JP2875642B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal and a PC
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus for performing overlap recording of M audio signals, and more particularly to a magnetic recording / reproducing apparatus capable of after-recording (hereinafter, referred to as "after-recording").

[0002]

2. Description of the Related Art For example, in an 8 mm video standard VTR, as shown in FIG. 8, magnetic heads 103 and 104 for recording / reproducing are provided on a rotary cylinder 102 at an angular interval of 180 degrees. , 104, a flying erase head 105 is mounted, respectively, and the tape guides 106, 107 cause a magnetic tape 1 to be mounted.
01 is wound around the rotary cylinder 102 by about 216 degrees, and the two magnetic heads 103 and 104 simultaneously compress the time axis into a 36-degree area on the taped side where the magnetic tape 101 is scanned. The video signals are alternately recorded by the magnetic heads 103 and 104 in the remaining 180-degree area. 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 36-degree section with the formed tracks 108, 109, 110,... Is a recording area for PCM audio signals.
The 180-degree section shown in white is a recording area of the video signal. In such a tape format, it is possible to perform post-recording (hereinafter referred to as PCM post-recording) for recording a PCM audio signal in a 36-degree section while reproducing a video signal from a 180-degree section.

At the time of this PCM dubbing, a recorded PCM audio signal having a large amplitude crosstalks with a reproduced video signal having a small amplitude in the rotary transformer, and the reproduced video signal is deteriorated. Therefore, the mitigation measures are described in, for example, JP-A-63-1
No. 87782.

Here, in the 8 mm video standard, the luminance signal is frequency-modulated so that the frequency increases on the white side.
A mode in which the carrier frequency of a 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);
The carrier frequency of the luminance signal is 5.7 MHz to 7.7 MH
z (hereinafter referred to as a high band mode). In the low band mode, the center frequency of the PCM audio signal is higher than that of the FM luminance signal. Therefore, when the cross-talked PCM audio signal is frequency-demodulated, it becomes noise having a DC level higher than the 100% white level of the video signal. From this, A of the reproduced luminance signal
By detecting the PL (Average Picture Levl), it is possible to detect and clip the crosstalked PCM audio signal portion.

[0006]

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

In a recording luminance signal processing circuit,
Key to clamp the tip of the synchronization signal before the frequency modulator
Although a clamp circuit is provided, the key is also used during playback.
No consideration has been given to processing the reproduced luminance signal using the Doclamp circuit.

An object of the present invention is to provide a magnetic recording / reproducing apparatus which can reduce crosstalk even in a high band mode at the time of PCM dubbing, and which can use a key clamp circuit at the time of reproduction to reduce deterioration of a reproduced video signal. It is in.

[0009]

In order to achieve the above object, the present invention provides means for stopping the operation of a key clamp circuit during a period in which a PCM audio signal crosses during PCM dubbing. At least one means for muting the reproduced luminance signal is provided at a stage preceding the key clamp circuit.

[0010]

During PCM dubbing, during a period in which a PCM audio signal is cross-talked, the video signal is degraded due to the presence of noise or the like, so that the video signal is muted. Further, during this period, the operation of the key clamp circuit is stopped to prevent the occurrence of sag by clamping the muted video signal.

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

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention, wherein 1 is a magnetic tape, 2 and 3 are magnetic heads, 4 is a rotary transformer, 5 is a recording / reproducing amplifier, and 6 is a control. A signal generation circuit, 7 is an output terminal of a reproduced PCM audio signal, 8 is an input terminal of a recording video signal, 9 is an adder,
Reference numeral 10 denotes a pilot signal input terminal, 11 denotes a recording PCM audio signal processing circuit, 12 denotes an audio signal input terminal, 13 denotes a mode signal input terminal, 14 denotes a head switching signal input terminal, and 15 denotes an after-recording mode signal input. Terminal, 16 is a mute circuit, 17 is a peaking circuit, 18 is FM / AGC
(Automatic gain control circuit) circuit, 19 is a limiter, 20 is a frequency demodulation circuit, 21 is a DO (dropout) detection circuit, 22 is a switch, 23 is a de-emphasis circuit, 2
4 is an LPF (low-pass filter), 25 is a mute circuit, 26 is a key clamp circuit, 27 is a non-linear deemphasis circuit, 28 is a key clamp circuit, and 29 is DO.
A compensation circuit, 30 is a 1H (H is one horizontal scanning period) delay line,
31 is a noise cancellation circuit, 32 is a synchronization separation circuit, 3
3 is a switch, 34 is a clamp pulse generation circuit, 35 is a reproduced chroma signal processing circuit, 36 is an LPF, and 37 is 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, 4
6 is a reproduction FM audio signal processing circuit, 47 is an input terminal of a PCM gate signal, 48 is an input terminal of a mute signal, 49 is an output terminal of an FM audio signal, 50 is an output terminal of a chroma signal, and 51 is a composite signal. An output terminal for a video signal and an output terminal 52 for a luminance signal are provided.

Next, the operation of this embodiment will be described.

In the case of ordinary recording, a pilot signal for tracking control during reproduction from the input terminal 8 or an F signal is used.
The video signal in which the M audio signals are multiplexed
After that, the signal is supplied to the magnetic heads 2 and 3 via the rotary transformer 4 and recorded on the magnetic tape 1. In this case, the video signal is a signal obtained by multiplexing an FM luminance signal and a low-frequency-converted chroma signal, to which an FM audio signal is further multiplexed. Recording / playback amplifier 5
Is in the recording mode by the control signal generation circuit 6 in accordance with the mode signal from the input terminal 13 and is controlled in accordance with the head switching signal SW (+) from the input terminal 14.

In the case of normal reproduction, the recording / reproduction amplifier 5
Is set to a reproduction mode by a mode signal from the input terminal 13 and is controlled according to a 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 supplied from the input terminal 47, and the after-recording mode signal AF is not supplied from the input terminal 15, respectively.
Does not perform the mute operation, and allows the input signal to pass as it is, and the switches 22 and 33 are closed to the L side.

In this state, the video signal reproduced from the magnetic tape 1 by the magnetic heads 2 and 3 is amplified by the recording / reproducing amplifier 5 through the rotary transformer 4 and then passes through the mute circuit 16 and its FM. The luminance signal is equalized by the peaking circuit 17, processed by the FM / AGC circuit 18 and the limiter 19, and supplied to the 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 is further processed by a keyed clamp circuit 26,
The N of the DO compensation circuit 29 which is processed by the nonlinear de-emphasis circuit 27 and the keyed clamp circuit 28 and is a switch.
Supplied to the side.

On the other hand, the FM luminance signal output from the FM / AGC circuit 18 is supplied to a DO detection circuit 11 where a dropout is detected.
It is used for controlling the compensation circuit 29.

The DO compensation circuit 29 is normally closed on the N side, and the output luminance signal of the keyed clamp circuit 28 is
The signal is supplied to the noise canceling circuit 31 and the synchronization separating circuit 32 through the compensating circuit 29 and the 1H delay circuit 3
The signal is delayed by 0 and supplied to the DO side of the DO compensation circuit 29. When the DO detection circuit 21 detects a dropout,
The DO compensation circuit 29 closes to the DO side during the signal period (dropout period) of the detection signal. Thus, the dropout period 1H of the output luminance signal of the keyed clamp circuit 28
The compensation is made by the luminance signal 1H before from the delay circuit 30, and the dropout is compensated.

The sync separation circuit 32 separates a sync signal from the luminance signal from the DO compensation circuit 29. This synchronizing signal is used as is well known, but is also supplied to a clamp pulse generating circuit 34, and a clamp pulse is generated 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 an output terminal 52 and supplied to an adding circuit 44.

The output video signal of the mute circuit 16 is AC
The signal is supplied to a well-known reproduced chroma signal processing circuit 35 including a C circuit 37 and a frequency conversion circuit 38, and a BPF 45. The BPF 45 separates the FM audio signal added to the video signal, and the FM audio signal is subjected to processing such as demodulation in a reproduction FM audio signal processing circuit 46 and output from an 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 an adjacent track. The chroma signal is added via the color killer switch 42 and the mute circuit 43. And output terminal 50.
The addition circuit 44 adds the luminance signal and the chroma signal,
It is output from the output terminal 51 as a composite video signal.

Next, the operation at the time of PCM post-recording will be described. In this case, the recording / reproducing amplifier 5 enters the reproducing mode for the video signal by the mode signal from the input terminal 13, and the post-recording mode signal A from the input terminal 15
With F, the PCM audio signal enters the period recording mode of the PCM gate signal from the input terminal 47. This P
The CM gate signal indicates a period during which the magnetic heads 2 and 3 scan the hatched overlap areas of the tracks 108, 109, 110,... Shown in FIG.

At the time of this PCM dubbing, a video signal is reproduced from the magnetic tape 1 by the magnetic heads 2 and 3 and a PCM audio signal is recorded on the magnetic tape 1. It is performed as follows.

That is, the audio signal input from the input terminal 12 is converted into a PCM audio signal whose time base has been compressed by the recording PCM audio signal processing circuit 11.
A pilot signal necessary for tracking control at the time of reproduction supplied from the adder 9 is added by an adder circuit 9, and the recording / reproducing amplifier 5
After being amplified by the above, they are supplied to the magnetic heads 2 and 3 via the rotary transformer 4 and recorded on the magnetic tape 1. On the magnetic tape 1, the PCM audio signal is transmitted as shown in FIG.
Are recorded in the overlapped areas where the tracks 108, 109, 110,...

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

The video signal supplied from the recording / reproducing amplifier 5 to the mute circuit 16 has the PCM audio signal mixed as a crosstalk component during the overlap period in which the rotary transformer 4 records the PCM audio signal. The circuit 16 uses the PCM gate signal from the input terminal 47 to mute the input video signal while 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 in the same manner as in the normal reproduction described above.

The mute circuit 25 mutes the input luminance signal during the period of the mute signal from the input terminal 48. FIG. 2A shows an output luminance signal of the LPF 24. The period AB of the luminance signal is a mute period in the mute circuit 16, but it is difficult for the mute circuit 16 to completely mute the signal. Some noise remains in the output luminance signal of the FM demodulation circuit 20,
This is demodulated to generate noise. Immediately after this period AB, the operation of the frequency demodulation circuit 20 becomes unstable, so that the waveform is distorted. Therefore, the mute circuit 25 uses the mute signal from the input terminal 48 to
The luminance signals from the plurality of horizontal scanning periods LPF 24 including the period AB are muted. If the timing of this mute signal is arbitrary and its rising and falling edges are in the middle of the video signal during the horizontal scanning period, the video is displayed on the playback screen from the middle of the horizontal scanning to the middle of another horizontal scanning period. The signal is muted, and if the jitter of the reproduction signal is added to the signal, the start and end positions of the mute fluctuate, making the reproduction screen unsightly. Therefore, this input terminal 4
The mute of the luminance signal in the mute circuit 25 by the mute signal from FIG. 8 is a wide one that extends before and after the period AB as shown in a period CD in FIG. In synchronization with the signal, the start and end points of the mute are near the horizontal synchronization signal and do not appear on the screen.

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

On the other hand, the DO detection circuit 21 detects the FM luminance signal output from the FM / AGC circuit 18 as a mute period dropout 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 that 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 on the side of the mute signal period N, and the output luminance signal of the keyed clamp circuit 28 is supplied to the noise cancellation circuit 31 and the synchronization separation circuit 32 through the DO compensation circuit 29. Input terminal 4
The period synchronization separation circuit 32 of the mute signal from No. 8 does not output the 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.

Note that the switch 33 is closed on the side of the mute signal period H from the input terminal 48 and cuts off the output signal of the clamp pulse generation circuit 34. This is because the sync separation circuit 32 malfunctions and the clamp pulse generation circuit 34 erroneously generates a clamp pulse.

The operation of the switches 22, 23 and the keyed clamp circuits 26, 28 will now be described. Now, it is assumed that the switches 22 and 33 are not provided. DO
The detection circuit 21 determines that the muted portion of the FM luminance video signal is a dropout, and supplies a DO detection signal indicating a dropout period to the DO compensation circuit 29.
The DO detection signal is longer as the dropout is longer, but if the dropout is too long, it is not generated on the way. This is because the DO compensation circuit 29 sequentially interpolates with the same video signal in one horizontal scanning period immediately before the dropout period.
This is because if this is performed for a long time, the reproduced image becomes unnatural. However, this DO detection signal is at least one.
There is a length of about 0H. Although the DO compensation circuit 29 is normally closed on the N side, when the DO detection signal is supplied from the DO detection circuit 21, it is closed on the DO side, and as described above, the luminance signal of the immediately preceding horizontal scanning period is delayed by 1H. The signal is repeatedly output while being delayed by the circuit 30. As a result, as shown in FIG. 2D, the DO compensation circuit 29 outputs a luminance signal in the same horizontal scanning period in the period CE.

The output luminance signal of the DO compensation circuit 29 is supplied to the synchronization separation circuit 32, and the synchronization signal continues to be separated during the period CE as shown in FIG. This synchronization signal is supplied to the clamp pulse generation circuit 34, and a clamp pulse is formed from the leading edge thereof as shown in FIG. This clamp pulse is supplied to a key clamp circuit 26,
28, and is used to clamp the leading end of the synchronizing signal 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 compensating circuit 29 operates faithfully to the DO detection signal, and the keyed clamp circuits 26 and 27 operate from the clamp pulse generating circuit 34. When operated by the clamp pulse, the following problem occurs during the mute period by the mute circuit 25.

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

In general, the sync separation circuit forms a potential substantially equal to the tip potential of the sync signal of the input video signal by a feedback circuit having a time constant, and uses this as a threshold voltage. Therefore, when the mute by the mute circuit 25 continues for about 40 H and the DC potential decreases as shown in FIG. 2C, the threshold potential becomes as shown by a broken line as shown in FIG.
The potential between the time point E and the mute end time point D is considerably reduced. During this period, the signal is determined to be a synchronization signal and malfunctions.
A signal as shown in (e) is output as a synchronization signal. The clamp pulse generation circuit 34 generates a clamp pulse from the synchronization signal. However, since the period from the point E in FIG. 2D to the end point M of the mute is long, the output signal e of the synchronization separation circuit 32 during this period is long. 'Is erroneously processed as a vertical synchronization signal.

For this reason, in this embodiment, the switch 3
The switch 33 is provided so that the mute signal period from the input terminal 48, that is, the mute period by the mute circuit 25, and the key clamp circuits 26 and 28 do not operate.
To the H side so that the clamp pulse is not supplied to the keyed clamp circuits 26 and 28.

Further, a switch 22 is provided, and the input terminal 4
8, the switch 22 is held on the H side, and the DO detection signal from the DO detection circuit 21 is not supplied to the DO compensation circuit 29 and is held on the N side.
The compensation circuit 29 is stopped. As a result, the generation of the synchronizing signal and the clamp pulse can be stopped immediately after the start of the mute, and the potential becomes constant during the mute period as shown in FIG. 2 (g), and the key clamp as shown in FIG. 2 (d). Later sag can be improved. However, if the period during which no synchronizing signal is present continues for about 40H, the above results indicate that FIG.
2 (g), the threshold voltage of the sync separation circuit 32 gradually rises this time and exceeds the mute potential at the point F. As shown in FIG. A pseudo synchronizing signal h 'having a length up to the end point is output from the synchronizing separation circuit 32, and further, as shown in FIG.
A clamp pulse is formed and output from the leading edge of '.
However, since the switch 33 is closed to the H side, this clamp pulse is cut off, and the clamp pulse is not supplied to the mute signal period key clamp circuits 26 and 27 as shown in FIG. do not do. From the above,
Even if the luminance signal is muted, the sag after the key clamp as shown in FIG. 2D can be improved.

Further, by stopping the DO compensation circuit 29, the unnaturalness of the picture on the screen caused by the repetition of the line immediately before the mute for the dropout compensation period of several tens of H can be avoided.

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 is eliminated, and a stable reproduced video signal without sag can be obtained.

In FIG. 1, the mute circuit 25 is connected to the LP
Installed after F24. When a luminance signal processing circuit is integrated into an LSI, generally, one pin is required to connect an external capacitor for inputting a key clamp circuit, and the LPF 24 is externally provided as a block filter. May be a part. Therefore, in the configuration shown in FIG. 1, the FM / AGC circuit 18 to the de-emphasis circuit 23, the keyed clamp circuit 26 to the keyed clamp circuit 28, the synchronization separation circuit 32, and the noise cancellation circuit 31 can be integrated into an LSI. However, the mute circuit 25 disposed between the external capacitor and the LPF 24 is necessarily an external component together with the LPF 24, and the circuit scale is increased. Therefore, mu
Since the same effect can be obtained if the mute circuit 25 is located at a stage prior to the key clamp circuit 26, the mute circuit 25 is arranged at a stage prior to the LPF 24 in consideration of integration. Can be integrated on the same LSI, and the number of parts can be further reduced.

In FIG. 1, the FM / AGC circuit 18 is disposed after the peaking circuit 17. However, the FM / AGC circuit 18 is disposed before the peaking circuit 17 and further before the mute circuit 16. Is also good.

FIG. 3 is a block diagram showing a specific example of the recording / reproducing amplifier 5 in FIG. 1, wherein 53 and 54 are switches, 55 and 56 are recording amplifiers, 57 and 58 are switches,
59 and 60 are reproduction amplifiers, 61 to 64 are switches, 6
Reference numerals 5 and 66 denote AND gates, and 67 denotes an inverter. The parts corresponding to those in FIG.

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, the video signal is transmitted from the input terminal 8 to the switches 57 and 58.
, The PCM audio signal from the adder 9 to the switch 5
7 and 58 are supplied to the P side, respectively. As shown in FIG. 4 (c), the head switching signal SW (+) from the input terminal 14 indicates that the magnetic head 2 has a 180-degree section of each of the tracks 108, 109, 110,. When scanning, "H" (high level), the magnetic head 3
It becomes "L" (low level) when scanning in the 0 degree section. The PCM gate signal from the input terminal 47 is shown in FIG.
As shown in (e), when the magnetic heads 2 and 3 scan in the overlapped period shown in FIG.

PCM gate signal and head switching signal SW
The signal (+) is supplied to the AND gate 65, and as shown in FIG. 4F, a signal CNTA which becomes "H" while the magnetic head 3 scans the overlap period is obtained. The head switching signal SW (+) is inverted by the inverter 67,
The signal SW (−) is supplied to the AND gate 66 together with the PCM gate signal. As shown in FIG. 4G, the output signal CNTB of the AND gate 66 becomes “H” while the magnetic head 2 scans the overlap period.

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 the output signal CNTB is "L". The switch 58 is connected to the AND gate 6
When the output signal CNTA of No. 5 is “H”, the P side is selected,
When "L", the V side is selected. Therefore, switch 5
7 shows the signal S1 shown in FIG. 4A during the period when the magnetic head 2 scans the magnetic tape 1, and the switch 58 shows the signal S1 during the period when the magnetic head 3 scans the magnetic tape 1 from the switch 58.
Is obtained. 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. When the mode signal indicating the recording mode from the input terminal 13 is supplied to the switches 53 and 54 through the switches 63 and 64, the switches 53 and 54 are fixed to the R side. Therefore, the output signal S of the switches 57 and 58
1 and S2 are amplified by recording amplifiers 55 and 56, respectively, and then supplied to the magnetic heads 2 and 3 via the switches 53 and 54. The video signals and the PCM audio signals are recorded on the magnetic tape in the track pattern shown in FIG. Is recorded.

Next, the case of normal reproduction will be described. Also 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, whereby the switches 53 and 54 are fixed to the P side. The reproduction signal of the magnetic head 2 is amplified by the reproduction amplifier 59 through the switch 53 and supplied to the H side of the switch 61 and the L side of the switch 62. The reproduction signal of the magnetic head 3 is reproduced through the switch 54. The signal is amplified by the amplifier 60 and supplied to the L side of the switch 61 and the H side of the switch 62. The switches 61 and 62 output the output signal SW (−) of the inverter 67 and the head switching signal SW (+), respectively.
However, when the head switching signal SW (+) is "H", it is closed on the H side, and when it is "L", it is closed on 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 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 post-recording will be described.
In this case, the control of the switches 53 and 54 is different from the above-described recording and reproduction. As is clear from FIG. 4A, during the video signal period, the head switching signal SW (+) (FIG.
(C)) and the output signal SW (−) of the inverter 67 (FIG.
At the timing of (d), the switches 53 and 54 are set to the P side to set the reproduction mode, and during the PCM audio signal period, the input terminal 47 is set.
The PCM gate signal period switches 53 and 54 may be set to the P side to set the recording mode. That is, the switch 5
3 is an output signal CN of the AND gate 66 shown in FIG.
During the “H” period of TB, the switch 53 closes to the R side while the output signal CNTA of the AND gate 65 shown in FIG. 4F is “H” and closes to the P side during the “L” period.

When recording and reproduction are performed simultaneously as described above, the amplitude of the recorded PCM audio signal (FIG. 4 (h)) is much larger than that of the reproduced video signal. Then, the recorded PCM audio signal crosstalks with the reproduced video signal, and the output signals of the reproducing amplifiers 59 and 60 become signals as shown in FIGS.
When both are switched and selected by the switch 62, FIG.
The reproduction signal shown in FIG.

FIG. 5 is a block diagram showing a specific example of the mute circuit 25 in FIG.
Reference numeral 9 denotes a variable DC voltage source, and portions corresponding to those in FIG.

Referring to FIG.
When the reset signal is “L”, the switch 68 closes to the L side,
The luminance 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 luminance signal from the LPF 24, a preset DC potential of the variable
8 is output.

FIG. 6 is a block diagram showing another specific example of the mute circuit 25 in FIG.
Reference numeral 71 denotes a resistor, reference numeral 72 denotes a capacitor, reference numeral 73 denotes a switch, and portions corresponding to those in FIG.

In the figure, a resistor 71 and a capacitor 72
Constitutes an APL detection circuit. When the mute signal from the input terminal 48 is at "L", the switch 73 is closed to the L side as in the specific example of FIG. 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.
2 is supplied with the APL potential of the luminance signal from the LPF 24 obtained.

When the mute signal becomes "H", the switches 70 and 73 are both closed 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 synchronization signal insertion circuit, 77 is a switch, Numeral 78 denotes an input terminal for an additional synchronization signal, and portions corresponding to those in FIG.

This embodiment differs from the embodiment shown in FIG. 1 in that the DO detection circuit 74 and the clamp pulse generation circuit 75
Operation, the synchronization signal insertion circuit 76, the switch 77
Is added.

The operation of this embodiment at the time of post-recording will be described.

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 at the time of after-recording, a mute signal from the input terminal 48 mutes. During the period when the reproduced video signal is muted by the circuit 25, an additional synchronizing signal is inputted from the input terminal 78, and the DO detector 74 is provided by the muting signal.
Stops operation. Thereby, the DO compensation circuit 29
As in the embodiment shown in FIG. 1, the valve is closed on the N side to stop the DO compensation operation. As in the embodiment shown in FIG. 1, the synchronizing separation circuit 32 malfunctions due to the rise of the threshold voltage and outputs a pseudo synchronizing signal. However, the clamp pulse generation circuit 75 is connected to the input terminal 48
, The clamp pulse generation operation is stopped by the mute signal from the
Reference numeral 28, like the embodiment shown in FIG. 1, allows the input luminance signal to pass as it is and does not malfunction.

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

According to this embodiment, the same effects as those of the embodiment shown in FIG. 1 can be obtained without providing a switch in the transmission path of the clamp pulse and the transmission path of the control signal of the DO compensation circuit. Furthermore, since the synchronization signal is also added during the mute period of the luminance signal, there is an effect that the horizontal synchronization of the monitor is stabilized, no skew occurs on the screen, and the image quality during after-recording is improved.

Note that this embodiment can be modified in the same manner as the embodiment shown in FIG. Further, the synchronization signal insertion circuit 76 is disposed after the noise cancellation circuit 31. However, the synchronization signal insertion circuit 76 may be provided after the mute circuit 25. In particular, the output signal of the synchronization signal insertion circuit 76 is also output to the synchronization separation circuit 32. By supplying the composite sync signal, a continuous composite sync signal can be separated from the sync separation circuit 32.

[0062]

As described above, according to the present invention,
By simply adding a simple circuit to the conventional circuit, at the time of PCM dubbing, the crosstalk from the PCM audio signal to the video signal is removed regardless of the frequency of the FM luminance signal, and a stable video signal without sag is obtained. Can be played.

The present invention has a configuration suitable for integration of a luminance signal processing circuit, and can be integrated simply by adding a simple and small-scale circuit.

[Brief description of the 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 chart showing signals of respective units in FIG.

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

FIG. 4 is a diagram showing a timing relationship of signals of respective units in FIG. 3;

FIG. 5 is a diagram illustrating a mu-stage in a stage following the low-pass filter in FIG. 1;
FIG. 3 is a block diagram illustrating a specific example of a gate circuit.

FIG. 6 is a diagram illustrating a mu-stage in a stage following the low-pass filter in FIG. 1;
FIG. 14 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 a positional relationship between a rotary cylinder and a magnetic tape.

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

[Explanation of symbols]

 Reference Signs List 11 PCM audio signal processing circuit 16 Mute circuit 21 Dropout detection circuit 22 Switch 25 Mute circuit 26, 28 Key clamp circuit 29 Dropout compensation circuit 32 Synchronous 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

Continuation of the front page (72) Inventor Akifumi Tabata 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Within Hitachi Image Information System Co., Ltd. (56) References JP-A-61-289791 (JP, A) (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H04N 5/91, 9/79-9/898

Claims (9)

(57) [Claims] 1. A magnetic tape is wound around a rotary cylinder carrying at least two magnetic heads by rotating it by 180 degrees or more, and one of the magnetic heads runs on the magnetic tape to produce a video signal. Has a first period in which recording and reproduction are performed as a frequency multiplexed signal of a frequency-modulated luminance signal and a frequency-converted color signal, and a second period in which the two magnetic heads run on a magnetic tape at the same time. In a helical scan type magnetic recording / reproducing apparatus, one of the two magnetic heads reproduces a video signal already recorded on a magnetic tape in the first period, and the other magnetic head is a second magnetic head. When another information signal is recorded during the period, a key clamp circuit for clamping the reproduced luminance signal during a third period that is equal to the second period or is extended before and after the second period. Stop operation A magnetic recording / reproducing apparatus comprising: a first means for causing a signal to be reproduced; and a second means for muting the reproduced luminance signal at a stage preceding the key clamp circuit. 2. The magnetic recording / reproducing apparatus according to claim 1, further comprising third means for muting the reproduced chroma signal during the third period. 3. The magnetic recording / reproducing apparatus according to claim 1, further comprising: fourth means for stopping the operation of the dropout compensation circuit during the third period. 4. The magnetic recording apparatus according to claim 1, wherein said second and third means replace a reproduced luminance signal and a reproduced chroma signal with a predetermined DC potential during said third period. Playback device. 5. The apparatus according to claim 1, wherein the second means replaces the reproduced luminance signal in the third period with an APL potential of the reproduced luminance signal immediately before the third period. Magnetic recording and reproducing device. 6. A magnetic device according to claim 1, wherein said first means is means for cutting off a path from a clamp pulse generating means to said key clamp circuit. Recording and playback device. 7. A magnetic recording / reproducing apparatus according to claim 1, wherein said first means is means for stopping operation of a clamp pulse generating means. 8. The method according to claim 3, wherein the fourth means includes:
A magnetic recording / reproducing apparatus, which is means for cutting off a path from a dropout detecting means to the dropout compensation circuit. 9. The method according to claim 3, wherein:
A magnetic recording / reproducing apparatus, which is means for stopping a dropout detecting means.