JP3250021B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is so constructed that an audio FM signal from an audio head is deeply recorded on a magnetic tape, and subsequently a video FM signal from a video head is superimposed and recorded on the same track. And a magnetic recording and reproducing apparatus such as a high-fidelity VTR.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional Hi-Fi VTR of this kind.
2 shows a circuit configuration of a recording system in FIG. In the drawing, 1 is a luminance signal FM modulator, 2 is a color signal main converter, 3 is a luminance signal recording current adjustment variable attenuator, 4 is a color signal recording current adjustment variable attenuator, and 5 is a luminance signal. A color signal mixer, 6 is a constant current amplifier for a video head, 7 is an input bias resistor of the constant current amplifier 6, 8,
9 is a negative feedback resistor for setting a recording current, 10 and 11 are rotary transformers, and 12 and 13 are video heads for CH1 and CH2. Both video heads 12, 13 are mounted on a rotary head cylinder.

A video head 12 records a Hi-Fi audio FM signal to a deep layer on a magnetic tape by an audio head (not shown) and traces the same track thereafter.
According to (13), the video FM signal is recorded on the upper layer of the magnetic tape. At this time, the audio FM signal previously recorded in the upper layer of the magnetic tape is erased, and the audio FM signal remains only in the deep layer.

FIG. 6 shows an output level L of a recording / reproducing video FM signal by a video head in the case of multiplex recording as described above.
1 and recording / reproducing sound F by the sound head on the Hi-Fi side
FIG. 7 is a characteristic diagram showing an output level L2 of an M signal and an audio noise level L3 after FM demodulation (see the solid line for each) in relation to a luminance signal recording current. Playback sound FM
The C / N ratio (carrier-to-noise ratio) is shown in parentheses on the vertical axis for the signal output level L2. The recording current is set by adjusting the recording current adjusting variable attenuators 3 and 4 so that the C / N ratio of the Hi-Fi reproduction audio FM signal is maintained at a predetermined level. For example, F
In order to suppress the sound noise level L3 after M demodulated below -80dB, the recording current setting point shown in FIG. 6 P1
Variable attenuators for recording current adjustment
To adjust.

In this conventional Hi-Fi VTR,
The HiFi audio FM signal processing system and the video FM signal processing system are only related to the recording current adjustment by the recording current adjustment variable attenuators 3 and 4 only.
No feedback is applied between the two signal processing systems.

[0006]

However [0007], the feedback is not applied between the two signal processing systems, there are variations in the components such as the video heads 12 and 13 and the rotary transformer 10, 11 initially set 7 and if, in order to become erasing characteristics are different between the video head 13 of the video head 12 and CH2 of CH1, Fig. 8
As shown in (1), the output waveform of the Hi-Fi reproduction audio FM signal has a different C / N ratio between CH1 and CH2, and the reproduction audio may be degraded in quality. Although a pair of audio head hi-fi side output state by a head switching pulse shown in (c) of FIG. 8 is switched alternately reproduced audio F of CH2 For cases of (a) in FIG. 8
C / N ratio of the M signals has greatly reduced, shown in FIG. 8 (b)
In the case of (1), the C / N ratio of the reproduced audio FM signal of CH1 is greatly reduced.

Further, when recording / reproducing is repeated for a long period of time, time wear occurs on the video head, and the gap depth decreases. Then, as shown by a broken line in FIG. 6 , the output level characteristic of the recording / reproducing video FM signal by the video head shifts from L1 to L1 'on the lower side, and the output level of the recording / reproducing audio FM signal by the high-fidelity audio head. Is shifted from L2 to L2 ', and the sound noise level characteristic after FM demodulation is shifted from L3 to L3'. As a result, the output level of the hi-fi reproduced audio FM signal is reduced, resulting in a deterioration in the C / N ratio. In the initial state, the input bias resistor 7 in FIG. 7 is set so that the recording current set point P1 is weakly underbiased with respect to the output level characteristic L1 of the recording / reproducing video FM signal indicated by the solid line. However, the output level characteristic L1 'shown by the broken line
At the recording current set point P1, it is as if the setting was changed to a weak overbias, the amount of magnetic flux from the video head increases, and the high-fidelity sound previously recorded on the magnetic tape was increased. F
M signals will be erased more. As a result, as shown by L2 'and L3', the C / N ratio deteriorates, and at the same time, the noise level deteriorates and the S / N ratio (signal-to-noise ratio) also deteriorates. (A) of FIG. 9 shows an output waveform of the high fidelity of the reproduced sound FM signal in the initial state, (b) in FIG. 9 is a result of the shift to the strong side erase characteristics due to chronological wear of the head, the reproduced audio This shows a state where the C / N ratio of the output waveform of the FM signal has deteriorated.

The present invention has been made in view of the above circumstances, and suppresses a decrease in the output level of a high-fidelity reproduced audio FM signal with respect to timed wear of a video head, and also provides a C / C / D signal. An object of the present invention is to maintain an S / N ratio that is not different from the initial setting value by maintaining the N ratio at an appropriate value.

[0009]

A magnetic recording / reproducing apparatus according to the present invention deeply records an audio FM signal from an audio head on a magnetic tape, and subsequently superimposes a video FM signal from a video head on the same track. A magnetic recording / reproducing apparatus configured to perform surface recording on a single video FM signal capable of inputting a color composite video signal and supplying a constant current for recording a video FM signal to a video head; a constant current amplifier, and two peak detection rectifier circuit two audio heads to convert the outputs of the head amplifier for amplifying the reproduced audio FM signal picked up in the DC level, both pins
Mixer that mixes the DC level of the peak detection and rectification circuit
And the image F according to the DC level from the mixer.
Recording current control means for feedback-controlling the gain of the M signal recording constant current amplifier so that the level of the reproduced audio FM signal is maintained at a predetermined value.

[0010]

As a result of the timed wear of the video head due to long-term use, even if the amount of erasure of the previously recorded audio FM signal is increased and the output level of the reproduced audio FM signal by the audio head is reduced, the recording is performed. Since the gain of the video FM signal recording constant current amplifier by the current control means is feedback-controlled so that the level of the reproduced audio FM signal is maintained at a predetermined value, the C / N ratio of the reproduced audio FM signal can be appropriately maintained. Thus, the S / N ratio can be appropriately maintained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magnetic recording / reproducing apparatus (high fidelity VTR) according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a hi-fi VTR according to a first embodiment.
FIG. 3 is a block circuit diagram showing an electrical configuration of the embodiment. In the figure, 21 is a constant current amplifier for recording a video FM signal whose gain can be controlled, 22 is an input bias resistor of the constant current amplifier 21, 2
Reference numeral 3 denotes a bias voltage generator, 24 and 25 are recording current setting negative feedback resistors, 26 and 27 are rotary transformers of CH1 and CH2, 28 is a video head of CH1, and 29 is a video head of CH2. A color composite video signal from a Y / C processing circuit (not shown) is input to a non-inverting input terminal (+) of the video FM signal recording constant current amplifier 21. 30 is C
H1 hi-fi audio head, 31 is a hi-fi audio head for CH2, 32, 33 are rotary transformers, 3
Reference numerals 4 and 35 denote CH1 and CH2 hi-fi head amplifiers. The output terminals of the head amplifiers 34 and 35 are connected to a Hi-Fi FM demodulation circuit (not shown). The above circuit configuration is the same as that of the conventional example except that the gain of the video FM signal recording constant current amplifier 21 can be controlled.

The following elements are important circuit configurations of this embodiment. 41 and 42 are peak detection rectifier circuits (DC level converters) for converting the output level of the Hi-Fi reproduced audio FM signal output from the Hi-Fi head amplifiers 34 and 35 to DC by peak detection, and 43 is each peak detection rectifier circuit. A mixer for mixing and averaging the reproduced audio DC level signals of CH1 and CH2 output from 41 and 42, 44 is a microcomputer with an A / D converter, and 45 is a ROM attached to the microcomputer 44.
(Read only memory), 46 is a D / A converter.

The two peak detection and rectification circuits 41 and 42 and the mixer 43 are provided in the video head 28 of CH1.
And the erasing characteristic of the video head 29 of CH2 may be slightly different, and the DC level of the reproduced audio FM signal by the peak detection is different. Therefore, the reproduced audio FM signal of CH1 and the reproduced audio FM signal of CH2 are different. This is for obtaining an average value after individually converting to DC.

The reproduced audio DC level average signal obtained by the mixer 43 is sent to an input port of a microcomputer 44. The microcomputer 44 converts the reproduced audio DC level averaged signal into digital data by a built-in A / D converter. The ROM 45 previously stores the digital data value of the reproduced audio DC level averaged signal and the D / A converter 46 so as to optimize the recording current.
Is stored with a table in which data values to be transmitted are associated with each other. The conversion characteristic is linear as shown by the solid line in FIG. 2. However, when the interaction between the video heads 28 and 29 and the high-fidelity audio heads 30 and 31 is not linear, weighting is performed as shown by a two-dot chain line. It is necessary.

The conversion data corrected by the microcomputer 44 as described above is sent to a D / A converter 46, where it is converted into an analog gain control voltage signal, and the gain control voltage signal is converted to a video FM signal recording signal. It is input to the gain control terminal of the constant current amplifier 21. As a result, the constant current amplifier 21 adjusts the amplification factor for the input color composite video signal and adjusts the video heads 28 and 2.
Thus, a constant current, at which the recording current from No. 9 becomes an optimum value, is output.

For example, in the characteristic diagram of FIG. 6 , it is assumed that the recording current set point is set to P1 in order to suppress the audio noise level L3 after FM demodulation in the initial state to -80 dB or less. Then, it is assumed that the gap depth decreases due to the timed wear of the video heads 28 and 29, and the output levels of the Hi-Fi audio heads 30 and 31 decrease. That is, in FIG. 6 , it is assumed that the characteristics have shifted from the state indicated by the solid line to the state indicated by the broken line. Video heads 28, 29
Of the output level of the recorded / reproduced video FM signal due to L1
From L1 'to Hi-Fi audio head 30,
It is assumed that the characteristics of the output level of the recording / reproducing audio FM signal at 31 shift from L2 to L2 ', and the characteristics of the audio noise level after FM demodulation shift from L3 to L3'. At this time, the recording current setting point is automatically corrected downward from the point P1 to the point P2 by a feedback system from the high-fidelity audio heads 30 and 31 to the gain controllable video FM signal recording constant current amplifier 21.

If there is no feedback system as in the conventional example, the recording current setting point remains at the point P1, and the recording current setting point is changed with respect to the output level L1 'of the recording / reproducing video FM signal after the characteristic shift. When the point P1 is a solid line, the setting changes from a weak under-bias to a weak over-bias. Then, the amount of magnetic flux from the video heads 28 and 29 increases, so that the Hi-Fi audio heads 30 and 31 delete more Hi-Fi audio FM signals recorded on the magnetic tape ahead of time. The output level of the reproduced audio FM signal from the high-fidelity audio heads 30 and 31 decreases, and the C / N ratio deteriorates. At the fixed recording current set point P1, the audio noise level is N1 with respect to the audio noise level L3 after FM demodulation before the characteristic shift, but the audio noise level L3 'after FM demodulation after the characteristic shift. , The sound noise level changes to N2 and exceeds -80 dB, and the S / N ratio is clearly deteriorated.

However, according to the present embodiment, at the time of recording, the audio FM signal recorded in the deep layer by the hi-fi audio heads 30 and 31 is picked up, and the gain controllable video F is transmitted from the hi-fi audio heads 30 and 31.
Since the recording current set point is automatically corrected downward to the point P2 by the feedback system leading to the M signal recording constant current amplifier 21, the output level L1 'of the recording / reproducing video FM signal after the characteristic shift is also obtained. The recording current set point P2 can be kept in a weak under bias state, and the amount of erasure of the audio FM signal already recorded on the magnetic tape by the video heads 28 and 29 can be kept constant. That is, C of the reproduced audio FM signal
/ N ratio can be appropriately maintained. Also, for the audio noise level L3 'after FM demodulation after the characteristic shift, the recording current set point P2 becomes the audio noise level of N3, which is almost the same as the audio noise level N1 before the characteristic shift, The audio noise level can also be kept at an appropriate value of -80 dB or less. That is, the S / N ratio can be optimized.

The video heads 2 for CH1 and CH2
8 and 29 and the rotary transformers 26 and 27 have variations in characteristics.
Even if the erasing characteristics of the video head 28 of CH1 and the erasing characteristics of the video head 29 of CH2 for the audio FM signal recorded in advance by 0, 31 are different, CH1, C
Since the reproduced audio DC level signals of the H2 peak detection and rectification circuits 41 and 42 are averaged by the mixer 43,
Video FM for video heads 28, 29 of 1, CH2
A single constant current amplifier 21 as a constant current amplifier for signal recording
, The difference in the erasing characteristics can be covered, the problems shown in FIGS. 8A and 8B are eliminated, and the output waveform of the reproduced audio FM signal is output between CH1 and CH2. Can be kept almost the same. And
The adoption of a single shared constant current amplifier 21 and the accompanying D /
The circuit configuration can be simplified by unifying the A converter 46.

The microcomputer 44 and the D / A
The bus connecting the converter 46 may be serial or parallel. Further, the D / A converter 46 may be built in the microcomputer 44 and integrated.

FIG. 3 shows the positional relationship of the mounting of the video heads 28 and 29 for CH1 and CH2 and the audio heads 30 and 31 for hi-fi on the rotary head cylinder 20, and FIG. 4 shows the video heads 28 and 2 on the magnetic tape.
9 and the positional relationship between the Hi-Fi audio heads 30 and 31, and FIG. 5 shows a recording pattern of a video FM signal and an audio FM signal on a magnetic tape. These points are general and will not be described.

[0023]

As described above, according to the present invention, the recording current is automatically adjusted by the feedback control from the audio head to the video FM signal recording constant current amplifier. In contrast to this, it is possible to suppress a decrease in the output level of the reproduced audio FM signal
The C / N ratio can be properly maintained, and the S / N ratio can be appropriately maintained.

In addition, two peak detection rectifier circuits and both
A mixer that mixes the output of the
The difference in erase characteristics between the two video heads
Of the reproduced audio FM signals from the two audio heads due to
Be direct current level due to the peak detection are different, respectively
It can be averaged with a mixer after being individually converted to DC.
This increases the constant current for recording a single video FM signal.
Two sounds that cover the difference in erasure characteristics even when the width is shared
C / N ratio of output waveform of FM sound signal reproduced by voice head
Can be kept almost the same, and the circuit configuration can be simplified.
Can be simplified.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an electrical configuration of a magnetic recording / reproducing apparatus (high fidelity VTR) according to a first embodiment of the present invention.

FIG. 2 is a conversion characteristic diagram of a digital data value of a reproduced audio DC level averaged signal and a data value for gain control stored in a ROM in the first embodiment.

FIG. 3 is a plan view showing a positional relationship between a video head and a hi-fi audio head on a rotary head cylinder in the embodiment.

FIG. 4 is a diagram showing a positional relationship between a video head and a hi-fi audio head on a magnetic tape.

FIG. 5 shows a video FM signal and a sound FM on a magnetic tape.
FIG. 3 is a diagram showing a recording pattern with a signal.

FIG. 6 is a characteristic diagram showing an output level of a recording / reproducing video FM signal, an output level of a recording / reproducing audio FM signal, and an audio noise level after FM demodulation in relation to a luminance signal recording current.

FIG. 7 shows a conventional magnetic recording / reproducing apparatus (Hi-Fi V
FIG. 3 is a circuit configuration diagram of a recording system of TR).

FIG. 8 is a waveform diagram showing that a C / N ratio of an output waveform of a Hi-Fi reproduced audio signal becomes different between CH1 and CH2 in the conventional example.

FIG. 9 is a waveform diagram showing that the C / N ratio of the output waveform of the reproduced audio FM signal has deteriorated due to timed wear of the head in the conventional example.

[Explanation of symbols]

21: Constant current amplifier for recording video FM signal capable of gain control, 26, 27 ... Rotary transformer, 28 ... CH1
Video head, 29 ... CH2 video head, 30
… CH1 Hi-Fi audio head, 31… CH2
, Hi-Fi audio heads, 32, 33 ... rotary transformers, 34, 35 ... Hi-fi head amplifiers, 4
1, 42 ... peak detection rectifier circuit, 43 ... mixer,
44 microcomputer with A / D converter,
45 ROM, 46 D / A converter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/782-5/783 H04N 5/91-5/956 G11B 5/02-5/027

Claims (1)

(57) [Claims] 1. A sound F from a sound head on a magnetic tape.
A magnetic recording / reproducing apparatus configured to record an M signal in a deep layer and subsequently superimpose and record a video FM signal from a video head on the same track in a superimposed manner. each gain controllable single video FM signal recording constant-current amplifier for supplying a video FM signal recording constant-current, the output of the head amplifier two audio heads amplifies the reproduced audio FM signal picked up in DC level Two peak detection rectifier circuits for conversion,
Mixing the DC level of both peak detection and rectification circuits
And the gain of the video FM signal recording constant current amplifier according to the DC level from the mixer.
A magnetic recording / reproducing apparatus comprising: a recording current control unit that performs feedback control so that the level of the M signal is maintained at a predetermined value.