JPH06150538A - Magnetic recording / reproducing device - Google Patents

Abstract

(57) [Summary] [Configuration] The peak frequency of the characteristic can be controlled by varying the length of the delay line of the cosine equalizer.
Further, a feedback circuit and a lower sideband addition circuit are provided, and the feedback amount and the addition amount are controlled by the voltage obtained by envelope detection of the reproduction output. [Effect] By controlling the peak frequency, the feedback amount, and the lower sideband addition amount by the reproduction output, the resolution of the video signal can be improved when a high output tape is used. Further, it is possible to secure the inversion margin and the S / N in good balance in accordance with the reproduction output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus such as a VTR (video tape recorder), and more particularly to a VTR equalizer which can greatly contribute to an improvement in reproduced image quality.

[0002]

2. Description of the Related Art As a conventional technique of an equalizer used for amplitude equalization of an FM signal in a VTR, there is, for example, JP-A-2-18755. In the publication of this prior application, it is described that the low-frequency emphasis degree of the characteristic of the RF equalizer is controlled according to the amplitude of the reproduction signal, but the disclosed circuit is configured by a simple cosine equalizer. There is.

[0003]

By the way, in the prior art by the above-mentioned prior application, it is shown that the low-frequency emphasis degree of the equalizer characteristic is controlled according to the amplitude of the reproduction signal.
No consideration is given to securing the inversion margin while controlling the peak frequency of the equalizer characteristic according to the amplitude of the reproduction signal. Further, since the circuit disclosed in the embodiment of the above-mentioned prior application is composed of a simple cosine equalizer, the degree of freedom of the characteristic that can be controlled according to the amplitude of the reproduction signal is low, and the desired characteristic can be obtained. However, there is a problem that, for example, when a demagnetization tape having a very small output is reproduced, the reversal margin cannot be sufficiently secured, or the resolution improvement amount in a high output tape is small.

Therefore, the technical problem to be solved by the present invention is to solve the above-mentioned problems of the prior art,
The purpose is to improve the low degree of freedom of characteristics, which is a problem of the prior art. Another object of the present invention is to realize a variable peak frequency, a variable frequency band, and a variable lower sideband level, which are particularly required for an equalizer of a VTR, so that the equalizer can be more finely adjusted according to the amplitude of a reproduction signal. It is to optimize the characteristics.

[0005]

The length of a delay line used in an equalizer is made variable, and the peak frequency of the characteristic is controlled according to the amplitude of a reproduction signal.
Further, the cosine equalizer is provided with a feedback circuit and a lower sideband component adding circuit, and the coefficients of both circuits are controlled according to the amplitude of the reproduction signal. Further, the control sensitivity is changed according to each mode.

[0006]

By controlling the peak frequency of the equalizer characteristic according to the amplitude of the reproduction signal, it is possible to secure a sufficient reversal margin even when reproducing a demagnetized tape whose reproduction signal level is lower than the standard value. Further, by providing a feedback circuit in the cosine equalizer, the frequency band can be changed, and the optimum equalizer characteristic can be realized according to the magnetic tape. Further, by providing the lower sideband component adding circuit, it becomes possible to control only the lower sideband component, and it is possible to sufficiently improve the resolution in the high output tape.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the embodiments shown in FIGS. FIG. 1 is a circuit block diagram of a main part showing an embodiment in which a luminance signal FM equalizer of a VTR is constructed by using the present invention.

In FIG. 1, 1 is a magnetic tape, 2 is a magnetic recording / reproducing head, 3 is a preamplifier, and 4 is an HPF (High) having a characteristic of canceling the frequency characteristic of the magnetic recording / reproducing head.
passfilter), 5 is an envelope detection circuit for detecting the envelope level of the reproduced FM signal, 6 is a DC amplifier, 7
Is a variable resistor for gain adjustment for adjusting the control sensitivity of the sharpness Q of the frequency band of the equalizer characteristic, 8 is a variable resistor for gain adjustment for adjusting the control sensitivity of the lower sideband level of the equalizer characteristic, and 9 is Variable resistor for gain adjustment for adjusting the peak frequency control sensitivity of the equalizer characteristic, 10
Is a limiter circuit for limiting the upper limit value and the lower limit value of the control range of the peak frequency of the equalizer characteristic, 11 is a limiter circuit for limiting the upper limit value and the lower limit value of the control range of the lower sideband level of the equalizer characteristic, 12 Is a cosine equalizer (waveform equalization circuit). Reference numeral 13 is an input terminal of the cosine equalizer 12, 14 is an output terminal of the cosine equalizer 12, 15 is a control terminal for the peak frequency of the equalizer characteristic, 16 is a control terminal for the lower sideband level of the equalizer characteristic, and 17 is a frequency band of the equalizer characteristic. A sharp Q control terminal, 18 is an FM limiter for limiting the amplitude of the FM signal and extracting only phase information, 19 is an FM demodulator, and 20 is a VT including a de-emphasis circuit, a noise cancellation circuit, etc.
A video signal processing unit, which is a baseband signal processing circuit system of R, 21 is a video output terminal of the VTR. Further, inside the cosine equalizer 12, 22 and 27 are subtractors for analog signals, 25, 28 and 31 are adders for analog signals, and 23 and 24 are delay time T (f ₀ = 1 / (2
T); f ₀ is the peak frequency of the equalizer characteristic) delay line,
26 is a coefficient unit of 1/2, 30 is a coefficient unit having a value of K2, 32
Is a coefficient unit having a value of K1, and 29 is an LPF (Low pass filter) for extracting the lower sideband component of the FM signal.

Next, the signal flow of the circuit of FIG. 1 will be described. First, the reproduced FM signal obtained from the magnetic tape 1 and the magnetic recording / reproducing head 2 is amplified by the preamplifier 2 to a level at which signal processing is possible. This reproduced FM signal is divided into two, and first one is input to the HPF 4 having a characteristic of canceling the frequency characteristic of the magnetic recording / reproducing head 2, and the dependence of the reproduced FM signal amplitude on the FM carrier frequency is canceled. Next, a DC voltage proportional to the amplitude of this signal is taken out by the envelope detection circuit 5, and a system for controlling the peak frequency of the equalizer characteristic, a system for controlling the lower sideband level, and a control of the sharpness Q of the frequency band. It is divided into the system that performs. In the system for controlling the peak frequency of the equalizer characteristic, the DC voltage proportional to the FM signal amplitude is amplified by the DC amplifier 6, and the gain variation of the magnetic recording / reproducing head 2 and the preamplifier 3 is canceled by the gain adjusting variable resistor 9. After that, it is applied to the peak frequency control terminal 15 of the equalizer characteristic through the limiter circuit 10 for limiting the upper limit value and the lower limit value of the peak frequency control range. Similarly, in the system for controlling the lower sideband level, the DC amplifier 6, the gain adjusting variable resistor 8, the limiter circuit 11 for limiting the upper limit value and the lower limit value of the control range of the lower sideband level of the equalizer characteristic. A DC voltage is applied to the control terminal 16 of the lower sideband level of the equalizer characteristic via the. Further, in the system for controlling the sharpness Q of the frequency band, the sharpness Q of the frequency band of the equalizer characteristic is passed through the DC amplifier 6 and the gain adjusting variable resistor 7.
A DC voltage is applied to the control terminal 17 of the.

On the other hand, the reproduction FM obtained from the preamplifier 3
The signal is applied to the input terminal 13 of the cosine equalizer 12 after variations in the reproduction level of the FM signal are suppressed by the AGC circuit 33. Next, the cosine equalizer 12 cancels the amplitude reduction and the phase distortion in the high frequency region that occur during the magnetic recording / reproducing process, and takes out from the output terminal 14. The equalized FM signal from the output terminal 14 is
A video signal is obtained by the FM limiter 18 and the FM demodulation circuit 19, and signal processing such as de-emphasis and noise cancellation is performed by the video signal processing circuit 20, and then a reproduced video signal is output from the video output terminal 21.

Next, the operation inside the cosine equalizer 12 will be described. Cosine equalizer 12 of this embodiment
The circuit composed of the delay lines 23 and 24, the adder 25, the 1/2 coefficient unit 26, and the subtractor 27 is generally known as a cosine equalizer or transversal filter. The circuit of the cosine equalizer 12 in the present embodiment is the above-described cosine equalizer or transversal filter, a feedback circuit including a coefficient unit 32 and a subtractor 22 which are K1, and adders 28 and 31, and a coefficient unit 30 which is K2. , And a lower sideband component addition circuit composed of the LPF 29. The feedback circuit is provided in order to control the sharpness Q of the frequency band of the equalizer characteristic by changing the value of K1 of the coefficient unit 32, and the lower sideband component adding circuit is a coefficient unit. It is provided to make it possible to control the lower sideband level of the equalizer characteristic by changing the value of K2 of 30. In addition, the cosine equalizer 12 of this embodiment uses the delay lines 23 and 2 depending on the terminal voltage of the control terminal 15.
Since the length of 4 can be changed, the peak frequency of the equalizer characteristic can be controlled. Here, regarding the relationship between the terminal voltage and the equalizer characteristic, when the voltage of the control terminal 17 is increased, the value of K1 of the coefficient unit 32 of the feedback circuit is decreased, the feedback amount is decreased, and the sharpness Q of the frequency band of the equalizer characteristic is decreased.
The frequency band becomes wider. When the voltage at the control terminal 16 is increased, the value of K2 of the coefficient unit 30 in the lower sideband component addition circuit is increased, and the gain in the lower sideband region of the equalizer characteristic is increased. When the voltage of the control terminal 15 is increased, the lengths of the delay lines 23 and 24 are increased and the peak frequency of the equalizer characteristic is decreased. Further, in the case of the present embodiment, when the envelope level of the reproduced FM signal obtained from the preamplifier 3 is increased, the voltage of the control terminals 15, 16, 17 is increased in proportion thereto, so that the reproduced FM signal amplitude is increased. When playing a relatively large magnetic recording tape of
The voltage of the control terminals of 15, 16, 17 increases, the frequency band of the equalizer characteristic expands, the gain of the lower sideband region increases, and the peak frequency decreases.

In this embodiment, the method of controlling the three control terminals 15, 16 and 17 by using the detection signal of the envelope level of the reproduced FM signal has been described. However, it is also possible to apply two of the three to the terminals as a fixed voltage and to control only the remaining one terminal independently. Further, the limiter circuits 10 and 11 can be deleted because the DC amplifier 6 can have its characteristic. Further, the DC amplifier 6 is an envelope detection circuit 5
It is also possible to remove by adjusting the gain of. Further, the variable resistors 7, 8 and 9 for gain adjustment may be collectively provided between the envelope detection circuit 5 and the DC amplifier 6. Further, it may be provided between the envelope detection circuit 5 and the HPF 4.

Next, referring to FIG. 2, the characteristics of the HPF 4 shown in FIG. 1 will be described. Figure 2 shows VHS (N
It shows the frequency characteristic of the reproduced FM signal when applied to the TSC standard. In the standard, the video signal specifies that the sync tip is 3.4 MHz and the white peak is 4.4 MHz, and 3.7 M when the input video signal is a black signal.
Since it becomes Hz, 700 kHz is changed during this period. Therefore, the frequency characteristic 34 of the reproduced FM signal obtained from the magnetic tape 1, the magnetic recording / reproducing head 2, and the preamplifier 3
Since the amplitude of the reproduced FM signal changes depending on the video signal when the signal passes through, the envelope detection voltage also changes and the control of the equalizer characteristic becomes unstable. Therefore, by passing the filter (HPF4) having the HPF characteristic like the characteristic line 35, the flat characteristic like the characteristic line 36 can be realized, and the equalizer characteristic control can be stabilized.

Next, the method of controlling the above-mentioned three control terminals, which is a feature of this embodiment, will be described in detail. First, FIG. 3 shows a method of controlling the peak frequency of the equalizer characteristic. FIG. 3A shows the spectrum of the reproduced FM signal obtained from the magnetic tape 1, the magnetic recording / reproducing head 2 and the preamplifier 3, and FIG. 3B is an equalizer characteristic, FIG. 3C is a spectrum after equalization when the reproduced signal amplitude is higher than the standard value, and FIG. 3D is when the reproduced signal amplitude is lower than the standard value. It is the spectrum after conversion. Also,
37 is a carrier component of the FM signal, 38 is a first lower sideband component, 39 is a first upper sideband component, 40 is an equalizer characteristic when reproducing a magnetic recording tape having a relatively large reproduced FM signal amplitude, and 41 is a reproduction. It is an equalizer characteristic when a magnetic recording tape having a relatively small FM signal amplitude is reproduced. Further, in FIG. 3B, f ₀₁ and f ₀₂ are characteristic lines 4 respectively.
It is a peak frequency of 0,41.

In order to properly demodulate the reproduced FM signal obtained from the magnetic recording / reproducing system shown in FIG. 3A, a peak is generated at a frequency slightly higher than the carrier signal frequency of the FM signal as shown in FIG. 3B. Due to the equalizer characteristics that it has, it is necessary to correct the amplitude reduction in the high frequency range. Here, the setting of the peak frequency of the equalizer is very important. Generally, the peak frequency is set to the white peak of the FM signal (4.4 MH in VHS).
When it is set low so as to approach z), the S / N of the demodulated video signal is improved, but the margin for the inversion phenomenon of the carrier signal and the lower sideband signal is decreased. On the contrary, the peak frequency is the white clip of the FM signal (5.
4MHz), it is possible to obtain a margin for the inversion phenomenon, but S / of the demodulated video signal
N gets worse. On the other hand, the use of this embodiment can solve the conflicting problems described above. That is, first, when the amplitude of the reproduced signal is higher than the standard value, the FM
Since the C / N of the carrier is high and there is a margin for the inversion phenomenon, the peak frequency is lowered as f ₀₁ and peaking is performed around the carrier component 37 as shown in the spectrum of FIG. S / N of is given priority.
On the contrary, when the amplitude of the reproduced signal is lower than the standard value, the C / N of the FM carrier is low and the margin against the inversion phenomenon is small, so that the frequency near the white clip is peaked as shown in the spectrum of FIG. Then, the margin for the inversion phenomenon is prioritized.

Next, the minimum value f _{01 of} the peak frequency and the maximum value f ₀₂ of the peak frequency will be described. In the system of the embodiment of FIG. 1, the control range of the peak frequency of the equalizer characteristic is a minimum value f ₀₁ ≧ white peak frequency and a maximum value f _02.
≦ White clip frequency is required. The reason for this is that when the minimum value f ₀₁ <white peak frequency, the reproduction level near the white clip frequency is extremely lowered due to the frequency characteristics of the magnetic recording / reproducing system, and the inversion phenomenon easily occurs. is there. Further, when the maximum value f ₀₂ > white clip frequency, the frequency outside the band of the reproduction signal is peaked, and the S / N of the demodulated video signal is extremely deteriorated. Therefore, it is necessary to provide the system of FIG. 1 with the limiter circuit 10 having the characteristic of the envelope detection voltage-equalizer peak frequency as shown in FIG.

FIG. 5 shows a method of controlling the sharpness Q of the frequency band of the equalizer characteristic, which is the FM signal spectrum after equalization as in (c) and (d) of FIG. If the amplitude of the reproduced signal is higher than the standard value, there is sufficient margin for the above-mentioned inversion phenomenon.
As shown in FIG. 5A, the sharpness Q of the frequency band of the equalizer
Is lowered to widen the band to raise the first lower sideband component 38 with respect to the FM carrier 37 and improve the resolution of the demodulated video signal. When the amplitude of the reproduced signal is lower than the standard value, conversely, as shown in FIG. 5B, the sharpness Q of the frequency band of the equalizer is increased to narrow the band, and the first lower band with respect to the FM carrier 37. The wave component 38 is reduced to secure a margin for the inversion phenomenon.

6 and 7 show a method of controlling the lower sideband level of the equalizer characteristic. In FIG. 6, 42 is an equalizer characteristic when the amplitude of the reproduced signal is higher than the standard value, and 43 is an equalizer characteristic when the amplitude of the reproduced signal is lower than the standard value. In the equalizer 12 in the circuit of FIG. 1 of the present embodiment, the characteristics of 42 to 43 can be freely set by changing the voltage of the control terminal 16. At this time, the value of the coefficient unit K2 that realizes the characteristic of 43 is 0, which is equal to that of a general cosine equalizer. The value of the coefficient unit K2 that realizes the characteristic of 42 is 2.0 in this embodiment. FIG. 7 is a diagram of FIG.
This is the FM signal spectrum after equalization as in (b) of FIG. As for the operation, as in the case of FIG. 5, when the amplitude of the reproduction signal is higher than the standard value in (a) of FIG. The side gain is increased and the level of the first lower sideband component 38 with respect to the carrier is increased to improve the resolution of the demodulated video signal. When the amplitude of the reproduction signal is lower than the standard value, the frequency band of the equalizer is narrowed in FIG. 7B as in FIG. 5B, and the first lower sideband component with respect to the FM carrier 37. 38 is lowered to secure a margin for the inversion phenomenon.

FIG. 8 shows the relationship between the envelope detection voltage of the FM reproduction signal and the lower sideband component addition coefficient K2 in the control of the lower sideband level of the equalizer characteristic, where 44 is the standard tape speed. And 45 is a characteristic when the tape speed is 3 times. As shown in FIG. 8, the demagnetized normal tape, normal recording / reproducing normal tape, HG (high grade) tape, S-VHS (however, V
HS recording) Different envelope detection voltages are obtained in the order of the tape. In this embodiment, the normal tape on which normal recording / reproduction is performed is used as the standard output tape. Therefore, when the demagnetized normal tape is reproduced, the value of the lower sideband component addition coefficient K2 decreases, and (b) in FIG. ), The frequency band of the equalizer is narrowed, a margin for the inversion phenomenon is secured, and a stable video signal with less noise can be obtained. Further, in the HG (high grade) tape, the value of the coefficient K2 increases, the frequency band of the equalizer is widened as shown in FIG. 7A, and the level of the lower sideband component with respect to the carrier is increased to increase the resolution of the demodulated video signal. Is better than the normal tape used for normal recording and playback. Further, when an S-VHS (but VHS recording) tape is reproduced, a higher envelope detection voltage can be obtained due to its high output characteristic. However, as shown in FIG. 8, in the present embodiment, the value of the coefficient K2 is 2.0, for example. Is limited to. This is to prevent the value of the coefficient K2 from increasing too much and the level of the lower sideband component with respect to the carrier to rise too much, causing the frequency characteristics of the demodulated video signal to be out of balance and adversely affecting the image quality. The characteristic of limiting the value of the coefficient K2 may be realized by the limiter 11 as in the circuit of FIG. 1, but limitation by the power supply voltage of the DC amplifier circuit can also be used. Further, the characteristic 45 is set to be smaller than the change 44 in the change of the lower sideband component addition coefficient K2 with respect to the change of the envelope detection voltage of the FM reproduction signal. The reason for this is that when the value of the coefficient K2 is increased and the level of the lower sideband component with respect to the carrier is increased in the triple mode than in the standard mode, interference from adjacent tracks generated in the low frequency band of the FM signal is received. This is because it is easy. Further, if the control sensitivity of the triple mode is set lower than that of the standard mode in this way, it is possible to adjust the control sensitivity variation in the standard mode which requires relatively high frequency characteristic accuracy of the demodulated video signal. There is an advantage that it is not necessary to adjust the double mode.

FIG. 9 shows an example in which adjustment is made only in the standard mode. The circuit shown in FIG. 9 is basically the same as the circuit shown in FIG. 1, and the same parts are designated by the same reference numerals. Reference numeral 46 is an attenuator, and 47 is a standard and triple switch. In FIG. 9, a magnetic recording / reproducing head 2,
The variable resistor 8 for gain adjustment provided to absorb the variation of the preamplifier 3 is first adjusted in the standard mode. On the other hand, in the triple mode, the gain is reduced by the attenuator 46, so that even if there is a gain difference between the magnetic recording / reproducing head for the triple mode, the preamplifier and the magnetic recording / reproducing head for the standard mode, the variable equalizer. The control voltage applied to 12 has almost no effect. This can reduce the number of adjustment points. In FIG. 9, VH
Although the NTSC system of the S standard is described, it can be applied to SP and LP in the PAL system. Also NTSC / PA
It can be said that in the multi system corresponding to both the L system, the adjustment is made in the PAL mode and the NTSC is not made.

FIG. 10 shows the effect of improving the frequency characteristic of the demodulated video signal in the high output tape when this embodiment is used. Reference numeral 48 is a frequency characteristic when a normal tape which has been normally recorded and reproduced is reproduced, and 49 is H
A frequency characteristic when a high output tape represented by a G (high grade) tape is reproduced with the same equalizer characteristic as the characteristic of 48, and 50 is a high output tape reproducing the equalizer characteristic by using the embodiment of FIG. It is a frequency characteristic when it optimizes according to an envelope. Generally, a high output tape has excellent output characteristics in a short wavelength region, and a high frequency component is emphasized as an FM signal. For this reason, the carrier has a tendency to output a larger carrier than the normal tape in the level ratio of the lower sideband component to the carrier. Therefore, there arises a problem that the frequency characteristic is worse than that of the normal tape even though the tape is a high output tape like the characteristic of 49. . Therefore, in this embodiment,
Utilizing the fact that the reproduction output of a high-output tape is larger than that of a normal tape, the equalizer characteristic is changed, and the frequency characteristic is raised to a higher frequency band like the characteristic of 50, the resolution is improved, and the performance of the high-output tape is improved. You can make the most of it.

In the above description, the control of the FM signal processing system has been described, but a method of combining this with the video signal processing system to increase the effect on the reproduced image is also conceivable. For example, the output of the envelope detection circuit 5 in FIG. 1 may be further extracted and used in the noise canceller circuit or the aperture correction circuit in the video signal processing unit 20.

Furthermore, in the above embodiment, VHS
Although the method has been mainly described, it is needless to say that the present invention can be applied to the S-VHS method. In this case, in the S-VHS method for recording at a shorter wavelength than the VHS method, demagnetization of a magnetic tape, etc. Is likely to occur, the effect of the present invention can be expected to be further enhanced.

[0024]

As described above, according to the present invention, since the peak frequency of the equalizer characteristic can be changed according to the reproduction output, when the reproduction output is smaller than the standard value, a sufficient inversion margin can be obtained, and When the reproduction output is larger than the standard value, the S / N of the demodulated video signal can be prioritized, so that the inversion margin and the S / N which cannot be realized by the conventional technique can be secured in a good balance.

Further, by providing a feedback circuit and a lower sideband adding circuit in the cosine equalizer, it is possible to sufficiently secure the degree of freedom of the equalizer characteristic which cannot be realized by the prior art, for example, HG (high grade) tape. When using a high output tape such as, the resolution of the video signal can be greatly improved. In addition, in systems with different tape speeds such as standard and triple, control suitable for each mode can be realized, and good images with well-balanced resolution and noise can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part circuit of a VTR according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of characteristics of HPF in the circuit of FIG.

FIG. 3 is an explanatory diagram showing a method of controlling a peak frequency of an equalizer characteristic according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a control range of a peak frequency of an equalizer characteristic according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a method of controlling a bandwidth of an equalizer characteristic according to an exemplary embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an example of equalizer characteristics when the lower sideband level is controlled according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a method of controlling a lower sideband level of an equalizer characteristic according to an embodiment of the present invention.

FIG. 8 is an explanatory diagram showing an example of the relationship between the envelope detection voltage of the FM reproduction signal and the lower sideband component addition coefficient K2 in the control of the lower sideband level according to the first embodiment of the present invention.

FIG. 9 is a block diagram showing a main circuit in the case of adjusting only a standard mode according to another embodiment of the present invention.

FIG. 10 is an explanatory diagram showing an effect of improving frequency characteristics of a demodulated video signal in a high output tape according to an embodiment of the present invention.

[Explanation of Codes] 4 HPF having a characteristic of canceling the frequency characteristic of the magnetic recording / reproducing head 10 Limiter circuit for limiting the upper limit value and the lower limit value of the control range of the peak frequency of the equalizer characteristic 11 The lower sideband of the equalizer characteristic Limiter circuit for limiting the upper and lower limits of control range 12 Cosine equalizer (waveform equalizer circuit) 15 Peak frequency control terminal of equalizer characteristic 16 Lower side wave level control terminal of equalizer characteristic 17 Frequency band of equalizer characteristic Sharpness Q control terminal 30 coefficient unit that changes the amount of lower sideband addition 32 coefficient unit that changes the amount of feedback of the feedback circuit 35 characteristics of HPF 40 peak of the reproduced FM signal amplitude of the magnetic recording tape according to a relatively large state Equalizer characteristics when frequency is controlled. 41 The reproduction FM signal amplitude of the magnetic recording tape is the same. Characteristics when the peak frequency is controlled according to a relatively small state 42 Reproduction FM of magnetic recording tape Equalizer characteristics when the lower sideband level is controlled according to a relatively large amplitude of the magnetic recording tape 43 Reproduction FM of a magnetic recording tape Equalizer characteristics when the lower sideband level is controlled according to the condition that the signal amplitude is relatively small. 44 Characteristics showing the relationship between the envelope detection voltage and the lower sideband component addition coefficient K2 when the tape speed is standard. 45 The tape speed is 3 A characteristic showing the relationship between the envelope detection voltage and the lower sideband component addition coefficient K2 in the case of doubled. 46 Attenuator 47 Standard and triple switching switch 48 Frequency characteristic when playing back normal tape on which normal recording / playback is performed 49 HG ( High output tape represented by high grade) equalizer characteristics of 48 characteristics Frequency characteristic when the optimized according to equalizer characteristic to the envelope of the reproduced FM signal with the embodiment of FIG. 1 the frequency characteristic 50 high output tape when played back

Claims (9)

[Claims] 1. A magnetic recording / reproducing device comprising: a detection circuit for detecting the amplitude of a reproduction signal reproduced from a magnetic tape; and a waveform equalization circuit capable of controlling the peak point of the amplitude frequency characteristic by the output voltage of the detection circuit. In the device, when the amplitude of the reproduction signal is higher than the standard reproduction value, the peak point frequency of the amplitude frequency characteristic is lowered, and when the amplitude of the reproduction signal is lower than the standard reproduction value, the peak point of the amplitude frequency characteristic. A magnetic recording / reproducing apparatus having a high frequency. 2. The waveform equalization circuit according to claim 1, wherein the waveform equalization circuit is used for amplitude equalization of an FM signal so that the minimum value of the peak point frequency of the amplitude frequency characteristic does not become lower than the white peak frequency of the FM signal. A magnetic machine recording / reproducing apparatus provided with a limiting means and / or a limiting means so that the maximum value of the peak point frequency of the amplitude frequency characteristic does not become higher than the white clip frequency of the FM signal. 3. A detection circuit for detecting the amplitude of a reproduction signal reproduced from a magnetic tape, a first delay means and a second delay means connected in cascade, and an output of the first delay means for the first delay means. 1. A magnetic recording / reproducing apparatus having a feedback path for returning to the input of the delay means and having a waveform equalizing circuit capable of controlling the feedback coefficient of the feedback path by the output voltage of the detection circuit. When the amplitude is higher than the standard reproduction value, the feedback coefficient of the feedback path is reduced, and when the amplitude of the reproduction signal is lower than the standard reproduction value, the feedback coefficient of the feedback path is increased. Playback device. 4. A detection circuit for detecting the amplitude of a reproduction signal reproduced from a magnetic tape, a first delay means and a second delay means connected in cascade, an output of the first delay means and the first delay means. Means for adding the outputs of the second delay means, the output of the first delay means and the second
Of the delay means and means for adding the addition and subtraction outputs using the addition coefficient K2, and the waveform equalization circuit capable of controlling the addition coefficient K2 by the output voltage of the detection circuit. In the magnetic recording / reproducing apparatus provided with, the addition coefficient K2 is increased when the amplitude of the reproduction signal is higher than the standard reproduction value, and the addition coefficient K2 is decreased when the amplitude of the reproduction signal is lower than the standard reproduction value. A magnetic recording / reproducing apparatus characterized by: 5. The output terminal and waveform of a preamplifier according to claim 1, 3 or 4, wherein the waveform equalizing circuit is used for amplitude equalization of an FM signal to amplify the amplitude of the reproduced FM signal. A magnetic recording / reproducing apparatus characterized in that a filter having an amplitude-frequency characteristic whose amplitude-frequency characteristic cancels the amplitude-frequency characteristic of the magnetic recording / reproducing head is provided between the input terminals of the digitizing circuit. 6. The method according to claim 4, wherein the waveform equalization circuit is used for amplitude equalization of an FM signal, and the maximum value of the addition coefficient K2 is standardly reproduced only when the amplitude of the reproduction signal is higher than a standard reproduction value. When the amplitude of the reproduction signal is limited to twice the standard reproduction value, the addition coefficient K is proportional to the output voltage of the detection circuit without limitation.
2. A magnetic recording / reproducing apparatus characterized by making 2 small. 7. The frequency characteristic after FM demodulation according to claim 4, wherein the waveform equalization circuit is used for amplitude equalization of an FM signal and a magnetic tape having an amplitude of the reproduction signal equal to or less than a standard reproduction value is reproduced. In contrast, when the magnetic tape whose amplitude of the reproduction signal is a standard reproduction value or more is reproduced,
A magnetic recording / reproducing apparatus comprising means for controlling the addition coefficient K2 so that the frequency characteristic after M demodulation rises in the high frequency band of the video signal. 8. The method according to claim 4, wherein the waveform equalization circuit is used for amplitude equalization of an FM signal,
By providing a first reproduction mode in which the output from the magnetic tape is large and a second reproduction mode in which the output from the magnetic tape is small, the change of the addition coefficient K2 with respect to the change of the output voltage of the detection circuit is changed to the first. A magnetic recording / reproducing apparatus characterized in that it is smaller in the second reproducing mode than in the reproducing mode. 9. The change in the output voltage of the amplitude detection circuit according to the change in the amplitude of the reproduced FM signal in one of the first reproduction mode and the second reproduction mode according to claim 8, A magnetic recording / reproducing apparatus characterized in that no adjustment is made in the other one reproducing mode.