B is chroma signal (3.58MHz)
C is the first sideband wave, and C is also the second sideband wave. Also, the video signal is a direct current (DC)
Since it is a wideband information signal from the component to 5.6MHz, ±
It also has a modulation band D of 5.6MHz (3.15-14.35MHz). Furthermore, the noise spectrum peculiar to video discs is as shown by curve E in the figure. Taking this fact into consideration, for existing video discs, approximately 2.3MHz indicated by F and approximately 2.3MHz indicated by G are used.
Select two 2.8MHz audio carriers,
Each of these audio carriers is approximately 40Hz to 20KHz.
FM by two-channel audio signal with a band of
Processing and audio multiplexing are attempted. In addition to the 2 channel audio information, for example, 2
When it is desired to multiplex channel information, it is difficult to set up a new audio carrier, as is clear from the frequency spectrum of FIG. Even if 4-channel audio multiplexing were possible, as mentioned above, there would be the issue of compatibility with existing playback devices, and it would also be necessary to consider the characteristics when playing back on existing playback devices. It is also undesirable to cause it to deteriorate. This device is designed to multiplex audio information in four channels in consideration of this point. FIG. 2 is a block diagram of a recording system for four-channel audio multiplexing, in which audio inputs for the first to fourth channels are provided, for example, the first and second channels.
The first language for the channel (Japanese as an example)
A stereo signal is input to the matrix circuit 1. As audio inputs of the third and fourth channels, for example, stereo signals in a second language (English as an example) are input to the matrix circuit 2. Of course, it is also possible to input audio signals in four independent languages as four-channel information. Also, the first channel and the third channel
Existing two-channel audio information can also be transmitted by inputting left and right stereo signals or two-language signals to only the channels, respectively. In this way, there are two sets of stereo signal modes (designated MPX stereo mode), one independent
A matrix control signal is sent from a control circuit (not shown) that identifies the two-language signal mode (referred to as MPX monaural mode) and the existing signal mode using only the first and third channels (referred to as NO-MPX mode). and matrix circuit 1
and 2. Each matrix circuit performs operations such as deriving the addition/subtraction calculation outputs of the two input signals, respectively, or deriving the two inputs as they are, depending on the control signal. In the case of MPX stereo mode, the main channel signal (L+R), which is the addition output of the input signals, is output to each output line 3 and 4 of matrix circuits 1 and 2, and becomes one input each of mixers 7 and 8. . On the other hand, each output line 5 and 6 of the matrix circuits 1 and 2 outputs a subchannel signal (LR) which is a subtracted output of the input signal. Both subchannel signals are input to modulators 9 and 10, respectively, to modulate a predetermined subcarrier signal, and are preferably subjected to FM processing. The subchannel information thus modulated becomes input to mixers 7 and 8, and is combined with the previous main channel signals 3 and 4, respectively, and input to modulators 11 and 12. The main carriers of the FM modulators 11 and 12 are selected to be 2.3 MHz and 2.8 MHz, which are the same as the audio carrier frequencies of existing video discs, in order to maintain compatibility with existing reproduction systems. These FM modulated outputs are sent to the mixer 1 along with the FM processed video information in the modulator 13.
The signals are mixed at step 4 and passed through limiter 15 to form a video disc recording signal. On the other hand, a subcarrier level controller 16 is provided, and the subcarrier level is controlled by a control signal indicating a program mode of recorded information, and the program mode of multiplexed information is identified by this subcarrier level. It's becoming like that. FIG. 3 is a diagram showing the frequency spectrum of the input signals to the FM modulators 11 and 12 of FIG. 2. The main channel signal (L+R) has a band of approximately 40Hz to 20KHz. Subchannel signal (L-
R) is the subcarrier in modulators 9 and 10.
It is FM modulated and has a maximum deviation of ±15KHz. The frequency of this subcarrier is selected to be _3H ( _H is the horizontal synchronization signal frequency in the video signal), and in the case of the NTSC system, _H
= 15.734KHz, so 3 _H = 47.25KHz,
For B, G, I-PAL system, _H = 15.625KHz
Therefore, 3 _H = 46.88KHz. In the FM modulators 11 and 12, the main channel signal is modulated so that the frequency deviation of the main carrier is ±100 KHz. In addition, when modulating subchannels, ±45KHz for MPX monaural and ±45KHz for MPX stereo.
The carrier frequency deviation is made to be 60KHz. For this purpose, as shown in FIG. 2, a subcarrier level controller 16 is provided to control the subcarrier level according to the recording program mode.
% level (main channel carrier is ±100K
Hz (100% modulation level), the subcarrier level is controlled to be 45% in MPX monaural mode and 60% in MPX stereo mode. Since there is no subchannel signal in the NO-MPX mode, the subcarrier level is controlled to be zero. Now, when we think about TV audio multiplex broadcasting,
In this broadcast, as in the system shown in Figure 2, the sub-carrier is subjected to FM processing using the sub-channel signal, and this FM output and the main channel are used to perform FM on the main carrier, but the receiving side uses the main carrier method. Since it is common, it is necessary to select a subcarrier frequency _SC which is basically inconspicuous for buzz beats, and therefore it is selected to be n _H (n is an integer). In addition, since buzz tends to increase as the frequency increases, the subcarrier frequency in this broadcast is set to _2H . However, with the video disc playback system,
Since a so-called split carrier system is used instead of an intercarrier system, there is no buzzbeat generation in principle. Therefore, the subcarrier frequency of the subcarrier is not limited to n _H from the point of view of buzzbeat. However, the subcarrier frequency _SC is limited to n _H for completely different reasons as described below. In a video disc system, as shown in Figure 2, an audio carrier and a video carrier are combined and added to a limiter, and the limiter output is recorded by providing pits on the disc. If the signal is distorted, beats from the audio carrier will appear on the playback screen. This beat is composed of the audio main carrier frequency _AC and the horizontal sync signal frequency _H.
The _{way it} appears is determined by _the relationship _with The fact is that the beats are the least noticeable. Therefore, the audio main carrier frequencies are selected to be 146.25 _H = 2.301136 MHz and 178.75 _H = 2.812499 MHz, as shown by F and G in FIG.
If subchannel audio multiplexing as explained in FIGS. 2 and 3 is performed on this audio main carrier _AC , a spectrum of upper and lower sidebands _U and _D as shown in FIG. 4A will be generated in the case of no modulation. Beats on the screen are also generated by both sideband waves from this subchannel as well as from the main channel. Therefore, the frequency _U of both sidebands,
It would also be desirable for _D to have a 1/4 offset from _nH . Therefore, it is necessary that | _U −n _H |=1/4 ...(2) | _D −n _H |=1/4 ...(3). On the other hand, since there is the relationship _U = _AC + _SC ...(4) _D = _AC − _SC ...(5), from equations (1), (2) and (4), we also have (1), (3) From equation (5), _SC needs to be n _H. Next, when using the audio multiplexing system shown in Figures 2 and 3, the main channel has a frequency deviation of ±100KHz when the modulation depth is 100%, and the frequency deviation is ±100KHz when the modulation depth of the subchannel is 100%.
15KHz deviation, modulation audio frequency band
10KHz, 60% of main channel level 100%
(In MPX stereo mode) In other words, ±60KHz is the frequency shift due to the subchannel, and the necessary bandwidth with the subcarrier frequency as _nH is very complicated to calculate in detail, but as a rough guide, it can be found by the following formula. 100+n _H +15+10+60 ≦250 (KHz) Here, 250KHz on the right side of the above inequality indicates half of 500KHz, which is the difference between the two audio main carriers 2.3MHz and 2.8MHz, and the maximum of one audio main carrier. Indicates the possible deviation width. Therefore, the relationship n≦4 is obtained. Furthermore, when changing the subchannel carrier frequency _SC in a video disc, there is a fact that the noise characteristics become extremely small near _3H as shown in Figure 4B, and from the relationship between this and n≦4, _SC = _3H . By doing this, it is possible to minimize the influence of audio beats on the playback screen and to prevent the influence of audio information on each other due to audio multiplexing, and also to improve the S/N ratio. Additionally, video disc playback devices are equipped with a tangential servo system for time axis correction, which detects the phase error of the reproduced color burst signal. During a certain vertical blanking period, no accurate error signal is generated, and therefore the information detection points are randomly swung at high frequency in the tangential direction. In this case, the main carrier is modulated accordingly, but since the subcarrier that is directly modulated by the subchannel signal has a low frequency of _3H , it generates less noise in the reproduced signal compared to modulation using a high frequency as a carrier. There are some advantages. Having described the above recording system, the reproducing system will now be described using FIG. Vickup 17
The reproduced RF (high frequency) signal is separated from only audio multiplexed information by an LPF (low pass filter) 18. Note that the video information reproduction system is not illustrated. The output of the LPF 18 is supplied to BPFs (band pass filters) 19 and 20. For example, BPF19
The BPF
20 has a center frequency of 2.8 MHz and allows the signal to pass through the vicinity thereof. The respective outputs of the BPFs 19 and 20 are applied to FM detectors 21 and 22 and subjected to FM detection, respectively. Each output of FM detector 21 and 22 is connected to switch 2.
3 is alternatively selected and applied to the next stage LPF 24 and BPF 25. Further, the output of the detector 22 is supplied to the LPF 26, and the LPFs 24 and 26 have a characteristic of allowing only audio band signals of 20 KHz or less to pass through. The BPF 25 has a pass characteristic of ±22.5 KHz centered around the subcarrier frequency _3H , and its output is subjected to FM detection in the detector 27. This detection output and LPF24,2
6 outputs are introduced into a switching circuit 28, and according to a control signal from a switch controller 29, these three inputs are switched and outputted to two signal lines 30 and 31 as desired. Hold capacitors 32 and 33 are provided between both signal lines 30 and 31 and the reference potential point and are used for dropout compensation operation. The signals on lines 30 and 31 are routed to amplifier 34.
and 35 to the matrix circuit 36, and in response to a control signal from the matrix controller 37, the two inputs are derived as desired two-channel signal outputs. The rectifier 38, LPF
39 and a level discriminator 40 are provided to discriminate the recording program mode (MPX stereo, MPX monaural, NO-) according to the subcarrier level.
MPX mode) is performed, and a corresponding signal is output. This mode discrimination signal becomes each control signal for the switch controller 29 and matrix controller 37. A reset signal generator 41 is provided, which generates a reset signal to reset the level discriminator 40 and reset the mode discrimination output when the RF signal of the reproduced audio information disappears. Regarding the switching circuit 28, S ₁ to _{S 4}
It consists of four switches, and switch _S1 turns the output line 30 of the LPF 24 on and off.
Output of LPF26 and line 31 by switch _S4
On and off are performed respectively. Also, Switch S ₃
The output of the detector 27 and the line 31 are turned on and off, and the switches S ₂ and S ₃ turn the output of the detector 27 on and off.
The output of the line 30 is turned on and off. In addition, DOS (dropout sensors) 42 to 44 are provided to detect dropout, and these detect the presence or absence of a signal level at each input of the detectors 27, 21, and 22 to identify the occurrence of dropout. are doing. A switch controller 29 is controlled by the sensor output of each DOS, and controls on/off of each switch of the switching circuit 28. In this configuration, the audio information extracted by the LPF 18 is separated into two channel information by the BPFs 19 and 20. That is, the main carrier is separated into a 2.3MHz component and a 2.8MHz component. Now, we will discuss playback when MPX stereo mode information is recorded on the video disc.
First, the state of the switch 23 is controlled by the user's selection. For example, when the first Japanese language stereo using the first channel and the second channel shown in FIG. 2 is selected, the switch 23 switches the detector 2
1 output is selected. Further, the switching circuit 28 is controlled so that the switches S ₁ and S ₃ are on and the other switches S ₂ and S ₄ are off. The switch control of this switching circuit 28 is performed by the discriminator 4 that discriminates the level of the subcarrier signal.
Automatically done by outputting 0. That is,
This is done by determining that the MPX stereo mode level is set. Main channel signal (L+R) of stereo information from the first channel and the second channel
is extracted by the LPF 24, and the subchannel signal (LR) is extracted by the BPF 25 and subjected to FM detection by the detector 27. (L+R)
The signal is output on line 30 via switch _S1 , and the (LR) signal is output on line ₃₁ via switch S3 and applied to matrix circuit 36, respectively. Since the MPX stereo mode is determined by the level discriminator 40 and the corresponding mode output is generated, the matrix controller 3
7, both (L+R) and (LR) signals are subjected to addition and subtraction processing to derive left and right channel stereo signals of the first two languages, respectively. When selecting the second language stereo based on the third and fourth channel signals in FIG. The switch 23 is controlled by the control signal to select the output of the detector 22. Switching circuit 2
8 and the matrix circuit 36 are the same as in the first Japanese language stereo described above. Therefore, the main carrier 2.8 MPH audio information is selected at switch 23 and the (L+R) and (LR) signals are routed to lines 30 and 31, respectively. Then, by matrix processing, left and right channel stereo signals in the second language are obtained. Next, a case will be described in which independent signals of four languages are recorded on a video disk as channels 1 to 4 in FIG. 2. In this case, since each channel has independent content, performing matrix processing will result in loss of compatibility with existing regenerators that do not have subchannel reproducing functions. Each channel signal is multiplexed and recorded without being separated. In this case, since it is MPX monaural mode,
The subcarrier level is equivalent to 45%, and the discriminator 40 detects this and controls the matrix circuit 36 so that it does not perform addition/subtraction processing. At this time, the switch 23 is activated by a control signal corresponding to the operation of the external audio signal selection switch by the user.
Then, the switching circuit 28 is switched, and it becomes possible to listen to any one of the first to fourth languages. For example, to select the first language, the switch 23 selects the output of the detector 21, and the switching circuit 28 selects the output of the detector _{21 .}
All you have to do is turn on one and turn off the other. The selection of other channels can be considered in the same way. The switching status of each switch in such a case is shown in the table.

[Table] Dropout is a phenomenon in which the signal on the recording track cannot be read due to scratches or dust on the video disk, and it occurs in a relatively short period of time. The lack of information due to this dropout can be detected in DOS42-44
As shown in the bottom column of the table above, the switches S ₁ to _{S 4} of the switching circuit 28 are all turned off as shown in the bottom column of the table above, and the hold output immediately before the dropout caused by the hold capacitors 32 and 33 is sent out to compensate. ing. That is, in a normal playback state, the on/off state of each switch S ₁ to _{S 4} is determined by one of the modes as described above, but during the dropout period, all switches S ₁ to _{S 4} are set regardless of the mode. Forced off, dropout compensation is performed by capacitors 32 and 33.
This is done by The input impedance of the amplifiers 34 and 35 is made sufficiently large, and the capacitors 32 and
33 is prevented from discharging.
In addition to the period during which the dropout is occurring, each switch _S1 to _S4 is turned off for a short period after the dropout ends to compensate for the dropout. This is to prevent the occurrence from being transmitted to the output. For this purpose, the switch controller 29 is configured to output a control signal for a slightly longer period than the dropout occurrence period. The features and advantages of the configuration shown in FIG. 5 will be described below. First of all, it is characterized by providing only one reproduction and demodulation circuit system for the recorded information of the two newly added subchannels, which can be shared by switching it with the switch 23. The system configuration can be simplified, making it possible to reduce costs and facilitate integration. Furthermore, by using a common circuit, the reproduction characteristics such as the sound quality of the two sets of stereo signals (including foreign language signals) are the same, and the characteristics of each channel do not change due to changes over time or temperature. There are advantages. The second configuration feature is related to the first configuration feature, but is newly added.
When providing only one reproducing demodulation circuit system for the recorded information of two subchannels and allowing it to be shared, the input changeover switch 23 to this common demodulation circuit system is
The main channel is not located at a position where only the sub-channels are selectively switched, but at a position where the main channel is also switched at the same time as shown in FIG. When a subcarrier regenerative demodulation circuit system is shared, a commonly considered switching configuration is to provide a switch that only switches between the two subchannels at the input stage of the regenerative demodulation circuit system, and to switch between the two main channels as follows: This is a configuration in which the switching is performed inside the switching circuit 28 of the stage. However, such a configuration is undesirable because the number of switches increases and the control of the switches becomes complicated. Therefore, the above-mentioned configuration shown in FIG. 5 is adopted to reduce the number of switches. The structural feature of FIG. 3 is in the dropout compensation circuit, in which the switches S ₁ to _{S 4} of the channel selection switching circuit 28 are used as a part of the dropout compensation circuit, and the dropout compensation capacitors 32 and 33 are used as a part of the dropout compensation circuit. is shared between the main channel and subchannel, simplifying the circuit. The fourth feature is the program mode (MPX stereo, MPX monaural, NO-
Change it for each mode of MPX and record it.
The point is that this subcarrier level is discriminated in the reproduction system to determine the recording mode. By doing so, there is an advantage that there is no need to specially insert an identification signal indicating the recording mode during recording. In the circuit configuration shown in FIG. 5, only a part of the 4-channel multiplexed audio information, that is, only two channel signals, is selectively output, but a 4-channel signal output adapter as shown in FIG. It is conceivable that all 4-channel multiplexed information can be reproduced by separately adding . That is, as shown by the dotted line in FIG.
The reproduced RF signal by the LPF 18 is derived from the terminal 45, and the recording mode identification signal by the level discriminator 40 is derived from the terminal 40.
In the adapter shown in FIG. 6, BPFs 60 and 61 for inputting the reproduced RF signal are provided to select and extract the main carriers 2.3MHz and 2.8MHz. Each output of BPF 60, 61 is detected by FM detector 62, 63, and LPF 64, 6
5, the main channel signals are respectively extracted. In addition, the output wave BPF6 of each detector 62, 63
6 and 67, the signals near the subcarriers are extracted, and the subchannels are detected in the next stage detectors 68 and 69. These main channels and sub-channels are applied to the channel signal processing circuit 70, and the combination processing of each channel signal is performed in accordance with the recording mode discrimination signal derived from the output terminal 46 of the circuit device shown in FIG. 5 mentioned above. . Then, four channel outputs are obtained from the output terminals 71 to 74, respectively. Further, for example, arbitrary signals may be output from the output terminals 71 and 73 according to a user's command, and if necessary, all channels of broadcasting in four countries may be output, or a specific It is also possible to output only the channel. Therefore, in the signal processing circuit 70, each combination of these output signals can be appropriately selected by an external select signal. Furthermore, it goes without saying that a structure may be adopted in which all four channel signals are simply led out to the respective output terminals 71 to 74 without introducing the recording mode discrimination signal from the circuit shown in FIG. In addition, as another example, only normal 2-channel playback, that is, NO-MPX mode playback, is possible.
Audio RF information may be introduced from a VDP (video disc player) and input to the adapter shown in Figure 6, so that all 4-channel disc playback can be obtained from this adapter, and the adapter can only play subchannels. It may be configured as follows. By doing this, all channels can be played back simultaneously, and the number of circuits in the VDP itself can be reduced. In addition, since only the audio information signal from which video information and the like having components around 10 MHz have been removed is supplied to the outside from the external supply terminal (45 in Figure 5), unnecessary radiation may cause interference with other external equipment (TV). radio, etc.) will be eliminated. In the above example, there are two additional
Although all subchannels are FM processed and recorded on the recording disk, they may also be processed and recorded using AM (amplitude modulation) processing. Therefore, in this case, the modulators 9 and 10 in the recording system of FIG.
It is clear that the detectors 27, 68, and 69 in the reproducing system of FIGS. 5 and 6 become AM detectors. Here, when multiplexing subchannels, if the subcarrier is subjected to AM or FM processing and then the main carrier is subjected to FM processing, in other words, which method has better characteristics during playback: FM-AM method or FM-FM method. Consider using Figures 7 and 8. The amplitude characteristics of the reproduction system of FIG. 5 with a BPF of 19.20 are as shown in FIG. 7A, and the group delay characteristics are as shown in FIG. 7B. In other words, when it is necessary to maintain a certain level of amplitude characteristics, the flat part of the group delay characteristic has to become narrow, and therefore, as shown in Figure B, the flat part of the group delay characteristic has a narrow band of ±75KHz. It's summery. Here, the frequency spectrum that also takes into account the upper and lower sidebands when the main carrier _C receives FM modulation and reaches a certain instantaneous frequency _C1 is calculated as follows.
Figure 8A when drawn over the group delay characteristic of BPF
It will be like this. In Figure A, for simplicity, FM
In the case of the FM method, only the primary sideband is considered, so as an example of the FM-AM method, we show the frequency spectrum when a monotone signal is balanced modulated and then further FM _modulated.1 , ₂ indicate the upper sideband, and ₃ and ₄ indicate the lower sideband. When the instantaneous frequency _C1 of the main carrier _C reaches the upper limit of the flat part of the group delay characteristic, the upper sideband ₁ ,
₂ will both be subject to phase and amplitude fluctuations.
Therefore, if each frequency component is expressed as a vector at this time, it will look like Figure B, with upper sidebands ₁ and ₂
will be shifted from the normal position (shown by the dotted line). For this purpose, the composite wave of both sidebands ₁ and ₂ is
₁₂ also deviates from the normal position shown by the dotted line. Then,
Both the phase and amplitude of the total composite vector (not shown) of the main carrier _C1 and composite waves ₁₂ and ₃₄ (combined waves of lower side bands ₃ and ₄ ) change. Then,
The FM-AM method has a large negative effect on the reproduced output, but the FM-FM method has the advantage that it is not affected by amplitude fluctuations of the subchannel carrier reproduced by the first detector. Furthermore, in reality, the detection characteristics of the FM detectors 21 and 22 (see FIG. 5) have frequency characteristics as shown in FIG. C, and do not exhibit linearity over the entire range. Therefore, if the main channel is significantly modulated by passing through such a detector, the amplitude characteristics of the subchannels will be affected. In this case, FM—
The AM system will be more adversely affected than the FM-FM system. Therefore, FM-FM
If this method is used, the reproduction characteristics will be better. Audio multiplex information recording mode (MPX stereo,
In each of the above examples, a method was used in which the subcarrier level of the subchannel was changed in advance according to each mode in order to indicate each mode (MPX monaural, etc.). It is also conceivable to code an identification signal for identifying the recording mode in advance in a portion that does not affect the video information, and record the code in a time-axis multiplex manner together with a frame number representing the address information of the playback track. In this case, the rectifier 38, LPF 39, level discriminator 40 and reset signal generator 41 in the circuit system of FIG. 5 are no longer necessary.
Instead, a recording mode discriminator may be added that detects the recording mode identification code signal from the output of a video detector (not shown) and generates a control signal. Here, when using an adapter as shown in FIG. 6, when the operation mode of the playback system shown in FIG. 5 is in a special mode, such as a mode such as stall playback or double speed playback, the adapter will not operate in playback mode to prevent noise generation. It is desirable to avoid this. Therefore, the circuit system shown in FIG. 9 can be considered. That is, the reproduced RF signal from the pickup 17 is input to an audio processing circuit 90 and a video processing circuit 91. The audio processing circuit 90 is the same as the audio demodulation system shown in FIG. 5, and selectively reproduces only two channel signals out of four channel multiplexed information. This audio processing circuit 90
The output of the input stage LPF 18 (see Fig. 5) is connected to the output terminal 45 via the ATT (attenuator) 92.
and connect it to the playback RF of the adapter 94 in Figure 6.
Use as input. On the other hand, the video output from the video processing circuit 91 is input to a control circuit 93 such as a microcomputer, and the attenuation state of the ATT 92 is controlled by the control output of the control circuit 93.
Further, the control circuit 93 receives various operation mode command signals from the keyboard 95, and controls the operation mode of the regenerator and also controls the attenuation state of the ATT 92. Here, in the case of a video disc in which the identification signal of the multiplexed recording mode of video information is coded into the video information and inserted and recorded as described above, NO--
In MPX mode, playback is not required when using the adapter 94 that only plays subchannel signals, so the control circuit 93 detects this code indicating NO-MPX mode from the video signal output and attenuates the ATT92. The amount is controlled to be large (or almost infinite). Therefore, the audio RF signal level at the input of the adapter 94 is extremely low (or almost zero).
Thus, the above objective is achieved. Furthermore, since it is preferable that the regenerator side performs so-called muting of audio information during predetermined modes such as the above-mentioned special playback mode, the control circuit 93 determines the operation state of the keyboard 95 and selects these special playback modes. The period ATT92 is controlled and mutating is performed in the same way. By doing this, in a playback mode where the adapter 94 may perform incorrect playback due to a disturbed playback RF signal, the level of the playback RF signal sent to the adapter is attenuated and the adapter playback is stopped. Erroneous playback can be prevented.
In addition, since the RF signal level at the input stage of the adapter is used to control whether or not the adapter can perform demodulation, the connection between the regenerator and the adapter is simply one audio information transmission path. The cost of the connector is low, and there is no need to worry about incorrect wiring connections. Furthermore, since the adapter only determines the presence or absence of the RF signal level, there is no need to use special logic circuits or microcomputers, and the adapter is inexpensive. No malfunctions occur. FIG. 10 is a block diagram showing another example of muting in an adapter, in which a reproduced RF signal A input to the adapter is detected by an envelope detector 100. The detected output B becomes a pulse-like waveform C in the waveform shaper 101. This pulse C triggers a retriggerable MMV (monostable multivibrator) 102, and its Q output D becomes one input of a two-input NAND gate 103 and also becomes a trigger input of another triggerable MMV 104. The output E of this MMV104 is the other input of the gate 103, and this gate 1
The output F of 03 is used as a muting signal. FIG. 11 shows operating waveforms of signals of each part of the circuit of FIG. 10, and A to F correspond to signals A to F of each part of FIG. 10. As mentioned above, when the playback device is in a special mode other than the normal playback mode, such as still playback or double speed playback, the adapter should not play audio information in the same way as in the normal playback mode. As such, the case of steel playback will be explained, for example. In the case of still playback, the pick-up operates to skip recording tracks on the video disk at regular time intervals and always track the same track, so playback starts at the moment of this track jump.
The RF signal disappears. Since this occurs periodically, the reproduced RF signal becomes as shown in Figure A. Since the extinction in this case occurs more noticeably than in the case of other dropouts or noises, the envelope detection output will be as shown in Figure B. If this is shaped by the waveform shaper 101 having a level comparator function, the pickup will be reduced. A pulse train generated synchronously every time the track is jumped is obtained as shown in Figure C. In this case, if the output pulse width of the MMV 102 is selected to be slightly larger than the pulse period in Figure C during jump, the Q output of the MMV 102 will be as shown in Figure D. Therefore, since the Q output of the MMV 104 is as shown in Figure E, the NAND gate outputs of the outputs D and F of both MMVs 102 and 104 are as shown in Figure F, and a low level output is obtained during the steal operation period. It can be a muting signal. 1st
In the example shown in FIG. 0, if a pulse width detection circuit that outputs a pulse only when a predetermined pulse width is input is added to the front stage of the MMV 102, even more accurate operation will be possible. In addition, the output pulse width of MMV102 is MMV10
By making it slightly smaller than that of 4, the first
This makes it possible to mask dropouts that occur sporadically as shown in the right-hand portion of Figure 1. Even in the playback mode in the forward and reverse directions at a predetermined double speed, if the output pulse widths of the MMVs 102 and 104 are appropriately set, a muting signal is similarly generated during the playback mode. The purpose can be achieved by blocking or attenuating the playback output of the adapter using this muting signal. By doing this, it is possible to generate a muting signal only from the reproduced RF signal without receiving any reproduction mode information from the regenerator side, so that various effects similar to those described in the example of Fig. 9 can be obtained. occurs. The modes of four-channel multiplexing of audio information are: (1) The first channel and the second channel are in stereo mode; the second channel and the fourth channel are in stereo mode; (2) the first channel and the second channel are in stereo mode. , 3rd and 4th channels are in 2-language mode; (3) 1st and 2nd channels are in 2-language mode, 3rd and 4th channels are in stereo mode; (4) All channels are in independent 4 However, if we consider the existing 4-channel system, matrix 4-channel system, SQ encode 4-channel system, etc., the signal may become an 8-channel signal even though it is actually 4 channels. Of course, it can also be applied. In general recording and reproducing systems, a so-called noise reduction device such as a signal compression/expansion device is used in order to improve the characteristics of the reproduced signal, and it is preferable to use the noise reduction device in the above-mentioned system as well. In this case, the signal compression/expansion device disclosed in Utility Model Application No. 57-129585 by the applicant of the present invention or the same
It is preferable to use the noise reduction method disclosed in the specification of No. 163320. In the above example, a video disk was described, but the present invention can be applied not only to general recording media but also to a transmission system in which multiplexed information is frequency-converted and transmitted/received via a signal transmission path. As described above, according to the present invention, it is possible to transmit a new audio channel signal using substantially the same band as the main carrier band for audio information on a recording disk according to the prior art, and to transmit a new audio channel signal on the playback side. Since it is sufficient to provide only one demodulation system, the circuit system can be simplified, and integration can be facilitated, resulting in low cost. In addition, by using a common demodulation circuit, the reproduction characteristics such as sound quality of two sets of stereo signals are the same,
This has the advantage that differences in characteristics between channels do not occur due to changes over time or temperature.

[Brief explanation of drawings]

Figure 1 is a diagram showing the recording frequency spectrum of a video disc, Figure 2 is a block diagram of the multiplex recording system, Figure 3 is a diagram showing the frequency spectrum for subchannel multiplexing, and Figure 4 is the frequency of the subchannels. A diagram explaining how to select a subcarrier frequency for conversion, Figure 5 is a block diagram of a reproduction method for a multiplex recording medium, Figure 6 is a block diagram of a reproduction adapter, and Figures 7 and 8 are subchannel modulation. Figure 9 is a block diagram illustrating a mode of signal exchange between the regenerator and the regenerator, and Figure 10 is a block diagram illustrating a method for determining the operating mode of the regenerator in the regenerator. 11 are diagrams showing operating waveforms of each part of the circuit block of FIG. 10. Explanation of symbols of main parts, 9, 10...FM/
AM modulator, 11, 12, 13...FM modulator,
17... Pick up, 18, 24, 26...
LPF, 19, 20, 25... BPF, 21, 22,
27...Detector, 23...Switch circuit, 28...
...Switching circuit, 32, 33... Hold capacitor, 36... Matrix circuit, 40...
...Level determiner, 42-44...DOS, 94...
…Playback adapter.

Claims (1)

[Claims] 1. Two subcarriers of the same frequency are each modulated by two subchannel signals to obtain two modulated subcarrier signals, and each of these modulated subcarrier signals and two main channel signals are superimposed, respectively. These two sets of superimposed signals are used to frequency-modulate the main carriers of two different frequencies to obtain two frequency-modulated main carriers, and these frequency-modulated main carrier signals are used to record on a recording medium, and for reproduction, extracting the frequency modulated main carrier signal from the read signal from the recording medium by frequency separation; detecting the extracted frequency modulated main carrier signal by separate frequency detection means to demodulate the two sets of the superimposed signals; selectively selecting one of the two sets of demodulated superimposed signals, separating the main channel signal and the modulated subcarrier signal from the selected superimposed signal, and separating the subchannel signal from the separated modulated subcarrier signal. A method for recording and reproducing multiplexed information by demodulating it.