JPH0748841B2 - Video signal recording method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal recording method in an apparatus for recording and reproducing a video signal using magnetic recording such as a video tape recorder.

2. Description of the Related Art When a signal containing a DC component such as a video signal is passed through a transmission system such as a magnetic tape that has a large amount of amplitude vibration, it is generally considered effective to frequency-modulate (FM) and transmit the signal. ing. In fact, it is well known that FM is mostly used for recording video signals in video tape recorders. When recording an FM signal on a magnetic tape, it is common to apply the FM signal directly to the magnetic head for recording. This is because even if the signal reproduced from the electromagnetic conversion system consisting of the tape and the head undergoes amplitude fluctuation and waveform distortion, the original video signal can be restored if the frequency can be detected because it is an FM signal. . (For example, "Recording and Reproduction of Video Signals" Shozo Nakagawa, Journal of the Television Society, Vol. 34, No. 12
Problems to be Solved by the Invention The method of recording a video signal using the conventional FM modulation as described above has been regarded as the most effective recording method in a VTR. However, VTR has recently been required to have high image quality, and in particular, as tape performance has dramatically improved, signal deterioration due to FM modulation recording has become a problem rather than tape noise.

Generally, the remanent magnetization characteristic of the electromagnetic conversion system has non-linearity that can be expressed by an odd function symmetric with respect to the origin, as shown in FIG. 4, and causes odd-order distortion such as third-order distortion. When an FM wave is applied to such an electromagnetic conversion system, the spectrum shown by the following equation is generated.

mΩ ± nω (1) Ω: angular frequency of carrier ω: angular frequency of modulated wave (signal) m, n: integer As a result, spurious signals represented by the following equation occur in the demodulated video signal.

(M ± 1) Ω + nω (2) Of these and the spurious, a component that enters the band of the video signal is generally called a moire, and fine mesh-like stripes appear on the screen to deteriorate the image quality. This moiré will become more of a problem when a wide band of VTR is required as in recent years. Moire in FM recording is caused by crosstalk between a video signal that is a modulated signal and an FM-generated signal, in addition to that caused by the non-linearity of the electromagnetic conversion system described above.
Some are due to the folding of the lower sideband spectrum, and some are generated by the mechanism of the demodulator, such as a pulse counting demodulator. Of these, there are circuit-related problems other than those caused by the non-linearity of the electromagnetic conversion system, and any component can be removed by the progress of circuit technology.
Therefore, if the moire due to the non-linearity of the electromagnetic conversion system can be reduced, the performance of FM modulation recording can be significantly improved and a high quality reproduced image can be obtained. However, there is a problem that the non-linearity of the remanent magnetization characteristic of the tape is essential and cannot be easily improved.

Means for Solving the Problems According to the present invention, when a video signal is stored by FM, a high frequency bias of several times to several tens of times the carrier frequency of frequency modulation is applied to a frequency modulated wave obtained by frequency modulating the video signal. Then, the magnetic recording head is supplied to record on the magnetic tape.

Action By applying a high frequency bias to the magnetic head to record a signal, the non-linearity of the residual magnetization characteristic of the tape is greatly improved. When FM waves are passed through this system, the beat component due to the non-linearity of the electromagnetic conversion system is greatly reduced. Therefore
If an appropriate FM modulation / demodulation circuit is selected, almost no moire will occur in the reproduced video signal, and VTR with extremely high image quality will be possible.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing frequency allocation of a rotary head type VTR which is an embodiment of the present invention. (A) is a frequency spectrum of the video signal 1 to be recorded, and has a band up to 5 MHz. (B) is a diagram showing frequency allocation of the recording signal, and the video signal has a frequency deviation from 6 MHz.
The frequency is modulated to 9MHz, and the lower side wave extends to about 1MHz. Although the upper side wave is limited in the recordable band, it can be reproduced by passing it through a limiter during demodulation. A high-frequency bias 3 is applied to the frequency-modulated signal 2 for recording. The high frequency bias frequency is selected to be several times to several tens of times the carrier frequency of the FM signal 2. High-frequency bias in magnetic recording is a technique that is commonly used in audio tape recorders, etc., and acts to significantly linearize the non-linear region of the remanent magnetization curve, which significantly improves the non-linear distortion of the electromagnetic conversion system. It is a method. However, in FM recording, the effect of distortion does not appear extremely, the effect is not clear at the bias frequency of several tens of MHz necessary for recording video signals, and in order to supply a high frequency bias via a rotary transformer. Since a high-frequency bias with a large amplitude is required and the circuit scale increases, the high-frequency bias is FM
It was never used for recording. This embodiment focuses on the effect of reducing the non-linear distortion even in a high frequency region where the high frequency bias is several tens of MHz, and intends to use it to improve Moire interference, which is an essential problem of FM recording of video signals. To do. As shown in FIG. 1 (b), by applying a high frequency bias 3 to the frequency modulated wave 2 of the video signal for recording, the characteristics of the electromagnetic conversion system directly come close to each other, and most of the beat components based on the carrier and signal frequencies are recorded. Does not occur. Therefore, the FM-demodulated reproduced video signal can realize a high-quality reproduced image containing no moire component.

FIG. 2 is a circuit diagram of a recording system main part circuit according to an embodiment of the present invention. In the figure, the video signal applied to the terminal 11 is FM-modulated by the FM modulator 4, amplified by the recording amplifier 5 and added to the synthesizer 6. On the other hand, a signal having a frequency of several tens of MHz is generated by the bias oscillator 7 as a signal for giving a high frequency bias magnetic field, amplified by the amplifier 8 and added to the synthesizer 6. The recording signal output from the synthesizer 6 is a high frequency bias superposed with an FM modulated wave, and the frequency allocation of the recording signal shown in FIG. 1B is realized. This recording signal is given to the rotary head 9 and recorded on the magnetic tape 10.

FIG. 3 is a rotary head type VTR which is another embodiment of the present invention.
It is a figure which shows the frequency allocation of. (A) is the frequency spectrum of the recorded input signal, in this case
The input is a composite color video signal 12, which is a so-called NTSC signal in which a carrier color signal indicated by a broken line is interleaved and multiplexed with a luminance signal. (B) is the frequency allocation of the recording signal in which the NTSC signal is FM-modulated as it is and a high frequency bias is applied.
The carrier color signal comes to the portion indicated by the broken line in the figure.

1 inch VTR that is often used as a broadcast VTR
There is a recording method called Direct FM. Generally, in the direct recording method in which a composite color video signal is directly recorded by FM, since the carrier color signal spectrum is considerably strong, a beat component with the carrier frequency of FM appears strongly, and it is easy to give moiré interference to the screen. To avoid this, the 1-inch VTR sets the FM carrier frequency very high. In other words, the band utilization efficiency is poor. On the other hand, if a high frequency bias is applied to the FM wave of the composite color video signal FM and bias recording is performed, the generation of beat components due to the non-linearity of the electromagnetic conversion system is suppressed, and a high-quality reproduced image with less moiré interference is obtained. be able to.
If the moire reduction effect of high frequency bias is used, the FM carrier frequency can be lowered to enable direct FM recording with improved band utilization efficiency.

EFFECTS OF THE INVENTION As is clear from the above description, according to the present invention, the video signal is
In the case of recording with a carrier frequency, it is configured to apply a high-frequency bias of several times to several tens of times the frequency-modulated carrier frequency to the frequency-modulated wave obtained by frequency-modulating the video signal and supply it to the magnetic recording head. The beat component generated between each frequency component of the input signal, that is, the moire interference,
Due to the high frequency bias effect, it can be made extremely small, and a high-quality reproduced image without moire interference can be obtained. Furthermore, since the beat component is small, it is not necessary to take special frequency allocation to avoid moire, and band utilization efficiency is improved. Further, since the high frequency bias is effective in improving the S / N of the electromagnetic conversion system, a reproduced image with a better S / N can be obtained. As described above, the FM recording method of the video signal using the high frequency bias is an excellent recording method that can significantly improve the image quality of the VTR.

[Brief description of drawings]

FIG. 1 is a frequency allocation diagram according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a recording system main part thereof, FIG. 3 is a frequency allocation diagram according to another embodiment of the present invention, and FIG. It is a characteristic view which shows the remanent magnetization characteristic of the electromagnetic conversion system used for the conventional VTR. 1 ... video signal, 2 ... frequency modulation signal, 3 ... high frequency bias, 4 ... FM modulator, 5 ... recording amplifier, 6 ...
Combiner, 7 ... Bias oscillator, 8 ... Amplifier, 9 ...
Rotating magnetic head, 10 ... magnetic tape, 13 ... frequency modulation signal, 14 ... high frequency bias.

Claims (2)

[Claims] 1. Recording on a magnetic tape by applying a high frequency bias of several times to several tens of times the carrier frequency of frequency modulation to a frequency modulated wave obtained by frequency modulating a video signal and supplying it to a magnetic recording head. A video signal recording method characterized by. 2. A video signal recording method according to claim 1, wherein the composite color video signal is frequency-modulated and a high frequency bias is applied to a frequency modulated wave for recording.