JPH06111211A - Envelope detecting circuit in magnetic recording/ reproducing apparatus - Google Patents

Abstract

PURPOSE:To obtain a detecting signal of a constant pulse width and obtain a noise-less image by making envelope outputs of two kinds of reproducing image signals constant and then comparing the outputs with a preset reference value. CONSTITUTION:FM signals taken by a pair of heads AH, BH are output as signals (a), (b) from preamplifiers 1A, 1B, and are turned to signals (c), (d) of the same amplitude by AGC circuits 2A, 2B. An output (e) of an envelope detector 3A is compared with the same reference level at comparators 5, 6 thereby to obtain outputs (g), (h). At the same time, outputs (i), (j) are obtained from an output (f) of a detector 3B through comparators 7, 8. Thereafter, a predetermined AND operation is carried out, to the outputs at gate circuits 11, 12 thereby to obtain detecting signals (k), (i) and (m), (n). In this constitution, a detecting signal of a constant pulse width is obtained irrespective of the amplitude of the reproducing FM signal, and therefore, it becomes possible to detect a good S/N part and obtain a noise-less image by detecting and selecting the reproducing FH signal with the use of the detecting signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an envelope detect circuit in a magnetic recording / reproducing apparatus capable of special reproduction of a two-track, two-program magnetic tape.

[0002]

2. Description of the Related Art As a conventional magnetic recording / reproducing apparatus, as disclosed in JP-A-59-104703, a pair of reverse azimuth first and second heads in the diameter direction of a rotating drum are provided. When the reverse azimuth third and fourth heads are provided, and the first and third heads and the second and fourth heads are reverse azimuth, respectively, and different programs are recorded on two adjacent tracks of the magnetic tape, One program is recorded by the first and second heads, and another program is recorded by the third and fourth heads.

When the magnetic tape recorded by the above-mentioned recording system is reproduced by a reproducing apparatus of two heads, another program is reproduced regardless of the trace pattern, and there is a disadvantage that compatibility is lost.

Therefore, the present applicant uses the first and second pair heads which are arranged in the diametrical direction of the rotary drum and which are composed of a pair of reverse azimuth magnetic heads so that two adjacent magnetic tapes can be formed. When recording two different programs on one track and performing special playback, first
And a discrimination signal for discriminating two different programs based on the envelope output of the reproduced video signal picked up by the second pair head, and a specific program signal is selected by the discrimination signal, and the selected specific signal is selected. The detected part of the program signal is written in the memory, the previous data is read out in the undetected part, and the detection position is shifted for each field by setting the playback speed to a non-integer multiple of the standard speed, and the signal for one screen is displayed. Suggested to get.

[0005]

However, when the discrimination signal for discriminating two different programs is generated based on the envelope output of the reproduction video signal as described above, the discrimination signal of the reproduction video signal depends on the level difference. If the pulse widths are different, noise cannot be always picked up because a good S / N ratio cannot be picked up.

[0006]

In order to solve the above problems, the first invention of the present application provides a level adjusting means for making the envelope outputs of two kinds of reproduced video signals constant, and an output from the level adjusting means. A comparison means for comparing with a predetermined reference value and a gate circuit for generating and outputting a signal for discriminating two programs based on the output from the comparison means are provided.

The second invention of the present application detects the amplitudes of the envelope outputs of the two types of reproduced video signals and outputs a reference value according to the detection results, and an amplitude detection means for the two types of reproduced video signals. A comparison means for comparing the envelope output with the reference value from the amplitude detection means, and a gate circuit for generating and outputting a signal for discriminating two programs based on the output from the comparison means are provided.

Further, according to the third invention of the present application, the center position detecting means for detecting the center position of the envelope output of the two types of reproduced video signals, and the center position detecting means for providing the discrimination signal of the pulse width corresponding to the search speed. A discrimination signal output means for outputting in synchronization with the detection result is provided.

[0009]

After the envelope outputs of the two types of reproduced video signals are made constant, they are compared with a predetermined reference value, or the envelope outputs of the two types of reproduced video signals are generated according to the detection result of the amplitude of the envelope output. By comparing with the reference value, and by outputting a pulse width determination signal corresponding to the search speed in synchronization with the center position of the envelope output, a constant pulse width determination is performed regardless of the envelope output level of the reproduced video signal. A signal can be obtained, and a noiseless image can be obtained by always picking up a good S / N ratio.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram of a head portion of a magnetic recording / reproducing apparatus used for implementing the present invention, FIG. 2 is a schematic diagram of a tape pattern of the same magnetic tape, and FIG. 3 is a relationship between a tape pattern and a trace by a magnetic head during special reproduction. It is a schematic diagram which shows.

This magnetic recording / reproducing apparatus includes a first pair head AH and a second pair head BH. First
Pair head AH is composed of a pair of reverse azimuth magnetic heads AH1 and AH2 which are paired in the diametrical direction of the rotary drum D, and the second pair head BH is composed of reverse pair azimuth magnetic heads BH1 and BH2 which are also paired. The magnetic heads are provided at the same height with respect to the axial direction of the rotary drum D, and the magnetic heads AH1, AH2, BH1, BH2 forming the first and second pair heads AH, BH are spaced 90 ° apart in the circumferential direction. It is arranged and its width is approximately equal to the width of the track.

The magnetic tape T is provided with recording tracks A1 and B1 of the same azimuth and recording tracks A2 and B2 of the opposite azimuth with a guard band GB interposed therebetween, and the magnetic head AH1 is provided on the track A1. Program A is recorded on the track B1, the program B is recorded on the track B1 by the magnetic head BH1, and the program A is recorded on the track A2 by the magnetic head AH2.
The program B is recorded on the magnetic recording medium 2 by the magnetic head BH2.

Therefore, during the special reproduction of the magnetic tape T, the reproduced video signal (hereinafter referred to as "reproduced FM signal") is traced from the same azimuth track A1, B1 to the reverse azimuth recording track A2, B2. Is output, the program A signal is reproduced first in the forward search, and the program B signal is reproduced first in the reverse search.

Next, FIG. 4 is a block diagram showing an embodiment of the first invention. The preamplifiers 1A and 1B for amplifying the reproduced FM signals picked up by the first and second pair heads AH and BH and the signals a and b output from the preamplifiers 1A and 1B are adjusted to the same level. Automatic gain control (hereinafter referred to as "AGC") circuits 2A and 2B as level adjusting means, envelope detectors 3A and 3B for detecting envelopes of output signals c and d of the AGC circuits 2A and 2B, and the envelopes. Output signals e of the detectors 3A and 3B,
Comparators 5 to 8 for comparing f with a predetermined reference value (reference level), and a gate circuit unit 9 for outputting discrimination signals k to n based on the output signals g to j of the comparators 5 to 8. Is equipped with.

The gate circuit section 9 outputs the output signal g of the comparator 5.
Gate circuit 1 that takes the AND of the output signal j of the comparator 8 and
1, a gate circuit 12 for ANDing the output signal g of the comparator 5 and the inverted signal of the output signal j of the comparator 8, and an AND of the output signal i of the comparator 7 and the output signal h of the comparator 6. And a gate circuit 14 for ANDing the output signal i of the comparator 7 and the inverted signal of the output signal h of the comparator 6.

The operation of this circuit will be described with reference to FIG. 5. The reproduced FM signal when searching the above-mentioned magnetic tape T is diagonally traced on the tape pattern at the search speed as shown in FIG. Therefore, since two tracks of the same azimuth follow two tracks of reverse azimuth, the first and second pair heads AH and BH
The signals a and b output from the preamplifiers 1A and 1B for amplifying the reproduced FM signals picked up by are in the form of discrete abacus.

Therefore, the levels of the signals a and b output from the preamplifiers 1A and 1B are adjusted by the AGC circuits 2A and 2B, and as shown in FIG. After being set to d, the envelopes are detected by the envelope detectors 3A and 3B, and the signals e and f are output.

The output signal e from the envelope detector 3A is compared with the reference levels by the comparators 5 and 6 to output the signals g and h as shown in FIG. 5, and the output signal f from the envelope detector 3B is output. , Comparator 7,
At 8 each is compared with the reference level and the signals i and j as shown in FIG. 5 are output.

Then, the comparator 5 is formed by the gate circuits 11 and 12.
By taking the AND signal g from the signal j and the signal j from the comparator 8 and a signal obtained by inverting the signal j, the discrimination signals k and l are output from the gate circuits 11 and 12,
Further, the gate circuits 13 and 14 obtain the AND signals of the signal i from the comparator 7 with the signal h from the comparator 6 and the inverted signal of the signal h, respectively.
Discrimination signals m and n are output from 4.

In this way, the discrimination signals k to n having a constant pulse width are obtained irrespective of the level of the reproduction FM signal. Therefore, by discriminating and selecting the reproduction FM signal by these discrimination signals, the S / N ratio is good. The part can be detected, and a noiseless image can be obtained. Then, by the A / B select switch 20 operated by the user,
Program A or B is selected through the / B separator 21 (program A is selected in FIG. 4), the sum of the selected signals from each head is A / D converted by the A / D converter 22, and this is The data is sequentially written in the memory 23. Here, the tape speed (search speed) is set to, for example, a non-integer multiple of the standard speed to shift the tracking, and the vertical scanning time of the reproduced FM signal picked up by each magnetic head is sequentially shifted to obtain a signal for one screen. When it becomes a signal for one screen, it is output through the D / A converter 24.

Next, FIG. 6 is a block diagram showing an embodiment of the second invention, and the parts after the A / B separator are the same as those in FIG. In this circuit, instead of the AGC circuits 2A and 2B for adjusting the levels of the signals a and b output from the preamplifiers 1A and 1B to the same level, the output signals e and f of the envelope detectors 3A and 3B are used. Of the envelope detectors 3A and 3B are provided with level detectors 15A and 15B as amplitude detecting means for detecting the level (amplitude) of the signal and generating and outputting a reference level according to the detection result. e and f are compared with the reference levels from the level detectors 15A and 15B.

The level detectors 15A and 15B are provided with the signals e from the envelope detectors 3A and 3B, respectively.
A signal of a level (for example, 80%) preset to the level of f is output as a reference level signal.

The signals of the respective parts in this circuit are as shown in FIG. 7. Even in this case, the reference level depends on the levels of the output signals e and f of the envelope detectors 3A and 3B, that is, the reproduced FM signal. Since the discrimination signals k to n having a constant pulse width can be obtained regardless of the level of the reproduction FM signal as in the above embodiment, the reproduction FM signal is discriminated and selected by these discrimination signals. By doing so, a portion having a good S / N ratio can be detected, and a noiseless image can be obtained.

Next, FIG. 8 is a block diagram showing an essential part of an embodiment of the third invention. In this circuit, waveform center detectors 16A and 16B that detect the center positions of the output signals e and f of the envelope detectors 3A and 3B, and a pulse width corresponding to the search speed based on the search speed information from the servo circuit 18 are used. And a discrimination pulse generator 17 for outputting the discrimination signals k to n in synchronization with the detection signals o and p from the waveform center detectors 16A and 16B.

In this circuit, the waveform center detector 1
As shown in FIG. 9, 6A and 16B output detection signals o and p at the center positions of the output signals e and f of the envelope detectors 3A and 3B, and the determination pulse generator 17 determines the pulse width according to the search speed. The signals k to n are output in synchronization with the detection signals o and p from the waveform center detectors 16A and 16B as shown in FIG.

Since the discrimination signal of the pulse width corresponding to the search speed is output at the center position of the reproduced FM signal in this way, a constant pulse width discrimination is made irrespective of the level of the reproduced FM signal as in the above embodiments. Since signals can be obtained, a reproduction FM signal can be discriminated and selected by these discrimination signals to detect a portion having a good S / N ratio, and a noiseless image can be obtained.

[0027]

As described above, according to the present invention,
After making the envelope outputs of the two types of reproduced video signals constant, they are compared with a predetermined reference value, or the envelope outputs of the two types of reproduced video signals are generated as reference values according to the detection result of the amplitude of this envelope output. Compared to
The discrimination signal is generated according to the comparison result, and the discrimination signal having the pulse width corresponding to the search speed is output in synchronization with the center position of the envelope output.
A discrimination signal having a constant pulse width can be obtained regardless of the level of the envelope output of the reproduced video signal, and a portion with a good S / N ratio can always be picked up to obtain a noiseless image.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a head portion of a magnetic recording / reproducing apparatus used for implementing the present invention.

FIG. 2 is a schematic diagram of a tape pattern of the magnetic tape.

FIG. 3 is a schematic diagram showing a relationship between a tape pattern and a trace by a magnetic head during special reproduction.

FIG. 4 is a block diagram showing an embodiment of the first invention.

FIG. 5 is a time chart showing signals at various parts of the circuit.

FIG. 6 is a block diagram showing an embodiment of the second invention.

FIG. 7 is a time chart showing signals at various parts of the circuit.

FIG. 8 is a block diagram showing an embodiment of the third invention.

FIG. 9 is a time chart showing signals at various parts of the circuit.

[Explanation of symbols]

2A, 2B ... AGC circuit (adjusting means), 3A, 3B ... Envelope detector, 5, 6, 7, 8 ... Comparator (comparing means), 9 ... Gate circuit section, 15A, 15B ... Level detecting section, 16A, 16B ... Waveform center detector (center position detecting means), 17 ... Discrimination pulse generator (discrimination pulse output circuit), AH ... First pair head, BH ... Second pair head, AH1, AH2, BH1, BH2 ... Magnetic head,
D ... Rotary drum.

Claims (3)

[Claims] 1. A first magnetic head arranged in a diametrical direction of a rotary drum and comprising a pair of magnetic heads of reverse azimuth.
And when performing special reproduction of a magnetic tape having two different programs recorded on two adjacent tracks by using the second pair head, based on the two types of reproduced video signals picked up by the first and second pair heads. In a magnetic recording / reproducing apparatus for discriminating two different programs, the magnetic recording / reproducing apparatus comprises level adjusting means for making constant envelope outputs of the two types of reproduced video signals,
Comparison means for comparing the output from the level adjusting means with a predetermined reference value, and a gate circuit section for generating and outputting a signal for discriminating two programs based on the output from the comparing means are provided. And an envelope detect circuit in a magnetic recording / reproducing apparatus. 2. A first magnetic head arranged in a diametrical direction of a rotary drum and comprising a pair of reverse azimuth magnetic heads.
And when performing special reproduction of a magnetic tape having two different programs recorded on two adjacent tracks by using the second pair head, based on the two types of reproduced video signals picked up by the first and second pair heads. In a magnetic recording / reproducing apparatus for discriminating two different programs, the magnetic recording / reproducing apparatus detects the amplitudes of envelope outputs of the two types of reproduced video signals and outputs a reference value according to the detection result. And comparing means for comparing the envelope outputs of the two types of reproduced video signals with a reference value from the amplitude detecting means, and a gate circuit for generating and outputting a signal for discriminating two programs based on the output from the comparing means. An envelope detect circuit in a magnetic recording / reproducing apparatus, wherein: 3. A first magnetic head which is arranged in a diametrical direction of a rotary drum and which is composed of a pair of reverse azimuth magnetic heads.
And when performing special reproduction of a magnetic tape having two different programs recorded on two adjacent tracks by using the second pair head, based on the two types of reproduced video signals picked up by the first and second pair heads. In a magnetic recording / reproducing apparatus for discriminating two different programs, the magnetic recording / reproducing apparatus has a center position detecting means for detecting a center position of envelope outputs of the two kinds of reproduced video signals and a pulse width corresponding to a search speed. An envelope detect circuit in a magnetic recording / reproducing apparatus, comprising: a discrimination pulse output means for outputting a discrimination pulse in synchronization with a detection result of the center position detecting means.