JPH0771254B2 - Luminance signal reproduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Field B Outline of the Invention C Conventional Technology D Problems to be Solved by the Invention E Means for Solving Problems F Action G Example G-1 Configuration (Fig. 1) G-2 Operation (FIGS. 1 and 2) H Effect of the Invention A Field of Industrial Application The present invention relates to a magnetic tape recorded as frequency modulation signals on a plurality of inclined tracks in which luminance signals forming a video signal are arrayed. The present invention relates to a luminance signal reproducing circuit that obtains a reproduced luminance signal from a read signal of.

B Outline of the Invention The present invention relates to a circuit for reproducing a luminance signal from a read signal from a magnetic tape in which a luminance signal is recorded as a frequency modulation signal on a plurality of inclined tracks in which a luminance band is arrayed and formed in a magnetic tape. A frequency characteristic control unit is provided in the reproduction amplification unit connected to the output side of the magnetic head unit to obtain the read signal from the magnetic head unit, and when the magnetic head unit performs high-speed scanning for a plurality of inclined tracks formed on the magnetic tape, The detection time constant of the dropout detection unit connected to the output side of the amplification unit is set to be larger than that when the magnetic head unit normally scans a plurality of inclined tracks formed on the magnetic tape, and the drop The magnetic head forms the center frequency in the gain-frequency characteristic of the reproducing / amplifying unit on the magnetic tape according to the detection output obtained from the OUT detecting unit. Compared to the case where normal scanning is performed on a plurality of slanted tracks, the magnetic head is placed on the magnetic tape by controlling to change to the frequency side corresponding to the black level in the frequency-modulated luminance signal in the read signal. It is possible to effectively reduce a noise obstacle in a reproduced image obtained based on a reproduced luminance signal reproduced by performing high-speed scanning on a plurality of formed inclined tracks.

C Conventional Technology When a color video signal is recorded on a magnetic tape,
The luminance signal forming the color video signal and the carrier signal are separated, and the separated luminance signal is a frequency-modulated luminance signal frequency-modulated on the high frequency side (hereinafter referred to as FM luminance signal), and the carrier color signal is low. After being converted to a low-frequency carrier color signal (hereinafter referred to as low-frequency signal) that has been frequency-converted to the frequency side, both are mixed and supplied to the rotary magnetic head, and arranged inclining with respect to the running direction of the magnetic tape. The recording method of recording with the inclined track is widely adopted.

When such a recording method is adopted, when recording is performed under the relationship that the head width (track width) of the rotary magnetic head is smaller than the track pitch on the magnetic tape, a large number of magnetic tapes are recorded on the magnetic tape. The inclined tracks are formed in an array with a non-recording portion, that is, a guard band portion, between two adjacent ones of them, and the head width of the rotary magnetic head is equal to or larger than the track pitch on the magnetic tape. When recording is performed under the condition, a large number of inclined tracks are formed on the magnetic tape without a guard band portion. When a large number of slanted tracks are formed on the magnetic tape without a guard band portion, the recording density of the magnetic tape is increased to lengthen the recording time. On the other hand, crosstalk between adjacent tracks during reproduction. There is a disadvantage in terms of interference, and countermeasures against such crosstalk interference are required.

When a color video signal is reproduced from the magnetic tape on which the FM luminance signal and the low-pass color signal are recorded in this manner, a large number of inclined tracks arranged and formed on the magnetic tape are scanned by the rotary magnetic head. The FM brightness signal and the low-pass color signal recorded on each inclined track are read by the rotary magnetic head, and the brightness signal and the carrier color signal are reproduced based on the read signal obtained from the rotary magnetic head.
Then, in a mode in which the color video signal is reproduced from the magnetic tape, the rotary magnetic head sequentially scans a large number of inclined tracks arranged and formed on the magnetic tape. That is, not only the normal reproduction motor that performs normal scanning but also the high-speed reproduction mode in which the rotary magnetic head performs high-speed scanning in which a plurality of inclined tracks arrayed and formed on the magnetic tape are scanned over a plurality of them. Be taken. In the high-speed reproduction mode, the image content of the color image signal recorded on the magnetic tape is compressed by the reproduced image obtained based on the luminance signal and the reproduced color signal reproduced from the read signal obtained from the rotary magnetic head at that time. You can know it in time.

D. Problems to be Solved by the Invention When a color video signal is reproduced from a magnetic tape on which a large number of inclined tracks on which an FM luminance signal and a low-pass color signal are recorded are formed as described above, high-speed reproduction is performed. When the mode is adopted, for example, as shown in FIG. 3, a pair of rotating magnetic heads having different head azimuth angles and alternately abutting on the magnetic tape are applied to the magnetic tape. In the case where high-speed reproduction is performed on a tilted track T having an arrayed guard band portion g by a pair of rotary magnetic heads corresponding to the rotary magnetic heads at the time of recording, high speed is achieved by one rotary magnetic head. The scanning is the scanning locus as shown in FIG.
At the same time as Sa, the high speed scanning by the other rotary magnetic head is performed with the scanning locus Sb as shown in FIG. The azimuth angle of the rotary magnetic head at the time of recording corresponds to each of the rotary magnetic heads forming the scanning loci Sa and Sb, as shown by hatching in the scanning loci Sa and Sb, respectively. The FM luminance signal and the low-pass color signal recorded on the inclined track are sequentially read.

Therefore, in such a case, on the output side of the pair of rotary magnetic heads, the read signal Ra from one rotary magnetic head and the read signal Ra from the other rotary magnetic head, which has an envelope as shown in FIG. And the read signal Rb of are obtained alternately. Since each of the read signals Ra and Rb is such that the inclined track T arrayed and formed on the magnetic tape is accompanied by the guard band portion g, each rotary magnetic head generates an FM luminance signal and a low-pass color signal. A read signal missing portion Q is provided correspondingly during the period from the tilted track T for reading to the next tilted track T for reading the FM luminance signal and the low-pass color signal. Will be mixed with noise. When each of the read signals Ra and Rb passes through the regenerative amplifier, the noise in the read signal missing portion Q is also amplified to have a relatively large amplitude, and the read signals Ra and Rb obtained at the output side of the regenerative amplifier. The FM luminance signal separated from has a signal missing portion corresponding to each read signal missing portion Q, and the noise component on the frequency side corresponding to the white peak level in the FM luminance signal is compared to the signal missing portion. It will be mixed with a level on the frequency spectrum that is extremely large. Then, when the FM luminance signal mixed in the signal missing portion is demodulated in the demodulating portion with a level on the frequency spectrum in which the frequency side noise component corresponding to the white peak level in such an FM luminance signal is relatively large, In the demodulated output, that is, in the reproduced luminance signal, the noise mixed in the signal missing portion in the FM luminance signal is mixed as a large level noise, and the noise is a white peak. It may exceed the level.

Therefore, as shown in FIG. 3, in the case where high-speed scanning by the rotary magnetic head with the scanning loci Sa and Sb is performed on the inclined track T formed in an array on the magnetic tape along with the guard band portion g. In the high-speed reproduction mode as described above, for example, in the image reproduced on the screen of the color cathode ray tube display device based on the reproduction luminance signal and the reproduction color signal obtained at that time, the reproduction luminance signal is set as described above. Interference due to noise mixed in will appear with high brightness and become extremely noticeable.
Depending on the display device, such noise may cause the white peak level of the reproduction luminance signal to be clamped, and the image reproduced on the screen may become dark and depressed.

In view of such a point, the present invention demodulates an FM luminance signal obtained during a read signal from a magnetic tape in which a video signal including an FM luminance signal is recorded on a plurality of inclined tracks formed in an array with guard bands. When reproducing the luminance signal,
A magnetic head unit that obtains a read signal from the magnetic tape performs a high-speed scan on a plurality of inclined tracks formed on the magnetic tape, and a luminance signal reproduced based on the luminance signal is reproduced. It is an object of the present invention to provide a luminance signal reproducing circuit which can be effectively reduced.

E Means for Solving the Problems In order to achieve the above-mentioned object, the luminance signal reproducing circuit according to the present invention records a video signal including an FM luminance signal on a plurality of slanted tracks arranged with guard bands. The read amplification unit connected to the magnetic head unit to obtain the read signal from the read magnetic tape, and the demodulation unit and dropout for the FM luminance signal in the read signal from the magnetic head unit connected to the output side of the read amplification unit A compensator is included, which is connected to the output side of the luminance signal processing unit that obtains the reproduced luminance signal and the reproduction amplification unit, detects the dropout in the FM luminance signal in the read signal from the magnetic head unit, and outputs the detection. A dropout detector that controls the dropout compensator by
And a frequency characteristic control unit provided in the reproduction amplification unit. Then, when the dropout detection unit performs high-speed scanning on a plurality of inclined tracks formed on the magnetic tape by the magnetic head unit, the detection time constant for detecting dropout is the magnetic head unit formed on the magnetic tape. The frequency characteristic control unit controls the high-speed scanning of the plurality of inclined tracks formed on the magnetic tape by the frequency characteristic control unit. When performing the normal scanning of the center frequency in the gain frequency characteristic of the reproducing / amplifying unit according to the detection output obtained from the dropout detecting unit, the magnetic head unit normally scans a plurality of inclined tracks formed on the magnetic tape. FM in the read signal compared to
The control is performed to change to the frequency side corresponding to the black level in the luminance signal.

F action In the luminance signal reproducing circuit according to the present invention having such a structure, for a plurality of slant tracks on which a video signal including an FM luminance signal is recorded and arranged on a magnetic tape with guard bands. Under high-speed scanning by the magnetic head unit, the read signal obtained from the magnetic head unit is amplified by the reproduction amplification unit, and the FM luminance signal contained therein is supplied to the luminance signal processing unit. The signal missing part in the FM luminance signal caused by the guard band of is considered to have a large detection time constant compared to the case where the magnetic head part normally scans a plurality of inclined tracks formed on the magnetic tape. The detection output detected by the dropout detection unit and obtained from the dropout detection unit is supplied to the frequency characteristic control unit. Then, by the control in accordance with the detection output from the dropout detection unit by the frequency characteristic control unit, during the period when the signal missing portion in the FM luminance signal is being supplied to the luminance signal processing unit, the gain frequency of the reproduction amplification unit is The center frequency in the characteristic is changed to the frequency side corresponding to the black level in the FM luminance signal, as compared with the case where the magnetic head unit performs normal scanning on a plurality of inclined tracks formed on the magnetic tape.

This reduces the level on the frequency spectrum of the noise component on the frequency side corresponding to the white peak level in the FM luminance signal at the signal missing portion in the FM luminance signal that is amplified and extracted by the reproduction amplifier. Therefore, the FM luminance signal in which the level of the noise component has been reduced is demodulated in the demodulation unit in the luminance signal processing unit, and in the reproduction luminance signal obtained from the luminance signal processing unit, the FM luminance signal The noise mixed in the signal-missing part of 1 appears as noise of a relatively small level. Therefore, a noise obstacle in a reproduced image obtained based on such a reproduced luminance signal appears at a relatively low luminance and is less noticeable. That is, the noise disturbance on the reproduced image is reduced.

G. Embodiment G-1 Structure (FIG. 1) FIG. 1 shows an example of a luminance signal reproducing circuit according to the present invention. In this example, the luminance signal and the carrier color signal forming the color video signal are the FM luminance signal and the low-pass color signal, respectively, and the reproduced luminance signal is recorded from the magnetic tape TP recorded with the sequentially arranged inclined tracks. And a reproducing apparatus for obtaining reproduced carrier color signals. in this case,
The magnetic tape TP has a plurality of inclined tracks with a guard band portion, such as the inclined track T with a guard band portion g shown in FIG. 3, to which two FM luminance signals and low-pass color signals are supplied. The rotary magnetic heads are alternately arrayed and formed, and for example, an FM luminance signal and a low-pass color signal for one field period are recorded on each inclined track.

In FIG. 1, the rotary magnetic heads 1 and 2 are designed to alternately scan the magnetic tape TP on which a plurality of inclined tracks are arranged, and the FM recorded on the inclined tracks at each scan. Read the luminance and low-pass color signals. The output terminals of the rotary magnetic heads 1 and 2 are respectively
Select contact of switch 5 via regeneration amplifier circuits 3 and 4
It is connected to 5a and 5b. The switch 5 is responsive to the switching signal SW from the terminal 6 in synchronism with the period during which the rotary magnetic heads 1 and 2 contact-scan the magnetic tape TP, respectively.
And 5b are alternately connected, and as a result, amplified outputs of read signals by the rotary magnetic heads 1 and 2 are alternately derived to the movable contact 5c.

The movable contact 5c of the switch 5 is connected with a signal branching circuit 7 for separating the FM luminance signal and the low-pass color signal from the amplified output of the read signal by the rotary magnetic heads 1 and 2 obtained there. The carrier color signal reproduction circuit system 8 is connected to one output end of the branch circuit 7 from which the low-pass color signal is obtained, and the FM brightness signal is output to the other output end of the signal branch circuit 7 from which the FM brightness signal is obtained. Limiter 9
Are connected. The output terminal of the limiter 9 is connected to the input terminal of the demodulation unit 10 for the FM luminance signal from the signal branch circuit 7 that has passed through the limiter 9. Therefore, the FM luminance signal obtained from the magnetic tape TP by the rotary magnetic heads 1 and 2 and supplied to the demodulation unit 10 by the portion including the rotary magnetic heads 1 and 2, the switch 5, the signal branching circuit 7 and the limiter 9 described above. Therefore, a reproduction / amplification section is formed. This reproduction / amplification unit amplifies the FM luminance signal supplied to the demodulation unit 10 with a center frequency in a predetermined gain frequency characteristic.

The output terminal of the demodulation unit 10 is connected to the input terminal of the dropout compensation circuit 12 via the de-emphasis circuit 11. In addition, the output terminal of the limiter 9 has an FM supplied to the demodulation unit 10.
The input terminal of the dropout detection circuit 13 that detects the dropout portion in the luminance signal is also connected, and the output terminal of this dropout detection circuit 13 is the dropout compensation circuit 12
Is connected to the control end of the dropout compensation circuit 12
In, the demodulation output obtained from the demodulation unit 10, that is, the dropout unit in the reproduction luminance signal is compensated based on the detection output signal from the dropout detection circuit 13. The output terminal of the dropout compensation circuit 12 is connected to the luminance signal output terminal 15 via the filter circuit 14.

Further, in relation to the limiter 9 in the reproduction amplification section for the FM luminance signal obtained from the magnetic tape TP by the rotary magnetic heads 1 and 2 and supplied to the demodulation section 10, the gain frequency characteristic of this reproduction amplification section A frequency characteristic control unit 16 that changes the center frequency is provided. The output end of the AND circuit 17 is connected to the control end of the frequency characteristic control unit 16, and the pair of input ends of the AND circuit 17 are respectively the output end of the dropout detection circuit 13 and the rotary magnetic head. A high-speed reproduction mode signal 1 and 2 is obtained according to a high-speed reproduction mode in which high-speed scanning is performed by scanning over a plurality of inclined tracks arranged on the magnetic tape TP.
It is connected to terminal 18 which is supplied with FR. AND circuit 17
From the terminal 18, the high-speed reproduction mode signal FR is obtained from the terminal 18, and the control signal SC is obtained when the detection output signal from the dropout detection circuit 13 is obtained.
Changes the center frequency in the gain frequency characteristic of the reproduction amplification section according to the control signal SC from the AND circuit 17.

Further, in this example, the high speed reproduction mode signal FR from the terminal 18 is also supplied to the dropout detection circuit 13, and in the high speed reproduction mode, the detection time constant in the dropout detection circuit 13 is higher than that in the normal reproduction mode. It is designed to be large.

G-2 Operation (FIGS. 1 and 2) In an example of the luminance signal reproducing circuit according to the present invention constructed as described above, the rotary magnetic heads 1 and 2 are inclined tracks arranged on the magnetic tape TP. When scanning is performed, read signals alternately obtained from the rotary magnetic heads 1 and 2, respectively, are passed through the reproduction amplifier circuits 3 and 4, respectively, and then alternately taken out by the switch 5, and continuously read from the movable contact 5c of the switch 5. The read signal Rr is obtained and the signal branch circuit 7
Is supplied to. Then, the low-pass color signal Cc in the read signal Rr is derived from one output end of the signal branch circuit 7 and supplied to the carrier color signal reproducing circuit system 8, and the carrier color signal reproducing circuit system 8 reproduces the carrier color. The signal is obtained. On the other hand, from the other output end of the signal branching circuit 7, the FM luminance signal Yf in the read signal Rr is derived and supplied to the limiter 9, and the FM luminance signal Yf passed through the limiter 9 is supplied to the demodulation unit 10.

In the FM luminance signal Yf, the frequency corresponding to the tip of the sync signal is the first predetermined frequency fs (for example, 4.2 MHz), and the frequency corresponding to the white peak is higher than the first predetermined frequency fs. Is set to a predetermined frequency fp (for example, 5.4 MHz). The demodulation unit 10 has a frequency discrimination characteristic as shown in FIG. 2, for example, with respect to the FM luminance signal Yf, and is synchronized in correspondence with the first predetermined frequency fs of the FM luminance signal Yf. While taking the level Ls at the tip of the signal, white peaks corresponding to the second predetermined frequency fp
A reproduction luminance signal Y having a level Lp and a black level Lb slightly higher than the level Ls at the tip of the synchronizing signal is obtained at the output side thereof. Then, after the reproduced luminance signal Y is processed by the de-emphasis circuit 11 and the dropout compensation circuit 12, the luminance signal output terminal 15 is passed through the filter circuit 14.
Be derived to.

Regenerative amplifier circuits 3 and 4, switch 5, signal branch circuit 7
The reproducing amplifier for amplifying the FM luminance signal Yf supplied to the demodulator 10, which includes the limiter 9 and the limiter 9, is normally used for the rotary magnetic heads 1 and 2 with respect to a plurality of inclined tracks formed on the magnetic tape TP. In the normal reproduction mode in which scanning is performed, as shown in FIG. 2, the demodulation output level from the demodulation unit 10 is the white peak level Lp of the reproduction luminance signal Y.
The gain frequency characteristic has a center frequency of a frequency f ₀₁ higher than the second predetermined frequency fp in the FM luminance signal Yf, which is set to a higher level L ₁ .

Then, when the high speed reproduction mode is adopted, the high speed reproduction mode signal FR is supplied to the terminal 18. At this time, the read signals alternately obtained from the rotary magnetic heads 1 and 2 have read signal missing portions such as the read signals Ra and Rb including the read signal missing portions Q shown in FIG. 4, respectively. Will be accompanied. Therefore, the read signal Rr obtained from the movable contact 5c of the switch 5 has a read signal missing portion,
It is derived from the signal branching circuit 7 and goes through a limiter 9 to a demodulation section.
The FM luminance signal Yf supplied to 10 has a signal missing portion corresponding to the read signal missing portion, and the noise component is mixed in the signal missing portion with a relatively large level on the frequency spectrum. .

The signal missing portion included in the FM luminance signal Yf is detected by the dropout detection circuit 13 which is supplied with the high-speed reproduction mode signal FR from the terminal 18 and has a large detection time constant, and is detected by the dropout detection circuit 13. The detection output signal Do corresponding to the signal missing portion is obtained. This detection output signal Do is supplied to the control terminal of the dropout compensation circuit 12, and in the dropout compensation circuit 12, the drop appearing in the reproduced luminance signal Y obtained from the demodulation unit 10 at this time and passed through the de-emphasis circuit 11. Out compensation will be made.

Along with this, the detection output signal Do obtained from the dropout detection circuit 13 is supplied to one input terminal of the AND circuit 17, and at this time, the other input terminal of the AND circuit 17 is supplied with the high-speed reproduction mode signal from the terminal 18. Since FR is supplied, the control signal SC is obtained from the AND circuit 17 according to the detection output signal Do obtained from the dropout detection circuit 13, and this control signal SC is supplied to the frequency characteristic control unit 16. Then, the frequency characteristic control unit 16 supplies the FM luminance supplied to the demodulation unit 10 based on the control signal SC, which is formed by the portion including the rotary magnetic heads 1 and 2, the switch 5, the signal branch circuit 7 and the limiter 9. As shown in FIG. 2, the center frequency in the gain frequency characteristic of the reproduction amplification section for the signal Yf is calculated from the above-mentioned frequency f ₀₁ so that the demodulation output level from the demodulation section 10 is the white peak level Lp of the reproduction luminance vibration Y. FM luminance signal, which is assumed to be a level L ₂ between the black level Lb and the black level Lb
The frequency f ₀₂ is lowered to the frequency fb side corresponding to the black level in Yf.

As a result, the FM luminance signal at the signal missing portion in the FM luminance signal Yf that is amplified by the reproduction amplifier and supplied to the demodulator 10
Frequency fp corresponding to the white peak level in Yf
The level of the noise component on the side of the frequency spectrum is reduced. Therefore, in the reproduced luminance signal Y obtained at the output side of the demodulation unit 10 and led to the luminance signal output terminal 15, the FM luminance signal is included.
The noise mixed in the signal missing part in Yf appears as noise of a relatively small level. For this reason,
The noise obstacle in the reproduced image obtained based on the reproduced luminance signal Y appears at a relatively low luminance and becomes inconspicuous, and the noise obstacle on the reproduced image is reduced.

H Effect of the Invention As is clear from the above description, according to the luminance signal reproducing circuit of the present invention, the magnetic field is recorded from a magnetic tape recorded on a plurality of inclined tracks in which FM luminance signals are array-recorded with guard bands. FM in the read signal obtained through the head
When the reproduced luminance signal is obtained by demodulating the luminance signal, a high-speed reproduction mode is adopted in which the magnetic head unit performs high-speed scanning by scanning over a plurality of inclined tracks arranged and formed on the magnetic tape. Also, due to the noise mixed in the signal missing part in the FM luminance signal amplified by the reproduction amplifier and supplied to the demodulator, it appears in the reproduced luminance signal obtained at the output side of the demodulator. The noise can be of a reduced level.
Therefore, it is possible to make the noise disturbance in the reproduced image based on the reproduction luminance signal obtained under the high-speed reproduction mode inconspicuous as appearing at a relatively low luminance, and reduce the noise disturbance on the reproduced image. become.

[Brief description of drawings]

FIG. 1 is a block connection diagram showing an example of a luminance signal reproducing circuit according to the present invention, FIG. 2 is a characteristic diagram used for explaining the operation of the example shown in FIG. 1, and FIGS. FIG. 6 is a diagram which is used for describing a high speed reproduction mode in signal reproduction from a tape. In the figure, 1 and 2 are rotary magnetic heads, 3 and 4 are reproduction amplifier circuits, 9 is a limiter, 10 is a demodulator, 12 is a dropout compensation circuit, 13 is a dropout detection circuit, 15 is a luminance signal output terminal, 16 Is a frequency characteristic control unit.

Claims (1)

[Claims] 1. A reproducing / amplifying unit connected to a magnetic head unit for obtaining a read signal from a magnetic tape in which a video signal including a frequency-modulated luminance signal is recorded on a plurality of inclined tracks formed in an array with guard bands, A luminance signal processing section connected to the output side of the reproduction amplification section, comprising a demodulation section and a dropout compensation section for a frequency-modulated luminance signal in the read signal from the magnetic head section, and a luminance signal processing section for obtaining a reproduction luminance signal; Connected to the output side of the reproducing / amplifying unit to detect a dropout in a frequency-modulated luminance signal in a read signal from the magnetic head unit, and control the dropout compensating unit by a detection output obtained by the detection. When the magnetic head unit performs high-speed scanning of the plurality of inclined tracks, the detection of the dropout is performed. The magnetic head section is provided in the dropout detection section and the reproduction amplification section, which are larger in number than when the magnetic head section normally scans the plurality of tilted tracks. When performing high-speed scanning on a track, according to the detection output obtained from the dropout detection unit, the center frequency in the gain frequency characteristic of the reproduction amplification unit,
A frequency characteristic control unit for changing to a frequency side corresponding to a black level in the frequency-modulated luminance signal in the read signal, as compared with the case where the magnetic head unit performs normal scanning on the plurality of inclined tracks, Luminance signal reproduction circuit constructed.