JPH0652941B2 - Rotating head type magnetic recording / reproducing device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an azimuth recording type rotary head type magnetic recording / reproducing apparatus widely used as a home VTR,
Particularly, the present invention relates to a rotary head type magnetic recording / reproducing apparatus suitable for performing variable speed reproduction such as high speed search reproduction, slow motion reproduction or still reproduction.

[Background of the Invention]

In a rotary head type magnetic recording / reproducing apparatus of an azimuth recording system, as is well known, for example, two rotary heads are made to have different azimuth angles from each other, and the magnetic tape is alternately helically scanned by these heads, and a video signal is recorded on the magnetic tape. The recording is sequentially performed on the recording tracks inclined at 1 field as a unit. Due to the difference in recording azimuth (recording magnetization direction) between the adjacent recording tracks, there is no stroke from the adjacent recording tracks at the time of reproduction. High-density recording can be performed without providing a guard band between storage tracks. However, in such an azimuth recording type rotary head type magnetic recording / reproducing apparatus, during the so-called variable speed reproduction in which the magnetic tape is run at a speed different from that at the time of recording or is stopped, that is, a plurality of rotary heads are used. The magnetic tape is reproduced and scanned with a rotary scanning locus that intersects with the recording track of the book, and its reproduction output is greatly reduced when the rotating head scans on a recording track having a recording azimuth that does not match its azimuth angle. However, such a decrease in reproduction output appears as a noise bar on the reproduction screen.

An example of variable speed reproduction in the rotary head type magnetic recording / reproducing apparatus of such an azimuth recording system will be described more specifically with reference to FIGS. FIG. 1 shows the relationship between the reproduction scanning locus by the rotary head and the recording track pattern when reproducing is performed by running the magnetic tape in the direction opposite to that at the time of recording for reproduction. Reference numeral 1 is a magnetic tape, and 2 and 3 are two rotary heads having different azimuth angles. The rotary heads 2 and 3 are mounted on a rotary drum (not shown) at an angular interval of 180 degrees as is well known. , Arrow a
Direction, the magnetic tape 1 is alternately rotated and scanned for each field of the video signal. 4, 5 are
While scanning the magnetic tape 1 in the direction of arrow b at a predetermined speed,
The recording tracks are formed by the alternate rotation scanning by the rotary heads 2 and 3, and the recording tracks 4 by the rotary head 2 and the recording tracks 5 by the rotary head 3 are sequentially and alternately formed. . 6,7
Shows a reproduction scanning locus by the rotary heads 2 and 3 when the magnetic tape 1 is run at a speed three times faster than that at the time of recording. These reproduction scanning loci are as shown in the figure. , The track pitch is three times the recording track pitch corresponding to the running speed of the magnetic tape 1, and the inclination angle thereof is significantly different from that of the recording tracks. It intersects diagonally. The hatched portions on the reproduction scanning loci 6 and 7 indicate the areas in which the rotary heads 2 and 3 reproduce and scan on the recording tracks recorded by the rotary heads 2 and 3 in this area. Since the azimuth angle of 3 coincides with the recording azimuth of the recording track, the rotary heads 2 and 3 can obtain a reproduction output that increases or decreases in accordance with the increase or decrease of the above area.

On the other hand, the reproduction scanning loci 6 and 7 without hatching
The rotary heads 2 and 3 are
This is an area for performing reproduction scanning on a recording track recorded by another rotary head. In this area, the reproduction output from the rotary heads 2 and 3 decreases to almost zero due to the difference in azimuth angle.

The reproduction output waveforms of such rotary heads 2 and 3 are shown in FIG. In the figure, (B) shows the reproduction output waveform of the rotary head 2, and (C) shows the reproduction output waveform of the rotary head 3.
The amplitudes of these reproduced output waveforms, that is, the envelopes of the reproduced FM video signals, increase and decrease corresponding to the crossing state between the reproduction scanning locus and the recording track, as is clear from the figure. 2 (A) shows a known head switching signal, and the FM video signal alternately reproduced from the rotary heads 2 and 3 by the switching signal is generated for each field, that is, the rotary heads 2 and 3 Each time the reproduction scanning loci 6 and 7 are scanned, they are alternately switched and taken out. The reproduced output waveforms of FIGS. 2 (B) and 2 (C) show reproduced FM video signals alternately extracted from the rotary heads 2 and 3 for each field in this way. These FM video signals are It is demodulated as one temporally continuous video signal and displayed on the television screen.

By the way, since the reproduced FM video signal includes an amplitude reduced portion where the amplitude becomes almost zero as described above, a great amount of demodulation noise is generated in the vicinity of the amplitude reduced portion during demodulation, and this is on the television screen. Appears as a noise bar. FIG. 3 shows a state where such a noise bar is generated. 8 is a television screen, 9 and 10 are FIG.
These are two noise bars corresponding to the reduced amplitude portion of the reproduced FM image signal shown in (B) and (C).

Conventionally, in order to prevent the occurrence of such a noise bar,
For example, as seen in Japanese Patent Laid-Open No. 49-9919, tracking control is performed by mechanically displacing the rotary head so that the tilt angle of the reproduction scanning locus during variable speed reproduction matches the tilt angle of the recording track. Although a method has been proposed, such a method has a drawback that its control configuration is complicated and expensive, and it is not practical.

[Object of the Invention]

An object of the present invention is to provide a rotary head type magnetic recording / reproducing apparatus capable of realizing variable-speed reproduction without noise by a relatively simple video signal processing circuit, excluding the above-mentioned drawbacks of the prior art.

[Outline of Invention]

In order to achieve this object, the present invention is arranged such that, for each field, the reproduced and demodulated image signal is temporarily stored in a memory according to a predetermined address and then sequentially read to obtain a reproduced image signal. The level of the reproduced FM video signal before demodulation is discriminated, the new video signal is written to the corresponding address of the memory and the stored content is rewritten only when the level is equal to or higher than a predetermined value, and the reproduction is performed. In a period in which the level of the FM video signal is not sufficient and noise occurs in the demodulated video signal, the noise-free video signal of the previous field is read without rewriting the stored contents of the memory. Characterize.

Example of Invention

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

FIG. 4 is a block diagram showing an embodiment of the present invention, in which 2 and 3 are two rotary heads having different azimuth angles shown in FIG. 1, 11 and 12 are amplifiers, 13 is a switch,
The switch 13 is supplied from the input terminal 14 of FIG.
Switching is controlled by the head switching signal (A). Reference numeral 15 is a demodulation circuit, 16 is a sync signal separation circuit, 17 is an analog-digital converter, 18 is a semiconductor memory, 1
Reference numeral 9 is a digital-analog converter, 20 is a memory control circuit, 21 is a level detector, 22 is a comparator, 23 is a reference voltage source of the comparator 22, and 24 is an output terminal of a reproduced video signal. Here, the FM video signals reproduced by the rotary heads 2 and 3 are amplified by the amplifiers 11 and 12, respectively, and are alternately switched by the switch 13 to form one continuous FM video signal. The FM video signal is demodulated by the demodulation circuit 15, and the demodulated video signal is converted into a digital video signal by the analog-digital converter 17. The analog-digital converter 17 has, for example, about 10 bits at 8 bits / word.
It is set to have a conversion speed of about 0 sec.

On the other hand, the output of the demodulation circuit 15 is also input to the sync signal separation circuit 16, and the sync signal separation circuit 16 separates and extracts the horizontal sync signal, the vertical sync signal and the color subcarrier signal from the demodulated video signal. By operating the memory control circuit 20 based on the signal, the analog-
The digital output of the digital converter 17 is repeatedly written for each one field and is written in a predetermined address of the semiconductor memory 18. The memory control circuit 20 also controls the reading of the memory 18, and the digital video signals written in the memory 18 are sequentially read in parallel with the writing, and the digital-analog converter 19 restores the original analog video signal. After being converted to, output from the output terminal 24. The memory control circuit 20 also controls the conversion operations of the analog-digital converter 17 and the digital-analog converter 19, and these conversion operations are synchronized with the writing and reading operations of the memory 18.

Further, the reproduced FM video signal obtained through the switch 13 is envelope-detected by the level detector 21 to detect the level thereof, and the comparator 22 detects the reference voltage source 2
Compared with 3. The level detector 21 and the comparator 22 are
It constitutes the level discrimination means of the reproduced FM video signal,
The level discrimination means supplies the discrimination output to the memory control circuit 20 only when the level of the reproduced FM video signal is equal to or higher than the predetermined level set by the reference voltage source 23.
Then, the memory control circuit 20 is configured to write a new digital video signal to the corresponding address of the semiconductor memory 18 and rewrite the stored contents only during the period when such a discrimination output is supplied. . Details of the configuration of such a memory control circuit 20 will be described later.

Next, description will be made of the operation in the case of performing variable speed reproduction of the recorded video signal by running the magnetic tape at a double speed in the direction opposite to that at the time of recording using the reproducing circuit according to the present embodiment. FIG. 5 shows the relationship between the recording track pattern on the magnetic tape corresponding to FIG. 1 and the reproduction scanning locus by the rotary head, and the portions corresponding to those in FIG. In the reproduction scanning loci 6 and 7, the hatched portions are areas where the rotary heads 2 and 3 reproduce on the recording tracks recorded by themselves, as described with reference to FIG. 1, and are not hatched. The intersections with the recording tracks 4 and 5 are areas where the rotary heads 2 and 3 reproduce and scan the tracks recorded by the other rotary heads.

FIG. 6 shows operation waveform diagrams when such variable speed reproduction is performed. (A) is a head switching signal, (B) and (C) are head switching signals (A) according to the rotary heads 2, 3 Is a reproduced FM video signal which is alternately switched and output every 1 field. The amplitudes of the reproduced FM video signals (B) and (C) are increased / decreased when the rotary heads 2 and 3 perform reproduction scanning of the hatched areas on the reproduction scanning loci 6 and 7, respectively, in relation to the recording azimuth. It increases or decreases in accordance with the above, and becomes almost zero at the time of reproducing and scanning the area other than the hatched area. (D) is the output waveform of the level detector 21 that is subjected to envelope detection after synthesizing the reproduced FM video signals (B) and (C). The level detection output waveform (D) is the reference of the reference voltage source 23 by the comparator 22. Voltage V _ref
And the discrimination output (E) that is at the high level in the period when the waveform (D) exceeds the reference voltage V _ref is obtained. The discrimination output (E)
Are supplied to the memory control circuit 20 as described above, and the digital video signal write operation to the memory 18 is performed only during the high level period.

Therefore, the stored contents of the digital video signal, which is repeatedly stored in the memory 18 at a predetermined address for each field, is sequentially rewritten to a new field video signal in the high level period of the discrimination output (E). In the low level period of the discrimination output (E), the video signal of the previous field remains without being rewritten. It should be noted here that the F reproduced by the rotary heads 2 and 3
As is clear from FIG. 6, the M video signals (B) and (C) are such that their amplitudes are opposite in increasing and decreasing phases.
This is because, in the present embodiment, the running speed of the magnetic tape is selected to be four times that during recording. Therefore, the phases of the discrimination output (E) corresponding to the increase / decrease phase of the amplitudes of the reproduced FM video signals (B) and (C) are also complementary to each other for each field. 1
By controlling the write operation of No. 8, in the memory 18, the noise portion generated corresponding to the decrease in the amplitude of the reproduced FM video signals (B) and (C) is the noise-free portion of the previous field. The interpolated digital video signal can be stored.

In general, when recording tracks are alternately formed by two rotary heads having different azimuth angles, if the running speed of the magnetic tape is set to an even multiple of the recording speed during variable speed reproduction,
The track pitch of the reproduction scanning locus is also an even multiple of the recording track pitch. Therefore, as shown in FIG. 5, the rotary heads 2 and 3 have different recording azimuths.
The order of alternately intersecting with and becomes the same, and the phase of increase and decrease of the reproduction output amplitude becomes opposite phase due to the difference in azimuth angle between these rotary heads. If the running speed of the magnetic tape is set to an odd multiple of the recording speed, the increase / decrease phase of the reproduction output amplitude from the rotary heads 2 and 3 becomes the same phase (see FIGS. 1 and 2).
Interpolative storage in the memory 18 as described above becomes impossible. Therefore, when using the rotary head type magnetic recording / reproducing apparatus according to the present embodiment, during variable speed reproduction (high speed reproduction), the running speed of the magnetic tape must be set to an even multiple of that during recording.

The digital video signal thus stored in the memory 18 is sequentially read out in parallel with the storage under the control of the memory control circuit 20 and converted into the original analog video signal by the digital-analog converter 19. It is converted and displayed on the Delevi screen. The television screen 8 is shown in FIG. This figure shows the projection state of the video signal at the field between t _{1 and} t _{2 in} FIG.
5 is an image portion by the reproduced FM video signal (B) in FIG. 6, and a projected portion 26 is a reproduced FM video signal (C) in FIG.
The image portion of the reproduced FM video signal
By interpolating the amplitude-decreased portion in (B), a variable speed reproduction screen without noise bars is obtained as a whole. It is needless to say that since the image signal has a strong field correlation, practically no trouble will occur even if the above interpolation for each field is performed.

Next, in the configuration of the embodiment shown in FIG. 4, a concrete configuration example of the sync signal separation circuit 16 and the memory control circuit 20 will be described with reference to FIG. In the figure, the parts other than the sync signal separation path 16 and the memory control circuit 20 surrounded by the dotted line are the fourth parts.
Since the configuration is the same as that of the figure, the same components are designated by the same reference numerals and the description thereof is omitted. Reference numeral 27 is a circuit that separates and extracts a color burst signal from the demodulated video signal output from the demodulation circuit 15 (see FIG. 4) and generates a color subcarrier signal that is phase-synchronized with the color burst signal. A quadruple multiplication circuit that multiplies the frequency f _{SC of the} subcarrier signal by 4, and the output of the circuit is supplied to the memory control circuit 20 as a clock signal. As the color subcarrier signal, a color subcarrier used in a reproduction color signal processing circuit of an ordinary magnetic recording / reproducing apparatus may be used, and in this case, the circuit 27 can be omitted. There is no end. 29 is a horizontal synchronizing signal separation circuit, 3
Reference numeral 0 denotes a vertical synchronizing signal separation circuit, which separates a horizontal synchronizing signal and a vertical synchronizing signal from the demodulated video signal input. Three
1 is a counter which receives the clock signal from the quadruple multiplication circuit 38 as a count input and which receives the horizontal synchronization signal from the horizontal synchronization signal separation circuit 29 as a reset input, and 32 counts the horizontal synchronization signal from the horizontal synchronization signal separation circuit 29. As input,
A counter that receives the vertical synchronizing signal from the vertical synchronizing signal separation circuit 30 as a reset input. The outputs of these counters 31 and 32 specify the write and read addresses of the memory 18. 33 is a write / read pulse generation circuit, and 4
Based on the clock signal from the multiplication circuit 28, the memory 18
A write pulse W and a read pulse R for are generated. An AND gate 34 is provided with the write pulse W at one input and the comparator 22 at the other input.
The write pulse W is supplied to the memory 18 only when the output from is input and the input from the comparator 22 is received.

Next, the operation of the circuit shown in FIG. 8 will be described with reference to the operation waveform charts shown in FIGS. 9 to 11. In FIGS. 9 to 11, signals corresponding to the signals in FIG. 8 are designated by the same reference numerals. The counter 32 includes the horizontal synchronization signal separation circuit 2
The horizontal synchronizing signal HS from 9 is sequentially counted, while the count value is reset every vertical period by the pulse VS 'synchronizing with the vertical synchronizing signal VS from the vertical synchronizing signal separation circuit 30. Therefore, the count value C ₁ is obtained from the counter 32. This count value C ₁ is 0 to 263 (actually 262.5H) at the time of standard reproduction of an NTSC video signal.
It becomes the count range of. The count value C ₁ is supplied to the semiconductor memory 18, and the addressing of the memory 18 in units of one horizontal period is repeated every vertical period. on the other hand,
The counter 31 sequentially counts the clock signal cp shown in FIG.
₂ is 1 by the pulse HS 'synchronized with the horizontal synchronizing signal HS (shown as a partially enlarged view in FIG. 10).
It is reset every horizontal cycle. The count range of the count value C ₂ of the counter 31 is 0 to about 910 (4 × f _SC / f _H , provided that
(f _SC is the color sub-carrier frequency, f _H is the horizontal sync frequency)
Becomes This count value C ₂ is supplied to the semiconductor memory 18 and designates a finer address within the designated address in units of one horizontal period designated by the counter 32.

Next, the semiconductor memory 1 based on such addressing
The operation of writing and reading the video signal to and from No. 8 will be described with reference to the operation waveform chart of FIG. The demodulated video signal from the demodulation circuit 15 (Fig. 4) is first input to the analog-digital conversion circuit 17, and the clock signal (Fig. 11 (A)).
After being sampled in synchronism with the falling edge of, the signal is converted into, for example, an 8-bit parallel digital signal. On the other hand, the write / read pulse generation circuit 33 outputs the write pulse W (shown in FIG. 11) which is delayed by a predetermined time from the falling edge of the clock signal.
(C)) and a read pulse R ((F) in FIG. 11) slightly delayed from the write pulse W are generated. The write pulse W is input to one input terminal of the AND gate 34, and is output only from the comparator 22 input to the other input terminal of the AND gate 34 (FIG. 11 (D)) at a high level. It is supplied to the semiconductor memory 18. A write pulse supplied from the AND gate 34 to the semiconductor memory 18 is shown in FIG. This write pulse is an address designation signal (Fig. 11 (Fig. 11 (Fig. 11)) in which the 8-bit parallel digital signal output from the analog-digital converter 17 is obtained during the high-level period based on the count values of the counters 31 and 32. Write to memory 18 according to B)). Here, the supply of the write pulse to the semiconductor memory 18 is stopped during the low level period of the output from the comparator 22 (FIG. 11 (D)), and the input signal is not written to the corresponding address. Since the stored signal before that remains, the semiconductor memory 18 has the low level period of the output from the comparator 22, that is, the rotary head 2, as described in FIGS. It is obvious that the digital video signal in which the noise generating part corresponding to the amplitude reduction period of the reproduced FM video signal from No. 3 is interpolated with the noise-free part of the previous field is stored.

The digital video signal stored in each address of the memory 18 is sequentially read out immediately after its storage by the read pulse R (FIG. 11 (F)) generated from the write / read pulse generation circuit 33, and an 8-bit parallel signal is read. The digital signal is input to the digital-analog converter 19 as a digital signal. The digital-analog converter 19 latches the input 8-bit parallel digital signal in synchronization with the rising edge of the clock signal (FIG. 11 (A)), and converts it into the original analog video signal. Output from the output terminal 24.

Needless to say, a variable-speed magnetic tape driving means is required for variable-speed reproduction of the recorded video signal using the reproduction signal processing circuit system as described above. Various driving means for such a magnetic tape are conceivable, one example of which is shown in FIG. In the figure, 1 is a magnetic tape, 35 is a capstan motor, 36 is a frequency generator (hereinafter referred to as FG) for detecting the rotation speed of the capstan motor 35, 37 is an amplifier,
38 is a frequency divider, 39 is a discriminator, 40 is a motor drive amplifier, 41 is an analog-digital converter, 4
Reference numeral 2 denotes a variable low resistance device connected to the power source E. When the capstan motor 35 is driven at standard speed, F
The frequency signal obtained from G36 is sufficiently amplified by the amplifier 37, and is input to the discriminator 39 of the next stage without being divided by the frequency divider 38.

The discriminator 39 discriminates the frequency of the input frequency signal to output a standard drive voltage, and the drive voltage is supplied to the capstan motor 35 via the drive amplifier 40. Next, during variable speed reproduction, operate the variable resistor 42,
A command voltage suitable for a desired gear ratio is applied to the analog-digital converter 41.

The analog-digital converter 41 converts the command voltage into a digital value and the frequency divider 38 proportional to the digital value.
Determine the division ratio of. Therefore, the discriminator 3
The frequency signal from the FG 36 is frequency-divided by a frequency division ratio proportional to the speed change ratio and is input to the disk 9.
Controls the capstan motor 35 by generating a control drive voltage so that the divided frequency is always the frequency at the standard speed. As a result, the capstan motor 35 rotates at a speed corresponding to the above gear ratio. Drive the magnetic tape 1.

In the embodiment shown in FIG. 4, as described above, in order to perform high-speed reproduction without noise, it is necessary to set the gear ratio of the magnetic tape 1 to an even number. In such a case, if the frequency division ratio specified value by the operation of the variable resistor 42 is N (N is a natural number), the frequency division ratio of the frequency divider 38 is set to 2N. Regardless of the operation, the speed change ratio of the magnetic tape is always an even number, which is convenient.

In the embodiment described above, the number of rotary heads having different azimuth angles is two, but the number of rotary heads is not necessarily limited to two, and for example, four (two with different azimuth angles are alternately provided. Obviously, the same can be done in the case of a set of rotary heads). It goes without saying that the present invention can be applied to not only high-speed reproduction but also low-speed reproduction (slow-motion reproduction), still reproduction, and the like.

〔The invention's effect〕

As described above, according to the present invention, during variable speed reproduction,
By using a memory for one field without using a mechanical rotary head tracking means, a noise portion generated during variable speed reproduction is stably interpolated by a video signal one field before, and pure electronically no noise variable speed reproduction. Since an image can be obtained, the mechanism is not complicated, the cost is low, and an excellent rotary head type magnetic recording / reproducing apparatus which eliminates the above-mentioned drawbacks of the prior art can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a reproduction scanning locus of a rotary head and a recording track pattern during high speed reproduction, and FIG. 2 is a waveform diagram showing a reproduction output of the rotary head during high speed reproduction shown in FIG. FIG. 3 is a diagram showing a television screen on which the reproduction output is displayed, FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG. 5 is a rotary head for performing high-speed reproduction according to the above embodiment. FIG. 6 is a diagram showing a relationship between a reproduction scanning locus and a recording track pattern, FIG. 6 is an operation waveform diagram at the time of high speed reproduction in the above embodiment, and FIG. FIG. 8 is a block diagram showing a more specific structure of the above embodiment, and FIG.
Fig. 10, Fig. 10 and Fig. 11 (A) to (F) are operation waveform diagrams,
FIG. 12 is a block diagram showing an example of magnetic tape driving means of the rotary head type magnetic recording / reproducing apparatus according to the present invention. 2, 3 ... Rotary head, 15 ... Demodulation circuit, 16 ... Synchronous signal separation circuit, 17 ... Analog-digital converter, 18 ... Semiconductor memory, 19 ... Digital-analog converter, 20 ... Memory Control circuit, 21 ... Level detector, 22 ... Comparator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayasu Ito, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Home Appliance Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-56-90684 (JP, A) JP JP 53-41921 (JP, A) JP 54-62719 (JP, A) JP 58-165487 (JP, A) JP 55-132178 (JP, A) JP 60-37890 (JP , A)

Claims (1)

[Claims] 1. A rotary head type magnetic recording / reproducing apparatus in which a magnetic tape is helically scanned by a plurality of rotary heads having different azimuth angles to record / reproduce a video signal for each field on each track on the magnetic tape. A means for continuously running the magnetic tape at a speed that is an even multiple of the recording speed during high-speed reproduction, and a video signal reproduced from the magnetic tape and demodulated, and a storage capacity for one field of the video signal And a detection means for detecting a noise generation period of a reproduced video signal from the magnetic tape due to the rotary head being displaced from a track on the magnetic tape during the high-speed reproduction, and a clock synchronized with the reproduced video signal. Based on the above, the write address is designated in order from the head address of the memory for each field period of the reproduced video signal. At the same time, each time the write address is specified, the address specified by this is specified as the read address, the writing and reading of the demodulated video signal to and from the memory are alternately performed, and the detection means A memory control circuit that prohibits writing to the memory and only performs reading during the noise generation period to be detected, and the noise generation period of the demodulated video signal during high-speed reproduction is already stored in the memory. The rotary head type magnetic recording / reproducing apparatus is characterized in that the rotary head type magnetic recording / reproducing apparatus replaces the reproduced video signal by the previous scanning with the rotary head.