JPH0310161B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing apparatus characterized in that an audio recording signal is multiplexed recorded with a video recording signal, for example, as an FM modulated signal.

In general magnetic recording and reproducing devices (hereinafter abbreviated as VTR), in recent years, in order to increase the recording density on magnetic tape, means for improving the playback image quality and sound quality have been developed. As one of the means for achieving this, there is a proposal to mix the audio recording signal with the video recording signal as an FM modulated signal, and to multiplex record the signal onto a video track. Magnetic tape manufacturing technology has also made rapid progress, and metal tapes, vapor-deposited tapes, and other tapes with excellent short wavelength recording and reproducing properties have emerged, and there are proposals to use them in VTRs.

First, an example of a recording method for multiplex recording an audio signal onto a video track will be explained with reference to FIGS. 1 and 2. FIG. 1 is a block diagram of the recording signal system, in which 1 is a luminance signal recording system, 2 is a chromaticity signal recording system, 3 is an audio signal recording system, 4 is an adder, 5 is a recording equalizer, 6 is a recording amplifier, 7 is the recording head;
8 is a magnetic tape.

The luminance signal component of the video signal inputted from the video signal input terminal 10 is extracted by an LPF (low pass filter) 11 having a cutoff frequency of approximately 3 MHz, and the luminance signal component is extracted by an FM modulator 12 for luminance FM modulation having a frequency band of approximately 4±3 MHz. It becomes a signal. After that 1~
A HPF (high pass filter) 13 with a cutoff frequency of 1.4 MHz removes frequency components that overlap with the frequency band of the chromaticity recording signal, which will be described later. Remove the frequency component and adder 4
Add to.

On the other hand, the signal input from input terminal 10 is approximately
A chromaticity signal component is extracted by a BPF (band pass filter) 21 having a passband of 3.58±0.5MHz, and converted into a chromaticity recording signal having a frequency band of approximately 0.6 (~0.7) ±0.5MHz by a frequency converter 22. be done. After that, LPF2 has a cutoff frequency around 1.4MHz.
3, unnecessary high frequency components are removed, and the frequency components are further removed by a trap circuit 24 having an attenuation pole near the audio recording signal carrier frequency, and then added to the adder 4.

Further, the audio signal inputted from the audio signal input terminal 30 is converted into an audio FM modulated signal having a frequency band of approximately 0.2±0.1MHz by the FM modulator 31. After that, LPF3 with a cutoff frequency of about 1.4MHz
After removing unnecessary high frequency components in Step 2, the signal is added to an adder 4.

These three types of recording signals are mixed and summed by an adder 4, and then a recording equalizer 5 emphasizes the low frequency component where the recording capacity of the magnetic tape is large.
The data is applied to the recording head 7 via the magnetic tape 8 and recorded on the magnetic tape 8.

FIG. 2 illustrates the recording current spectrum flowing through the winding of the recording head 7. In FIG. On the vertical axis in the figure
0 dB is the recording level of the luminance FM carrier wave, and is also the saturation recording level of this carrier wave (that is, the recording level at which the maximum output is obtained during reproduction). In order to avoid cross-modulation interference in the tape/head system for three types of recording signals, when using the currently widely used oxide tape, the signal level of the chromaticity recording signal carrier wave is approximately 10 to 14 dB higher than that of the audio FM carrier wave. It is normal to lower it by about 10dB further.
In other words, the chromaticity signal and the audio FM signal are recorded on the magnetic tape using the luminance FM carrier wave recorded in saturation as a bias signal. Furthermore, as explained in FIG. 1, the recording signal system includes 13, 23, 3
Since filters 2 and trap circuits 14 and 24 are combined, the spectra of the three types of recording signals do not overlap and interfere with each other.

Note that the HPF 13, trap circuit 14, and
combination, as well as LPF23 and trap circuit 2
The order of the combinations of 4 is completely arbitrary. Since the luminance signal recording system 1 and the audio signal recording system 3 are FM modulation systems, they actually include AGC, pre-emphasis, a clip circuit for preventing overmodulation, etc., but these are irrelevant to the essence of the present invention described below. Because there is no, all
It was considered to be included in the FM modulators 12 and 31. The chromaticity signal recording system 2 actually includes an emphasis for the burst portion, a sub-carrier wave generation circuit for frequency conversion, etc., but they were all included in the frequency conversion circuit 22 in the same way. As described above, video signals and audio signals can be multiplexed recorded on the same video track.

Next, we will explain recent magnetic tapes for VTRs, with particular emphasis on their single-frequency signal transmission characteristics. So-called oxide tapes, which have conventionally used γ-Fe ₂ O ₃ as a main component of magnetic powder, are still the mainstream of magnetic tapes. For several years now, metal tapes using Fe powder have also been produced at the prototype level. Currently, the magnetic layer thickness for VTR tapes is 4 to 4 for both oxide tape and metal tape.
Since they almost match at about 5 μm, the transmission frequency characteristics of the recorded and reproduced signals are almost the same. However, the absolute value differs due to differences in residual magnetic flux density, and metal tape has a higher resistance than oxide tape.
About 3 to 6 dB high. On the other hand, just recently Fe,
Vacuum-deposited tapes have appeared in which Ni, Co powder, etc. are vacuum-deposited onto a tape base. Unlike the above two types of magnetic tape, this tape does not have a binder to fix the magnetic powder in the magnetic layer, so it can be expected to have an extremely high density recording ability in the future. However, currently, due to technical constraints, the magnetic layer thickness can only be reduced to around 0.2 μm, and the transmission characteristics of recorded and reproduced signals are unique compared to oxide tapes, metal tapes, etc. . In other words, in the high frequency region (short recording wavelength), the effect of the high density of magnetic powder in the magnetic layer (100%) appears, and the level of the reproduced signal is high, but conversely, in the low frequency region (long recording wavelength), the effect is high (100%). The level of the reproduced signal is low due to the effect of the thin magnetic layer.

These matters will be shown in more detail using FIG. This figure shows the calculation results of the transmission frequency characteristics and absolute values of a single frequency signal in a general-purpose VTR. 0 dB on the vertical axis is the 4 MHz playback output of a certain oxide tape that was the subject of calculation. Based on this, the characteristics of each tape can be summarized as follows.

1. There is almost no difference in transmission frequency characteristics between metal tape and oxide tape. The absolute value of the playback output is about 5dB higher in the former. (The higher the frequency, the slightly wider this difference is because metal tape has smaller self-demagnetizing loss at short wavelengths.) 2. Vapor-deposited tape has transmission frequency characteristics that are lower than those of the other two types of tape. It's completely different. The absolute value of the playback output is
It is 4 to 5 dB higher than metal tape in the frequency range above 4MHz, but lower than metal tape in the frequency range below 1.2MHz, approaching oxide tape.

From FIG. 3, it is clear that the magnetic layer thickness has a decisive influence on the frequency characteristics of signal transmission.

By the way, considering the future of VCRs, it would be convenient for general users to be able to use the various types of magnetic tapes mentioned above interchangeably. In other words, 4~5M for metal tape, vaporized tape, etc.
As you can see from the fact that the Hz playback output is higher than that of oxide tape, you can expect more beautiful playback images. On the other hand, since mass production technology for oxide tape has already been accumulated over many years, it can be expected to be available at a lower price. In other words, it is possible to meet the diverse needs of users.

However, there is one problem here. First, the frequency band of the luminance recording EM signal is approximately 4±3M.
Hz, and that of the audio recording FM signal is approximately
He explained that it is around 1.2MHz. Oxide tape and metal tape have almost the same frequency characteristics, so if you maintain a balance between the playback image quality and playback quality of one tape, you can also maintain this balance with the other tape. However, in the case of vapor-deposited tape, the brightness is lower than that of the other two types of tape.
Although the playback level of the FM signal increases, the audio FM
The signal playback level does not increase and the balance between image quality and sound quality is lost. The same thing is 0.6±0.5M
The same can be said of the level ratio during reproduction between a color signal having a band in Hz and the luminance FM signal, as well as the level ratio during reproduction between the lower sideband wave of the luminance FM signal and the carrier wave. If it is desired to use these tapes interchangeably, it is necessary to devise a method that allows the reproduction level ratio of each recorded signal to be adjusted for vapor-deposited tapes as well as for other tapes.

The purpose of the present invention is to solve problems such as changes in the balance between sound quality and image quality during playback, and to correct differences in frequency characteristics caused by differences in magnetic layer thickness using low-cost circuit means. The present invention provides a recording equalizer circuit that performs the following functions.

The present invention improves the recording level of the FM modulated signal to be recorded in both the luminance signal recording system and the audio signal recording system.
and a recording equalizer circuit that can change the frequency characteristics given to this for each magnetic tape used, so that no matter what characteristics the magnetic tape is used, the optimum recording conditions can be given to that tape. do. After passing through this recording equalizer circuit, each recording signal is mixed and added and recorded on a magnetic tape.

The recording equalizer circuit can be placed anywhere after each signal has been converted into an FM modulated signal, but it is best to place the recording equalizer circuit in front of an adder that mixes and adds the FM modulated signals of both brightness and audio. Explain the reason for placing it in

If you want to maintain the same balance between image quality and sound quality during playback for all tapes, for example, the brightness FM carrier frequency of the metal tape (for example, 4MHz)
What is necessary is to match the difference in playback output (frequency characteristics) between the FM tape and the audio FM carrier frequency (for example, 1.2 MHz) with that of the vapor-deposited tape. From Figure 3, the former is
5.5dB, and the latter is 1.5dB, so all you have to do is change the recording equalizer circuit characteristics to compensate for the 4dB difference. In this way, the level ratio between the sideband wave of the luminance FM signal and the carrier wave during reproduction can also be compensated, which is convenient. Such a recording equalizer circuit can be placed after the mixed addition. But there's one problem.

In general, the recording level ratio between the audio FM signal and the brightness FM signal is not decided by considering only the level ratio during playback as it is now, but by recording a mixture of both signals. The magnitude of the resulting cross-modulation beat must also be considered.
This beat occurs most frequently in the luminance signal in a reproduced image. When the S/N ratio of the reproduced image is poor, it is difficult to see because it is hidden by noise, but it becomes easier to see when the reproduction level of the luminance FM signal is high and the S/N ratio is good, especially when using vapor-deposited tape. be.

Therefore, as compensation during recording, it is likely that a value slightly smaller than the above-mentioned 4 dB will be optimal. On the other hand, it is preferable to leave it at 4 dB in order to match the ratio between the sideband and carrier waves of the luminance FM signal. In other words, in order to suppress the beat disturbance that becomes more visible when the playback level of the brightness FM signal is high, the audio
In order to lower the playback level of the FM signal and to make the balance between the carrier wave and sideband waves of the brightness FM signal common for all tapes during playback, the sideband waves of the brightness FM signal and the audio FM signal whose frequencies are close to each other are The amount of compensation must be different. Luminance
Since it is not possible to give different frequency characteristics to the same frequency component when the FM signal and the audio FM signal are mixed, it is necessary to provide separate recording equalizer circuits for the luminance FM signal and the audio FM signal before mixing. There is.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a block diagram showing the configuration of the magnetic recording/reproducing apparatus of the present invention. Note that, unlike the conventional example shown in FIG. 2, only constituent elements directly related to the present invention are shown. In FIG. 4, 9 is a luminance signal recording system, 1
0 is an audio signal recording system. The luminance FM signal inputted from the input terminal 90 passes through the HPF 91 and trap circuit 92, which have the same functions as the HPF 13 and trap circuit 14 described in the conventional example shown in FIG. 1, and is added to the first recording equalizer 93. . Here, the optimum frequency characteristics are switched and applied to the luminance FM signal according to the frequency characteristics of the magnetic tape used. Next, in the second recording equalizer 94, the brightness FM
The signal level is switched and set to a level that allows saturation recording for each magnetic tape used. After that, it is added to adder 4. On the other hand, the audio FM recording signal input from the input terminal 100 is transmitted to the LPF 100, which has the same function as the LPF 32 described in the conventional example shown in FIG.
and is added to the third recording equalizer 102.
Here, the ratio of the carrier wave level during playback to the carrier wave level during playback of the luminance FM signal, and the level of the cross-modulation beat that appears in the playback image are considered, and the optimum value is determined for each magnetic tape used. Switch and set the level to obtain a suitable recording level. After that, it is added to adder 4. These signals mixed and added by the adder 4 are recorded on the magnetic tape 8 via the recording amplifier 11 and the recording head 7. In addition,
The arrangement order of the HPF 91, the trap circuit 92, and the first and second recording equalizers 93 and 94 is completely arbitrary. The same applies to the LPF 101 and the third equalizer 102. Further, since the second recording equalizer 94 alone determines the recording level of the recording FM signal, it may be placed after the adder 4, or may be included in the recording amplifier 11, for example. Even if this is done, it does not depart from the spirit of the present invention.

Next, an embodiment will be described with reference to FIG. 5, which further shows a specific circuit diagram of the present invention. Note that the HPF 91, trap circuit 92, and LPF 101 shown in FIG. 4 are omitted from this figure. 95 is the brightness FM signal, 103
is the audio FM signal input terminal. Input terminals 931, 941, 942, 1021, and 1022 are input terminals for control signals whose levels change depending on the magnetic tape used. When using oxide tape, only 931 is low, the others are high, and when using metal tape, all are input terminals. level is Low, only 931,941,1021 when using vapor deposition tape
It is assumed that the setting is High, and the others are set to Low.

The first recording equalizer 93 is a transistor Q ₁
The emitter is grounded through a resistor R ₂ and a series circuit consisting of a bypass capacitor C, an inductor L, a resistor R ₃ , and a transistor Q ₂ . Transistor Q ₂ is ON only when vapor-deposited tape is used, so
Compared to when using other tapes, the level of the lower sideband of the luminance FM signal is emphasized relative to the level of the carrier wave. The ratio is inductor L, resistance R ₃
By appropriately adjusting the value of , the level ratio between the lower sideband wave and the carrier wave at the time of equalization will not vary depending on the magnetic tape used.

The second recording equalizer 94 is a transistor Q ₃
The signal voltage at the emitter is the same voltage when using the metal tape,
When vapor-deposited tape is used, the voltage is divided by resistors _R5 and _R6 ,
When an oxide tape is used, the voltage is divided by resistors R ₅ , R ₆ , and R ₇ and sent to the adder 4. In each case, the resistance values R ₅ to _{R 7} may be selected so that the signal voltage is at a level that saturates recording on the magnetic tape used.

The same may be applied to the third recording equalizer 102. That is, the values of the resistance values R ₉ to R ₁₁ may be selected so that the level of the audio FM signal sent to the adder 4 is the optimum level in view of the sound quality during reproduction, the cross-modulation beat of the reproduced image, etc.

The characteristics of the first recording equalizer are designed to remain the same when using an oxide tape and when using a metal tape, but they may be switched if necessary. Furthermore, the gains of the second and third recording equalizers 94 and 102 are set to increase in the order of metal tape use, vapor deposition tape use, and oxide tape use, but this is also not a necessary condition. The operation of each recording equalizer may be set so as to fulfill the purpose described above.

Furthermore, as described above, the second recording equalizer may be configured to be included in the recording amplifier 11. For example, a tapped transformer may be provided between this and the recording head 7, and the taps may be switched for each magnetic tape used. The gain may also be switched.

Also, although the chromaticity signal recording system is omitted in Figures 4 and 5, if it is present, a fourth equalizer is provided in the same way as the audio signal recording system, and the recording level is switched for each magnetic tape used. Just do it.

As explained above, the present invention interchangeably uses multiple types of magnetic tapes that have different playback outputs and frequency characteristics due to various factors such as differences in magnetic layer thickness, and uses a luminance signal as an FM modulation signal. In addition, in a VTR that records the audio signal as an FM modulated signal and mixes and adds both, there is a recording equalizer that switches its characteristics depending on the magnetic tape used for both the luminance signal recording system and the audio signal recording system before mixing and adding. The idea is to establish a

As a result, no matter what kind of magnetic tape is used, the balance between playback sound quality and image quality is maintained for each tape.
Optimum recording conditions can be set in consideration of cross-modulation beats appearing in reproduced images.
Moreover, this can be realized at low cost by simply changing the circuit configuration.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example of a recording signal system, Fig. 2 is a characteristic diagram showing the recording current spectrum, Fig. 3 is a signal recording/reproducing frequency characteristic diagram, and Fig. 4 is a characteristic diagram showing the recording current spectrum.
The figure is a block diagram showing one embodiment of the magnetic recording/reproducing apparatus of the present invention, and FIG. 5 is a circuit diagram showing a specific embodiment of the present invention. 93...first recording equalizer, 94...second
recording equalizer, 102...Third recording equalizer.

Claims (1)

[Claims] 1. A frequency modulation circuit for brightness signals that frequency modulates a brightness signal; A frequency modulated brightness signal output from the frequency modulation circuit for brightness signals is supplied, and a frequency modulation circuit for frequency modulating a brightness signal is provided, and A brightness signal equalizer circuit that switches frequency characteristics according to the type of magnetic tape used for recording, and a frequency modulated audio signal that frequency modulates the audio signal and outputs a frequency modulated audio signal in a frequency band lower than the frequency modulated brightness signal. a frequency modulation circuit for audio signals; an equalizer circuit for audio signals to which the frequency modulated audio signal is supplied and switches the recording level of the frequency modulated audio signal in accordance with the type of magnetic tape; and output signals of the two equalizer circuits. 1. A magnetic recording device comprising: a synthesis circuit for synthesizing; and a magnetic head for recording on the magnetic tape using an output signal of the synthesis circuit. 2 The brightness and audio signal equalizer circuit compensates for the difference in reproduction frequency characteristics that differ depending on the type of magnetic tape, and is useful when a magnetic tape with a high reproduction level of frequency modulated luminance signals is used for recording. 2. The magnetic recording device according to claim 1, wherein the compensation by the audio signal equalizer circuit is slightly smaller than the compensation by the luminance signal equalizer circuit.