JPS61206970A - Video signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain stable frequency characteristic of video signals at all times by recording signals having frequency shift that sufficiently enters lower side wave zone and higher side wave zone by introducing an inspection signal larger in amplitude than video signals to an FM modulator and making amplitude (AM) detection before FM demodulation. CONSTITUTION:A signal larger in amplitude than video signals generated in an inspection signal generator 18 is introduced to an FM modulator 11 through a switching unit 19 and FM modulated. As amplitude of the inspection signal is large, it is modulated to large frequency range. Accordingly, the signals modulated by the inspection signal are recorded on a magnetic tape including lower side wave zone and higher side wave zone sufficiently. When an area in which the signals are recorded is reproduced, if difference is caused between the lower side wave zone and higher side wave zone, difference is caused in amplitude of the reproduced signals. Frequency characteristic of video signals can be estimated by detecting the difference by an AM detector 20.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video recording and reproducing device that records a video signal using FM (frequency modulation) and is capable of detecting differences in frequency characteristics of the video signal depending on the recording medium. be.

2. Description of the Related Art In recent years, video signal recording and reproducing devices have been developed using video tape recorders (
It has become popular in the consumer field, mainly in VTRs.
It has become a major pillar in the field of electronic equipment. Furthermore, there has been remarkable progress in recording media, and high-performance media are being commercialized one after another. An example of the conventional video signal recording and reproducing apparatus mentioned above will be described below with reference to one drawing. Figure 2 shows the difference in frequency characteristics due to the difference in magnetic tape in a VTR. A magnetic tape having characteristics 1 is generally called a normal tape. A magnetic tape having characteristics 2 is generally called a high-grade tape, and has finer magnetic particles than tape 1.

The magnetic surface is mirror-finished to improve response in high frequency ranges. It is generally well known that the frequency characteristics vary by 1 and 2 depending on the difference in magnetic tape. Recently, new magnetic materials have been actively developed, and the difference in frequency characteristics is widening. By the way, in the case of a VTR, it is common to record the video signal by FM modulating it, and according to the well-known VH3 standard, the sync chip = 3.4 (M
H2).

White peak = 4.4 (MHz).

In FIG. 2, the sync tip frequency is shown as 3, and the white peak frequency is shown as 4.

Generally, when demodulating an FM signal, it is known that a difference in frequency characteristics of the demodulated signal occurs due to a difference in response between a lower sideband and an upper sideband of the FM-modulated frequency displacement. The relationship is shown qualitatively below.

(Lower sideband>upper sideband) = The high frequency range of the reproduced video signal increases.

(Lower sideband + upper sideband) = The high frequency range of the reproduced video signal is lowered.

This is because the lower sideband contains much of the high-frequency spectrum of the video signal.

Therefore, the difference in frequency characteristics of the magnetic tapes in FIG. 2 is as shown in FIG. 3. If the high-frequency characteristics of the magnetic tape are insufficient, the high-frequency characteristics of the video signal will increase.In our experiments, the lower sideband (2M) h
) increases by 2dB.

The result is that the high frequency range (2MH2) of the video signal increases by 6 dB. This phenomenon is not unique to VTRs that use magnetic tape as a medium, but occurs in video recording and reproducing apparatuses that employ FM recording with a high degree of modulation. For example, the characteristics of a stylus-type or optical video disk are influenced by the resolution (frequency characteristics) of the disk that is the medium.

Problems to be Solved by the Invention However, in a video recording and reproducing device having the characteristics described above, the frequency characteristics of the video signal are affected by the frequency characteristics of the recording medium, so it is difficult to maintain stable frequency characteristics at all times. There was a problem in that it was not possible to obtain a reproduced video signal. In addition, in order to always obtain a stable video signal, it is necessary to record and reproduce the frequency characteristics of the video signal and to correct the deviation. In order to measure the frequency characteristics, a video sweep signal generator, an oscilloscope, etc. are required, which poses a cost problem.

In view of the above-mentioned problems, the present invention provides a video recording and reproducing apparatus that can obtain information for correcting the frequency characteristics of a video signal by recording and reproducing a simple test signal.

Means for Solving the Problems In order to solve the above problems, the video recording and reproducing apparatus of the present invention includes a test signal generator that generates a signal with an amplitude larger than the amplitude of the video signal to be FM modulated; There is a switch in front of the FM demodulator that switches between the video signal and the test signal, and a switch that reproduces the area where the test signal is recorded and outputs the amplitude (AM) in front of the FM demodulator.
) It is equipped with a M-detector for detecting a wave, and a signal processing means for using the M-detection output as information for correcting the frequency characteristics of a video signal.

Effect of the Invention With the above-described configuration, the present invention introduces a signal larger than the amplitude of the video signal, that is, a test signal, into the FM modulator via a switch, thereby generating a frequency displacement that sufficiently enters the lower sideband and upper sideband. The signal obtained by recording the signal on a recording medium and reproducing the recorded area is subjected to amplitude (AM) detection before FM demodulation. There is no output when the responses of the lower sideband and upper sideband of the recording medium are equal, and when the lower sideband becomes larger than the upper sideband, an output proportional to the lower sideband is obtained.

Therefore, based on the relationship between the responses of the lower sideband and upper sideband and the frequency characteristics of the video signal, the AM detection output can be used as information on the frequency characteristics of the video signal.

Embodiments Hereinafter, a video signal recording/reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a simplified block diagram of a VTR according to an embodiment of the present invention. In FIG. 1, a video signal is introduced into a 7M modulator 11, subjected to FM modulation, amplified by a recording amplifier 12, and recorded onto a magnetic tape 14 by a magnetic head 13. Further, during reproduction, the content recorded on the magnetic tape 14 is converted into an electric signal by the magnetic head 16, amplified by the head amplifier 16, FM demodulated by the 7M demodulator 17, and taken out as a video signal. This signal flow is the general signal processing of a VTR.

The present invention is realized by utilizing the signal flow inherent in the VTR. That is, the test signal generator 18 generates a signal with a larger amplitude than the video signal, and the switch 19 introduces it to the 7M demodulator 11 instead of the video signal, and the output of the head amplifier 16 is used for AM detection during playback. This configuration includes a M detector 2o that performs the following steps.

The operation of the video signal recording and reproducing apparatus configured as described above will be described below with reference to FIG. A signal having a larger amplitude than the video signal generated by the test signal generator 18 is introduced into the 7M demodulator 11 via the switch 19 and is converted to FM.
Modulated. At this time.

If it is a normal video signal, it is 3.4 to 4 in the case of VH8 standard.
．． a (MHz), but since the test signal has a large amplitude, it is modulated over a large frequency range. Therefore, the signal modulated by the test signal is recorded on the magnetic tape sufficiently including the lower sideband and the upper sideband. When the area where this signal was recorded is played back,
If a difference occurs between the lower sideband and the upper sideband, the reproduced signal will have a difference in amplitude. When this difference is detected by the AM detector 20.

It is possible to estimate the frequency characteristics of video signals.

From the relationship between the sidebands and the frequency characteristics of the video signal described above, when the detection output is large, the high frequency range of the video signal is enhanced, and when the detection output is small, the video signal becomes flat.

Although this embodiment has been described with respect to a VTR, the present invention can be similarly applied to other video signal recording and reproducing devices that use recording media other than magnetic tape and are based on high modulation degree FM modulation recording. .

Effects of the Invention As described above, according to the present invention, a video signal is switched to a test signal and recorded, and the frequency characteristics of the video signal can be determined from the M-detection output of the reproduced signal.

This is useful for always obtaining stable frequency characteristics of video signals, and it is easy to select the one with the optimal characteristics from among various magnetic materials or magnetic tapes with different processing methods. . In addition, the characteristics of magnetic tape are optimal and strong, ie.

It can be seen that when the M detection output is large, it is necessary to correct the frequency characteristics of the video signal.

Even if the frequency characteristics of the video signal are not corrected, the frequency characteristics after FM modulation can be corrected, or the electromagnetic conversion characteristics of the magnetic tape can be used to correct the recording current. In further development, it is also possible to implement a device that automatically performs the various corrections described above using the AM detection output.

The present invention provides superior effects in that it does not require special equipment compared to the conventional means of measuring and determining the frequency characteristics of a video signal using a video sweep signal generator and an oscilloscope. Furthermore, the test signals used in the above-mentioned embodiments of the present invention are as follows.

Since only the amplitude is desired for that purpose, there is no prescribed waveform and therefore it can be realized with an inexpensive configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a main part of an embodiment of the present invention, and FIG. 2 is a frequency characteristic diagram due to differences in magnetic tapes. FIG. 3 is a frequency characteristic diagram of a video signal due to differences in magnetic tape. 11...FM modulator, 13.15...
Magnetic head, 14...Magnetic tape, 17...
...FM demodulator. 18...Test signal generator, 19...Switcher, 2°...Music detector. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 oIZ34s6 M Dry (MHz) Magnetic tape Δ horse value', *@A raw Figure 3 o f 2 3 round thick soft (
100 Hz)

Claims (1)

[Claims] A test signal generator that generates a signal with an amplitude larger than the amplitude of the video signal input to the FM modulator, a switch that switches between the video signal and the test signal before the FM modulator, and a switch that records the test signal. A video signal characterized by having an AM detector that reproduces a region of a medium and performs amplitude detection before an FM demodulator, and a signal processing means that uses the AM detection output as information for correcting the frequency characteristics of the video signal. Recording and playback device.