JPH04357792A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce the deterioration of a video signal due to cross talk by providing at least one means muting a reproduction luminance signal on the front stage of a keyed clamping circuit. CONSTITUTION:A switch 33 is provided, and the switch 33 is switched to the H side so as not to operate keyed clamping circuits 26 and 28 during the mute signal period from an input terminal 48, that is, the mute period due to a mute circuit 25, then the clamp pulse is not supplied to keyed clamp circuits 26 and 28. Further, a switch 22 is provided, and the switch 22 is held to the H side during the mute signal period from the input terminal 48 and held to the N side so as to prevent a DO signal from a dropout (DO) detection circuit 21 from being supplied to a DO compensation circuit 29, and the DO compensation circuit 29 is stopped. Thus, the generation of the synchronizing signals and clamp pulses can be stopped just after the mute is started.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to video signals and PCs, for example.
The present invention relates to a magnetic recording and reproducing apparatus that performs overlapping recording of M audio signals, and particularly to a magnetic recording and reproducing apparatus that is capable of after-recording (hereinafter referred to as dubbing).

0002

2. Description of the Related Art For example, in an 8 mm video standard VTR, as shown in FIG. , 104 are each equipped with a flying erase head 105, and tape guides 106 and 107 guide the magnetic tape 10.
1 is wound around a rotating cylinder 102 at an angle of about 216 degrees, and the two magnetic heads 103 and 104 scan the magnetic tape 101 at the same time. , video signals are alternately recorded in the remaining 180 degree area by magnetic heads 103 and 104, respectively. Such a recording method is called an overlap recording method.

FIG. 9 shows a recording pattern on a magnetic tape 101 formed by such overlap recording. The hatched 36 degree sections of the formed tracks 108, 109, 110, etc. are recording areas for PCM audio signals,
The 180 degree section shown in white is the recording area of the video signal. With such a tape format, it is possible to perform post-recording (hereinafter referred to as PCM post-recording) in which a PCM audio signal is recorded in a 36-degree section while reproducing a video signal from a 180-degree section.

During PCM post-recording, a large-amplitude recorded PCM audio signal crosstalks with a small-amplitude reproduced video signal in the rotary transformer, resulting in deterioration of the reproduced video signal. Therefore, mitigation measures such as JP-A-63-1
It is described in No. 87782.

[0005] In the 8mm video standard, the luminance signal is frequency modulated so that the frequency is higher on the white side.
A mode in which the carrier frequency of the frequency-modulated luminance signal (hereinafter referred to as FM luminance signal) is 4.2 MHz to 5.4 MHz (hereinafter referred to as low band mode), and a mode in which the carrier frequency of the FM luminance signal is set to 5. .7MHz~7.7MHz
There is a mode (hereinafter referred to as high band mode) in which In low band mode, the center frequency of the PCM audio signal is higher than the FM luminance signal. therefore,
When the crosstalked PCM audio signal is frequency demodulated, it becomes noise with a DC level higher than the 100% white level of the video signal. From this, the APL of the reproduced luminance signal
By detecting (Average Picture Level), it is possible to detect and clip the crosstalked PCM audio signal portion.

[0006]

However, the above-mentioned prior art relates to 8 mm video in low band mode and does not take into consideration 8 mm video in high band mode.

[0007] Furthermore, in the recording luminance signal processing circuit,
A key that clamps the tip of the synchronization signal before the frequency modulator
A key clamp circuit is provided, but even during playback, the key
Also, no consideration was given to processing the reproduced luminance signal using the dot clamp circuit.

An object of the present invention is to provide a magnetic recording and reproducing apparatus which can reduce crosstalk even in high band mode during PCM dubbing and which can use a keyed clamp circuit during reproduction to reduce deterioration of reproduced video signals. It is in.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a means for stopping the operation of a key clamp circuit during a period in which a PCM audio signal crosstalks during PCM post-recording, and At least one means for muting the reproduced luminance signal is provided upstream of the key clamp circuit.

0010

[Operation] During PCM post-recording, the video signal is muted because the video signal deteriorates due to the presence of noise during the period when the PCM audio signal crosstalks. Furthermore, during this period, the operation of the key clamp circuit is stopped to prevent the occurrence of sag due to clamping of the muted video signal.

Alternatively, by stopping the operation of the dropout compensation circuit during the above-mentioned period, the synchronization separation circuit at the subsequent stage of the dropout compensation circuit does not output a synchronization signal. Therefore, since the clamp pulse generation circuit that generates clamp pulses from the synchronization signal does not output clamp pulses, the keyed clamp circuit described above does not operate, and the occurrence of sag can be similarly prevented.

0012

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a magnetic recording and reproducing apparatus according to the present invention, in which 1 is a magnetic tape, 2 and 3 are magnetic heads, 4 is a rotary transformer, 5 is a recording and reproducing amplifier, and 6 is a control. Signal generation circuit, 7 is an output terminal for a reproduced PCM audio signal, 8 is an input terminal for a recorded video signal, 9 is an adder, 1
0 is a pilot signal input terminal, 11 is a recording PCM audio signal processing circuit, 12 is an audio signal input terminal, 13 is a mode signal input terminal, 14 is a head switching signal input terminal,
15 is an input terminal for an after-recording mode signal, 16 is a mute circuit, 17 is a peaking circuit, 18 is an FM/AGC (automatic gain control circuit) circuit, 19 is a limiter, 20 is a frequency demodulation circuit, and 21 is a DO (dropout) detection circuit, 2
2 is a switch, 23 is a de-emphasis circuit, 24 is L
PF (low pass filter), 25 is a mute circuit, 26
27 is a keyed clamp circuit, 27 is a nonlinear de-emphasis circuit, 28 is a keyed clamp circuit, 29 is a DO compensation circuit, 30 is a 1H (H is one horizontal scanning period) delay line, 31 is a noise cancellation circuit, and 32 is a synchronous separation circuit. 33 is a switch, 34 is a clamp pulse generation circuit, 35 is a reproduced chroma signal processing circuit, 36 is an LPF, 37 is an ACC (automatic chroma level control) circuit, 38 is a frequency conversion circuit, 39 is a BPF (band pass filter) , 40 is a comb filter, 41 is a burst de-emphasis/chroma de-emphasis circuit, 42 is a color killer switch, 43 is a mute circuit, 44 is an adder, 45 is a BPF, and 46 is a reproduction F.
M audio signal processing circuit, 47 is an input terminal for a PCM gate signal, 48 is an input terminal for a mute signal, 49 is an output terminal for an FM audio signal, 50 is an output terminal for a chroma signal, and 51 is an input terminal for a composite video signal. The output terminal 52 is a luminance signal output terminal.

Next, the operation of this embodiment will be explained.

In the case of normal recording, a pilot signal for tracking control during playback from input terminal 8 and F
The video signal on which the M audio signals are multiplexed is sent to the recording/playback amplifier 5.
After being amplified, the signal is supplied to the magnetic heads 2 and 3 via the rotary transformer 4 and recorded on the magnetic tape 1. This video signal here is a multiplex of an FM luminance signal and a low frequency converted chroma signal, and further multiplexed with an FM audio signal. The recording/reproducing amplifier 5 is controlled by the control signal generating circuit 6 in a recording mode in response to a mode signal from an input terminal 13 and in response to a head switching signal SW(+) from an input terminal 14.

In the case of normal playback, the recording/playback amplifier 5
is placed in the reproduction mode by the mode signal from the input terminal 13, and is controlled in accordance with the head switching signal SW(+) from the input terminal 14. At this time, the mute signal is not supplied from the input terminal 48, the PCM gate signal is not supplied from the input terminal 47, and the post-recording mode signal AF is not supplied from the input terminal 15.
allows the input signal to pass through without performing a mute operation, and switches 22 and 33 are closed to the L side.

In such a state, the video signal reproduced from the magnetic tape 1 by the magnetic heads 2 and 3 passes through the rotary transformer 4, is amplified by the recording/reproducing amplifier 5, passes through the mute circuit 16, and is output to the FM The luminance signal is equalized by a peaking circuit 17, processed by an FM/AGC circuit 18 and a limiter 19, and then supplied to an FM demodulation circuit 20 to obtain a demodulated luminance signal. This luminance signal is processed by a de-emphasis circuit 23 and an LPF 24, passes through a mute circuit 25, and further passes through a keyed clamp circuit 26, a non-linear de-emphasis circuit 27, and a keyed clamp circuit 2.
8 and is supplied to the N side of the DO compensation circuit 29, which is a switch.

On the other hand, the output FM luminance signal of the FM/AGC circuit 18 is supplied to the DO detection circuit 11 to detect dropout, and the detection signal is sent to the DO detection circuit 11 via the switch 22.
It is used to control the compensation circuit 29.

The DO compensation circuit 29 is normally closed to the N side, and the output luminance signal of the keyed clamp circuit 28 passes through the DO compensation circuit 29 and is supplied to the noise canceling circuit 31 and the sync separation circuit 32. 1H delay circuit 30
The signal is delayed and supplied to the DO side of the DO compensation circuit 29. When the DO detection circuit 21 detects dropout, the DO compensation circuit 29 closes to the DO side during the signal period (dropout period) of the detection signal. Thereby, the dropout period of the output luminance signal of the keyed clamp circuit 28 is compensated by the luminance signal 1H before from the 1H delay circuit 30, and dropout is compensated.

The synchronization separation circuit 32 separates the synchronization signal from the luminance signal from the DO compensation circuit 29. This synchronization signal is used in a well-known manner, but is also supplied to a clamp pulse generation circuit 34, which generates a clamp pulse from its leading edge. This clamp pulse is supplied to the keyed clamp circuits 26 and 28 via the switch 33, and clamps the leading end of the synchronization signal of the luminance signal to a predetermined potential.

The luminance signal processed by the noise canceling circuit 31 is output from the output terminal 52 and is also supplied to the adding circuit 44 .

The output video signal of the mute circuit 16 is an AC
The signal is supplied to a well-known reproduced chroma signal processing circuit 35 consisting of a C circuit 37, a frequency conversion circuit 38, etc., and a BPF 45. The BPF 45 separates the FM audio signal added to the video signal, and this FM audio signal undergoes processing such as demodulation in the reproduction FM audio signal processing circuit 46 and is output from the output terminal 49. The reproduced chroma signal processing circuit 35 separates the chroma signal from the reproduced video signal and performs processing such as frequency conversion and removal of crosstalk from adjacent tracks, and this chroma signal is sent to the color killer switch 42 and the mute circuit 4.
3 to an adder 44 and an output terminal 50. The adder circuit 44 adds the luminance signal and the chroma signal,
It is outputted from the output terminal 51 as a composite video signal.

Next, the operation during PCM post-recording will be explained. In this case, the recording/reproducing amplifier 5 enters the reproduction mode for the video signal in response to the mode signal from the input terminal 13, and receives the post-recording mode signal A from the input terminal 15.
F causes the PCM audio signal to enter the period recording mode of the PCM gate signal from the input terminal 47. This P
The CM gate signal represents the period during which the magnetic heads 2 and 3 scan the hatched overlap region of each track 108, 109, 110, . . . shown in FIG.

During this PCM post-recording, the magnetic head 2
, 3, a video signal is reproduced from the magnetic tape 1, and a PCM audio signal is recorded on the magnetic tape 1. The recording of the PCM audio signal is performed as follows.

That is, the audio signal input from the input terminal 12 is converted into a time-base compressed PCM audio signal by the recording PCM audio signal processing circuit 11, and then the audio signal is input from the input terminal 10.
A pilot signal necessary for tracking control during playback supplied from the adder circuit 9 is added to the recording/playback amplifier 5.
After being amplified, the signal is supplied to the magnetic heads 2 and 3 via the rotary transformer 4 and recorded on the magnetic tape 1. On this magnetic tape 1, such a PCM audio signal is
The data is recorded in the hatched overlap area of each track 108, 109, 110, . . . shown in FIG.

Most of the reproduction of the video signal is the same as the normal reproduction described above, but the following operations are performed during a predetermined period including a period in which crosstalk due to the PCM audio signal occurs in the rotary transformer 4.

The video signal supplied from the recording/reproducing amplifier 5 to the mute circuit 16 is muted because the PCM audio signal is mixed in as a crosstalk component during the overlap period in which the PCM audio signal is recorded by the rotary transformer 4. The circuit 16 uses the PCM gate signal from the input terminal 47 to mute the input video signal during the period in which the crosstalk component is mixed. The FM luminance signal of the output video signal of the mute circuit 16 is demodulated by the FM demodulation circuit 20 and supplied to the mute circuit 25, as in the above-described normal reproduction.

The mute circuit 25 mutes the input luminance signal during the period of the mute signal from the input terminal 48. FIG. 2(a) shows the output luminance signal of the LPF 24. This brightness signal period A-B is a mute period in the mute circuit 16, but since it is difficult for the mute circuit 16 to completely mute the signal, this mute period A-B Some noise remains in the output luminance signal of the FM demodulation circuit 20,
This is demodulated and noise is generated. Further, immediately after this period AB, the operation of the frequency demodulation circuit 20 becomes unstable, resulting in a distorted waveform. Therefore, the mute circuit 25 receives the mute signal from the input terminal 48.
The luminance signal from the LPF 24 is muted during a plurality of horizontal scanning periods including this period AB. If the timing of this mute signal is arbitrary and its rising and falling edges occur in the middle of the video signal during the horizontal scanning period, the video will appear on the playback screen from the middle of the horizontal scanning to the middle of the other horizontal scanning period. When the signal is muted and the jitter of the reproduced signal is added to this, the mute start and end positions will fluctuate, making the reproduced screen unsightly. Therefore, this input terminal 4
The muting of the luminance signal in the mute circuit 25 by the mute signal from 8 is a wide one that spreads back and forth from period A-B, as shown as period CD in FIG. 2(b), and horizontal synchronization. Synchronize with the signal and set the mute start and end points to positions near the horizontal sync signal and not to appear on the screen.

The output signal of the mute circuit 25 is processed by a keyed clamp circuit 26, a nonlinear de-emphasis circuit 27, and a keyed clamp circuit 28.
Supplied on the side.

On the other hand, the DO detection circuit 21 detects the output FM luminance signal of the FM/AGC circuit 18 as a dropout during the mute period by the mute circuit 16. However, the switch 22 is closed to the H side by the mute signal from the input terminal 48, so the detection signal of the DO detection circuit 21 during this mute period is not supplied to the DO compensation circuit 29. Therefore, the DO compensation circuit 29 is closed during this mute signal period N side, and the output luminance signal of the keyed clamp circuit 28 is supplied to the noise cancellation circuit 31 and the sync separation circuit 32 through the DO compensation circuit 29. Input terminal 4
During the period of the mute signal from 8, the synchronization separation circuit 32 does not output a synchronization signal. For this reason, the clamp pulse generation circuit 34 does not generate a clamp pulse, and the keyed clamp circuits 26 and 28 do not perform a clamp operation.

The switch 33 is closed during the mute signal period H from the input terminal 48 and cuts off the output signal of the clamp pulse generation circuit 34, but this is because the mute signal period from the input terminal 48 is closed as will be described later. This is because the synchronous separation circuit 32 malfunctions and the clamp pulse generation circuit 34 erroneously generates a clamp pulse.

The functions of the switches 22, 23 and keyed clamp circuits 26, 28 will now be explained. Assume now that the switches 22 and 33 are not provided. D.O.
The detection circuit 21 determines that the muted portion of the FM luminance video signal is a dropout, and supplies a DO detection signal representing the dropout period to the DO compensation circuit 29. The longer the dropout, the longer the DO detection signal will be, but if the dropout is too long, it will not be generated halfway. This is because the DO compensation circuit 29 sequentially interpolates using the same video signal during the dropout period and one horizontal scanning period immediately before the dropout period.
This is because if this continues for too long, the reproduced image will become unnatural. However, this DO detection signal is at least 1
It has a length of about 0H. The DO compensation circuit 29 is normally closed to the N side, but when a DO detection signal is supplied from the DO detection circuit 21, it closes to the DO side and delays the luminance signal of the previous horizontal scanning period by 1H as described above. The circuit 30 repeatedly outputs the signal with a delay. As a result, as shown in FIG. 2(d), the DO compensation circuit 29 outputs a luminance signal for the same horizontal scanning period in period CE.

The output luminance signal of the DO compensation circuit 29 is supplied to the sync separation circuit 32, and as shown in FIG. 2(e), the sync signal continues to be separated during the period CE. This synchronization signal is supplied to the clamp pulse generation circuit 34, and a clamp pulse is formed from its leading edge as shown in FIG. 2(f). This clamp pulse is applied to the key clamp circuits 26 and 2.
8 and is used to clamp the synchronizing signal tip of the luminance signal output from the mute circuit 25 to a predetermined potential.

Here, since the switches 22 and 33 are not provided, the DO compensation circuit 29 operates faithfully to the DO detection signal, and the keyed clamp circuits 26 and 27 operate faithfully to the DO detection signal. When operating with a clamp pulse, the following problem occurs during the mute period by the mute circuit 25.

That is, since there is no synchronizing signal during the mute period by the mute circuit 25, the keyed clamp circuits 26 and 28 clamp the muted potential to a predetermined potential.
As shown in (c), the DC potential gradually decreases. Therefore, as shown in FIG. 2(d), immediately after the muting by the mute circuit 25 is released, the synchronizing signal tip potential drops considerably, and then gradually returns to the normal DC potential. In this way, a sag occurs before and after unmuting,
The waveform of the luminance signal is distorted.

Generally, the synchronization separation circuit uses a feedback circuit having a time constant to form a potential substantially equal to the synchronization signal tip potential of the input video signal, and uses this as a threshold voltage. Therefore, mute circuit 2
5 continues for about 40 hours and the DC potential decreases as shown in Fig. 2(c), the threshold potential becomes as shown by the broken line as shown in Fig. 2(d), and the mute is reached at time E. The potential up to the end point D drops considerably, and during this period too, it is judged as a synchronization signal and malfunctions, as shown in Fig. 2(e).
The signal shown in is output as a synchronization signal. The clamp pulse generation circuit 34 generates a clamp pulse from this synchronization signal, but since the period from time E to mute end time D in FIG. 2(d) is long, the output signal e of the synchronization separation circuit 32 during this period ' is incorrectly processed as a vertical synchronization signal.

For this purpose, in this embodiment switch 3
3 is provided to prevent the key clamp circuits 26 and 28 from operating during the mute signal period from the input terminal 48, that is, the mute period by the mute circuit 25.
is switched to the H side to prevent the clamp pulse from being supplied to the keyed clamp circuits 26 and 28.

Furthermore, a switch 22 is provided, and the input terminal 4
This switch 22 is held on the H side during the mute signal period from 8 and kept on the N side so that the DO detection signal from the DO detection circuit 21 is not supplied to the DO compensation circuit 29.
The compensation circuit 29 is stopped. This makes it possible to stop the generation of synchronization signals and clamp pulses immediately after the start of muting, and as shown in Figure 2(g), the potential remains constant during the mute period, resulting in a key clamp as shown in Figure 2(d). Can improve later sag. However, if the period in which no synchronization signal exists continues for about 40 hours, from the above,
), the threshold voltage of the synchronization separation circuit 32 gradually increases and exceeds the mute potential at point F, and as shown in FIG. 2(h), from point F to the end of mute. The pseudo synchronization signal h' with a length of up to
Further, as shown in FIG. 2(i), a clamp pulse is formed and output from the front edge of this pseudo synchronization signal h' in a clamp pulse generation circuit 34. However, since the switch 33 is closed to the H side, this clamp pulse is cut off, and as shown in FIG. 2(j), no clamp pulse is supplied to the key clamp circuits 26 and 27 during the mute signal period, resulting in malfunction. do not. Due to the above,
Even if the luminance signal is muted, the sag after key clamping as shown in FIG. 2(d) can be improved.

Further, by stopping the DO compensation circuit 29, it is possible to avoid an unnatural image on the screen caused by the line immediately before muting being repeated over several tens of hours during the dropout compensation period.

Note that the mute circuit 43 in FIG. 1 mutes the chroma signal from the reproduced chroma signal processing circuit 35 during the mute signal period from the input terminal 48.

As described above, regardless of the carrier frequency of the FM luminance signal, deterioration due to PCM dubbing can be eliminated and a stable reproduced video signal without sag can be obtained.

Note that in FIG. 1, the mute circuit 25 is
It is installed after the F24. By the way, when integrating a luminance signal processing circuit into an LSI, one pin is generally required to connect an external capacitor for the input of the key clamp circuit, and the LPF 24 is also used as a block filter to connect an external capacitor. It may become a part. Therefore, in the configuration shown in FIG. 1, the FM/AGC circuit 18 to de-emphasis circuit 23, keyed clamp circuit 26 to keyed clamp circuit 28, synchronous separation circuit 32, and noise cancel circuit 31 can be integrated into an LSI. but,
The mute circuit 25 disposed between this external capacitor and the LPF 24 inevitably becomes an external component together with the LPF 24, increasing the circuit scale. Therefore, since the same effect can be obtained if the mute circuit 25 is placed before the key clamp circuit 26, by placing the mute circuit 25 before the LPF 24 in consideration of integration, This mute circuit 25 can also be integrated into the same LSI, which has the effect of further reducing the number of parts.

Furthermore, in FIG. 1, the FM/AGC circuit 18 is placed after the peaking circuit 17, but it may be placed before the peaking circuit 17, or even before the mute circuit 16. Good too.

FIG. 3 is a block diagram showing a specific example of the recording/reproducing amplifier 5 in FIG. 1, in which 53 and 54 are switches, 55 and 56 are recording amplifiers, 57 and 58 are switches,
59 and 60 are playback amplifiers, 61 to 64 are switches, 65
, 66 is an AND gate, and 67 is an inverter.
Corresponding parts are given the same reference numerals.

In the figure, in the case of normal recording, F
Assuming that a video signal in which the M audio signal and the pilot signal are frequency multiplexed and a PCM audio signal are recorded simultaneously, this video signal is sent from the input terminal 8 to the V side of the switches 57 and 58, and the PCM audio signal is sent to the adder. 9 to switch 57,
58 are respectively supplied to the P side. As shown in FIG. 4(c), the head switching signal SW(+) from the input terminal 14 causes the magnetic head 2 to switch to each track 10 of the magnetic tape 1 shown in FIG.
8, 109, 110, . . . , it becomes "H" (high level), and when the magnetic head 3 similarly scans a 180 degree section, it becomes "L" (low level). Further, the PCM gate signal from the input terminal 47 becomes "H" when the magnetic heads 2 and 3 scan during the overlap period indicated by diagonal lines in FIG. 9, as shown in FIG. 4(e).

PCM gate signal and head switching signal SW (
+) is supplied to the AND gate 65, and as shown in FIG. 4(f), a signal CNTA which becomes "H" while the magnetic head 3 scans the above-mentioned overlap period is obtained. Further, the head switching signal SW(+) is inverted by an inverter 67, and is supplied as a signal SW(-) to the AND gate 66 together with the PCM gate signal. Output signal C of AND gate 66
NTB becomes "H" while the magnetic head 2 scans the overlap period, as shown in FIG. 4(g).

The switch 57 selects the P side when the output signal CNTB of the AND gate 66 is "H", and selects the V side when it is "L". In addition, the switch 58 is the AND gate 6
When the output signal CNTA of 5 is “H”, select the P side and “
When the switch 57 is “L”, the V side is selected.
4 shows the period during which the magnetic head 2 scans the magnetic tape 1.
A signal S1 shown in FIG. 4(a) is obtained, and a signal S2 shown in FIG. 4(b) is obtained from the switch 58 during the period when the magnetic head 3 scans the magnetic tape 1. In the normal recording mode, since the post-recording mode signal AF is not supplied from the input terminal 15, the switches 63 and 64 are fixed to the N side. A mode signal representing the recording mode from the input terminal 13 is supplied to the switches 53, 54 through the switches 63, 64, thereby fixing these switches 53, 54 to the R side. Therefore, the output signal S1 of the switches 57, 58
, S2 are amplified by recording amplifiers 55 and 56, respectively, and then
The signals are supplied to the magnetic heads 2 and 3 via switches 53 and 54, and the video signal and PCM audio signal are recorded on the magnetic tape in the track pattern shown in FIG.

Next, the case of normal playback will be explained. Even in this case, the switches 63 and 64 are fixed to the N side. The mode signal from the input terminal 13 indicates the reproduction mode, and thereby the switches 53 and 54 are fixed to the P side. The reproduced signal from the magnetic head 2 passes through the switch 53, is amplified by the reproduction amplifier 59, and is supplied to the H side of the switch 61 and the L side of the switch 62, and the reproduced signal from the magnetic head 3 passes through the switch 54 and is amplified by the reproduction amplifier 59. The signal is amplified by an amplifier 60 and supplied to the L side of a switch 61 and the H side of a switch 62. The switches 61 and 62 are connected to the inverter 6, respectively.
The head switching signal SW(+) is controlled by the output signal SW(-) of 7 and the head switching signal SW(+).
When it is "H", it is closed to the H side, and when it is "L", it is closed to the L side.As a result, the reproduced PCM audio signals from the magnetic heads 2 and 3 are extracted by the switch 61, and the reproduced video signals from the magnetic heads 2 and 3 are The signal is extracted from the switch 62. That is, the switches 62 and 63 select the output signals of the magnetic heads 2 and 3 according to the polarity of the head switching signal (+), and separate the video signal and the PCM audio signal.

Next, the case of dubbing will be explained. In this case, the control of the switches 53 and 54 is different from that for recording and reproduction described above. As is clear from FIG. 4(a), in the video signal period, the head switching signal SW(+) (FIG. 4(a)
c)) and the output signal SW(-) of the inverter 67 (Fig. 4(
At timing d)), the switches 53 and 54 may be set to the P side to set the playback mode, and during the PCM audio signal period, the switches 53 and 54 may be set to the P side to set the recording mode during the PCM gate signal period from the input terminal 47. That is, switch 53
is the output signal CNT of the AND gate 66 shown in FIG. 4(g).
During the "H" period of B, the switch 53 is R during the period when the output signal CNTA of the AND gate 65 is "H" shown in FIG. 4(f).
and close to the P side during each "L" period.

By the way, when recording and reproducing are performed simultaneously in this way, the recorded PCM audio signal (
Since the amplitude of FIG. 4(h)) is very large, the recorded PCM audio signal crosstalks with the reproduced video signal in the rotary transformer 4 as described above, and the output signals of the reproduction amplifiers 59 and 60 are The signals shown in i) and (j) are obtained, and when both are selected by switching with the switch 62, the reproduced signal shown in FIG. 4(k) is obtained.

FIG. 5 is a block diagram showing a specific example of the mute circuit 25 in FIG. 1, in which 68 is a switch;
9 is a variable DC voltage source, and parts corresponding to those in FIG. 1 are given the same reference numerals.

In the figure, the mute from the input terminal 48
When the output signal is “L”, the switch 68 is closed to the L side, and the switch 68 is closed to the L side.
The brightness signal from the PF 24 is output via the switch 68. When the mute signal is “H”, the switch 68
is closed to the H side, and instead of the brightness signal from the LPF 24, the preset DC potential of the variable DC power supply 69 is applied to the switch 6.
8.

FIG. 6 is a block diagram showing another specific example of the mute circuit 25 in FIG. 1, in which 70 is a switch;
71 is a resistor, 72 is a capacitor, and 73 is a switch, and parts corresponding to those in FIG. 1 are given the same symbols.

In the figure, a resistor 71 and a capacitor 72
constitutes an APL detection circuit, and when the mute signal from the input terminal 48 is "L", the switch 73 is closed to the L side, similar to the specific example of FIG. 5, and the luminance signal from the LPF 24 is directly transmitted. Output. At this time, the switch 70 is also closed to the L side, and the capacitor 7 is connected to the H side of the switch 73.
The APL potential of the luminance signal from the LPF 24 obtained at 2 is supplied.

When the mute signal becomes "H", both switches 70 and 73 close to the H side. As a result, the switch 73 selects the APL potential held in the capacitor 72 immediately before the mute signal becomes "H", and outputs this APL potential instead of the luminance signal from the LPF 24.

FIG. 7 is a block diagram showing another embodiment of the magnetic recording/reproducing apparatus according to the present invention, in which 74 is a DO detection circuit, 75 is a clamp pulse generation circuit, 76 is a synchronizing signal insertion circuit, 77 is a switch, Reference numeral 78 denotes an input terminal for an additional synchronization signal, and parts corresponding to those in FIG.

This embodiment differs from the embodiment shown in FIG. 1 in that a DO detection circuit 74 and a clamp pulse generation circuit 75
operation, synchronization signal insertion circuit 76, switch 77
This is the addition of .

The operation of this embodiment during post-recording will be explained below.

As in the embodiment shown in FIG. 1, when a video signal is reproduced from the magnetic tape 1 by the magnetic heads 2 and 3 during post-recording, the mute signal from the input terminal 48 mutes the video signal. During the period in which the reproduced video signal is muted in the circuit 25, an additional synchronization signal is input from the input terminal 78, and the DO detector 74 stops operating due to this mute signal. As a result, the DO compensation circuit 29 closes to the N side and stops the DO compensation operation, similar to the embodiment shown in FIG. Similarly to the embodiment shown in FIG. 1, the synchronization separation circuit 32 malfunctions due to the rise in the threshold potential and outputs a pseudo synchronization signal. However, the clamp pulse generation circuit 75 has stopped its clamp pulse generation operation due to the mute signal from the input terminal 48, and therefore the key clamp circuits 26, 2
8, similarly to the embodiment shown in FIG. 1, allows the input luminance signal to pass through as is and does not malfunction.

The output luminance signal of the noise canceling circuit 31 is supplied to a synchronizing signal insertion circuit 76, and an additional synchronizing signal supplied from an input terminal 78 via a switch 77 is added thereto. The luminance signal of the synchronization signal insertion circuit 76 is output from the output terminal 5.
3 and is output to the adder 44.

According to this embodiment, the same effect as the embodiment shown in FIG. 1 can be obtained without providing a switch in the clamp pulse transmission path and the control signal transmission path of the DO compensation circuit. Furthermore, since the synchronization signal is added to the mute period of the luminance signal, the horizontal synchronization of the monitor is stabilized, skew on the screen does not occur, and the image quality during post-recording is improved.

Note that this embodiment can also be modified in the same way as the embodiment shown in FIG. Further, although the synchronization signal insertion circuit 76 is arranged after the noise canceling circuit 31, it is sufficient that it is after the mute circuit 25. In particular, the output signal of the synchronization signal insertion circuit 76 is also placed in the synchronization separation circuit 32. By supplying the synchronization signal, the continuous composite synchronization signal can be separated from the synchronization separation circuit 32.

[0062]

[Effects of the Invention] As explained above, according to the present invention,
By simply adding a simple circuit to the conventional circuit, it is possible to eliminate crosstalk from the PCM audio signal to the video signal during PCM dubbing, regardless of the frequency of the FM brightness signal, and to generate a stable video signal without sag. Can be played.

Furthermore, the present invention has a configuration suitable for integrating a luminance signal processing circuit, and integration is possible by simply adding a simple and small-scale circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic recording/reproducing apparatus according to the present invention.

FIG. 2 is a waveform diagram showing signals at various parts in FIG. 1;

FIG. 3 is a block diagram showing a specific example of the recording/reproducing amplifier in FIG. 1;

FIG. 4 is a diagram showing the timing relationship of signals of each part in FIG. 3;

[Fig. 5] Mutator after the low-pass filter in Fig. 1
FIG. 2 is a block diagram showing a specific example of a circuit.

[Fig. 6] Mutator after the low-pass filter in Fig. 1
FIG. 3 is a block diagram showing another specific example of the gate circuit.

FIG. 7 is a block diagram showing another embodiment of the magnetic recording/reproducing apparatus according to the present invention.

FIG. 8 is a plan view showing the positional relationship between the rotating cylinder and the magnetic tape.

FIG. 9 is a schematic diagram showing a track pattern on a magnetic tape.

[Explanation of symbols]

11 PCM audio signal processing circuit 16 Mute circuit 21 Dropout detection circuit 22 Switch 25 Mute circuit 26, 28 Keyed clamp circuit 29 Dropout compensation circuit 32 Synchronization separation circuit 33 Switch 34 Clamp pulse generation circuit 48 Mute signal input terminal 74 Dropout detection circuit 75 Clamp pulse generation circuit. 76 Synchronous signal insertion circuit

Claims (9)

[Claims] Claim 1: A magnetic tape is wound around a rotating cylinder equipped with at least two magnetic heads at least 180 degrees and run, and one of the magnetic heads runs on the magnetic tape to generate a video signal. is recorded as a frequency multiplexed signal of a frequency-modulated luminance signal and a frequency-converted color signal,
In a helical scan type magnetic recording/reproducing device having a first period for reproducing and a second period for simultaneously running the magnetic tape, one of the two magnetic heads runs the first period. When a video signal already recorded on the magnetic tape is reproduced in a period of , and the other magnetic head records another information signal in the second period, the period of In the third period, which is wider before and after the second period, a first means for stopping the operation of a keyed clamp circuit for clamping the reproduced luminance signal, and a first means for stopping the operation of the keyed clamp circuit that clamps the reproduced luminance signal, and 1. A magnetic recording and reproducing apparatus, comprising: second means for muting a signal. 2. The magnetic recording and reproducing apparatus according to claim 1, further comprising third means for muting the reproduced chroma signal during the third period. 3. In claim 1 or 2, the third
A fourth step for stopping the operation of the dropout compensation circuit for a period of
A magnetic recording/reproducing device characterized by having means. 4. A magnetic recording device according to claim 1, wherein said second and third means replace said third period reproduced luminance signal and reproduced chroma signal with a predetermined DC potential. playback device. 5. In claim 1, 2 or 3, the second means reproduces the third period reproduced luminance signal from the third period.
A magnetic recording/reproducing apparatus characterized in that the reproduction brightness signal is replaced with an APL potential of the reproduction luminance signal immediately before the period. 6. According to claim 1, 2, 3, 4 or 5, the first means is means for cutting off a path from the clamp pulse generating means to the key clamp circuit. Recording and playback device. 7. The magnetic recording and reproducing apparatus according to claim 1, wherein the first means is means for stopping the operation of the clamp pulse generating means. 8. A magnetic recording and reproducing apparatus according to claim 3, wherein said fourth means is means for cutting off a path from dropout detection means to said dropout compensation circuit. 9. A magnetic recording and reproducing apparatus according to claim 3, wherein said fourth means is means for stopping dropout detection means.