JPS6394407A - Video tape recorder - Google Patents

Abstract

PURPOSE:To obtain a reproducing video without disturbance by muting a reproducing video signal for a prescribed period at the time of post-recording and simultaneously, holding an AGC voltage. CONSTITUTION:A VTR 20 outputs an AGC voltage VAGC1 obtained from an AGC detecting circuit 13 through a switch circuit 21 to a variable gain amplifier 12. Further, to the output edge side of the circuit 21, a capacitor 22 is connected, and when the circuit 21 is made into the off condition, the voltage VAGC1 immediately before the off action is executed is held. The circuit 21 is synchronized with a selecting circuit 11, and while the circuit 11 selects a reference power source 14, the on condition is obtained. Consequently, while one side magnetic head 5A (or 5B) executes reproducing action and other magnetic head 5B (or 5A) executes recording action, namely, a reproducing video signal SV1 is muted, the voltage VAGC1 is held to the preceding voltage. Thus, the disturbance of the reproducing signal can be effectively evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a video tape recorder, and is suitable for application to, for example, an 8 mm video tape recorder (VTR).

B. Summary of the Invention The present invention provides a video tape recorder that mutes a reproduced video signal for a predetermined period during dubbing and at the same time
GC (automatic gain control)
l) By holding the voltage and maintaining the gain of the AGC circuit for the reproduced video signal at a constant value, reproduced video without disturbance can be obtained.

C. Prior Art Conventionally, in this type of VTR, as shown in FIG.
A format that forms an audio signal recording area ARA and a video signal recording area ARV is used for I, TB2, TA3, and TB4, respectively.

In such a VTR, the video signal recording area AR
Some devices have a function of recording a PCM audio signal in the audio signal recording area ARA while reproducing a video signal prerecorded in the V (hereinafter referred to as post-recording).

That is, as shown in FIG.
is a PC that receives the audio signal SA and time-compresses it.
After converting into the M audio recording signal SPCM, it is output to the selection circuit 2.

The selection circuit 2 selects a sampling pulse SWP (see FIG. 5(A)) obtained in synchronization with the rotation of a rotating drum (not shown).
) at the timing of PCM audio recording signals SPCMA and SPC to the recording amplifier circuits 3 and 4.
MI (Fig. 5 (B) and (C)) is output.

The recording amplifier circuits 3 and 4 each have their output ends connected to two magnetic heads 5A and 5B having different azimuth angles, and the magnetic heads 5A and 5B each move to the recording tracks TAI to 5B at timings synchronized with the sampling pulse SWP.
During the period of scanning the audio signal recording area ARA of TB4, the PCM audio recording signals spcMa and SPC
Mm is output to magnetic heads 5A and 5B. In this way, the PCM audio signal is recorded in the audio signal recording area ARA of each recording track TAI to TB4.

On the other hand, the magnetic heads 5A and 5B move to the recording track T.
During the period of scanning the video signal recording area AR2 of AI to TB4, the magnetic head 5A is
and reproduction output signals 5PBA and SPB obtained from 5B.
m (FIG. 5 (D) and (E)), a regenerative amplifier circuit 6 that operates during the corresponding period at the timing of the sampling pulse SWP.
and 7 to the selection circuit 10.

The selection circuit 10 alternately switches the contacts at the timing of the sampling pulse SWP, and thus reproduces output signals 5PBA and 5B obtained from the magnetic heads 5A and 5B, respectively, during the period in which the magnetic heads 5A and 5B scan the video signal recording area ARV. A reproduced video signal obtained by alternately switching the output of the 5PBI is output to the selection circuit 11.

The variable gain amplifier circuit 12 constitutes an AGC circuit for the reproduced video signal together with the AGC detection circuit 13, and after amplifying the reproduced video signal S obtained via the selection circuit 11 to a predetermined signal level, the variable gain amplifier circuit 12 is connected to the signal processing circuit (Fig. (not shown) and output to the AGC detection circuit 13.

The AGC detection circuit 13 detects an AGC voltage obtained according to the signal level of the reproduced video signal SV, and feeds it back to the variable gain amplifier circuit 12.

In this way, a reproduced video signal Sv maintained at a predetermined signal level is obtained at the output terminal of the variable gain amplifier circuit 12, and a video signal can be obtained while recording a PCM audio signal based on this reproduced video signal Sv. May perform dubbing functions.

However, in reality, in the 8 mm video format, when the magnetic tape 1 is wound around the rotating drum, the video signal recording area ARV is 18 mm on the rotating drum.
Occupies an angle range of 0°, audio signal recording area AR
A is standardized to cover an angular range of approximately 30°.

Therefore, while one magnetic head 5A (or 5B) is scanning the video signal recording area ARV, the other magnetic head 5B (or 5A) is recording the audio signal i! at Tl and T3 (or T2). A period TX occurs during which area ARA is scanned, and when performing such an after-recording operation, this period TX is
During this time, one of the magnetic heads 5A (or 5B) performs a recording operation,
A period TX occurs during which the other magnetic head 5B (or 5A) performs a reproducing operation.

However, when two magnetic heads 5A or 5B are used to perform recording and reproducing operations at the same time, the signal level of the recording signal is extremely large compared to the signal level of the reproduction signal, so crosstalk occurring in the rotary transformer, etc. Reproduction output signal 5PBA and SPB, to PC
The M audio recording signals S P CMa and SPCM begin to jump (FIGS. 5(D) and (E)).

Therefore, in a conventional VTR having an after-recording function, a selection circuit 11 is connected to the input terminal of a variable gain amplifier circuit 12, and a period during which a PCM audio recording signal SPCMa (or SPCMI) is supplied to one magnetic head 5A (or 5B). During TX, the contact of the selection circuit 11 was switched to the reference power supply 14.

With this configuration, the signal level of the reproduced video signal S can be changed by replacing the reproduced output signals 5PBA and 5pBn input to the variable gain amplifier circuit 12 with a predetermined DC voltage level (hereinafter referred to as DCW). During the period TX, the PCM audio recording signals S P CMa and SPCM can be set to "0" level (this state is called mute).

Even if the video jumps into the playback output signals SPBa and SPBm, the playback video signal S is not affected by this jump.
V can be obtained (Fig. 5 (G)).

D Problems to be Solved by the Invention However, when the reproduced output signals 5PBA and spB input to the variable gain amplifier circuit 12 are replaced with DC as shown in FIG. 5, the signal level of the reproduced video signal Sv during this period TXO changes. Since it becomes “0” level, AGC@pressure VA
GC (Figure 5 (F)) rises to an extremely large value,
The gain of the AGC circuit becomes a large value.

After the period TX has elapsed, the AGC voltage VAGC that has risen in this way is selected by the selection circuit 11 as the regenerated output signal 5.
Even if it is switched to the PBA and 5PBI sides, it cannot fall immediately, but starts to fall after a predetermined time constant.

Therefore, as the AGC voltage VAGC changes, the gain of the AGC circuit becomes larger than the predetermined level gain during this falling period, and as a result, the variable gain amplifier circuit 12
After the period TX has elapsed, the reproduced video signal Sv output from the reproducing video signal Sv suddenly rises to a large signal level and gradually changes to a predetermined signal level. (Figure 5 (F)).

If the signal level of the reproduced video signal Sv suddenly changes in this way, there is a problem in that the reproduced image is disturbed, resulting in an extremely unsightly image.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a VTR that can easily produce reproduced video images that can prevent disturbances during post-recording.

E Means for Solving the Problem In order to solve this problem, in the present invention, first and second magnetic heads 5A and 5 having different azimuth angles are used.
Each recording track TAI, TB2, TA formed by the helical scan double azimuth recording method using B
3. Audio signal recording area ARA in TB4
In the video tape recorder configured to form a video signal recording area ARV and a video signal recording area ARV, a reproduced video signal SVI obtained from the video signal recording area AR2 via the first and second magnetic heads 5A and 5B is transmitted to the AGC circuit 12. 1
At the same time, during post-recording, the audio signal S is held at a predetermined signal level through the audio signal recording area ARA using one of the magnetic heads 5A (5B) of the first and second magnetic heads 5A and 5B. PCMa
During the period TX for recording 1 (S P CM++ ), the reproduced video signal S obtained from the video signal recording area ARV
At the same time as muting VI, A of AGC circuit 12.13
The GC voltage VAGC1 is held.

During two-action post-recording, by muting the reproduced video signal SVl and simultaneously holding the AGC voltage VAGCI during the period TXO during which one of the magnetic heads 5A (5B) is recording the audio signal SPCMA (SPCM,),
After the period TX has elapsed, it is possible to effectively avoid a sudden change in the signal level of the reproduced video signal SVI when the hold of the pressure VAGC1 on AGCl is released.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. It is designed to output to . Furthermore, a capacitor 22 is connected to the output end side of the switch circuit 21, and when the switch circuit 21 is turned off, the AGC voltage VA immediately before the off operation is
It is designed to hold Gl.

The switch circuit 21 is in an on state during a period TXO during which the selection circuit 11 selects the reference power supply 14 in synchronization with the selection circuit 11 .

Therefore, during the period TX in which one magnetic head 5A (or 5B) performs a reproducing operation and the other magnetic head 5B (or 5A) performs a recording operation (that is, during the period in which the reproduced video signal SVI is muted), the AGC voltage VAGC1 will be held at the previous voltage VDC (Figure 2 (F))
.

Therefore, when the reproduced video signal Sv1 is muted, the gain of the AGC circuit does not rise to a large gain as in the conventional case, but instead holds the gain immediately before muting.

Therefore, even if muting is canceled after the period TX has elapsed, the output level of the reproduced video signal Svl does not change suddenly and is output at a substantially constant signal level.

In this way, the playback output signals 5PBA and SPB are combined with the PCM audio recording signals SPCMA and spcMl (second
(B) and (C)) jump (Fig. 2 (D) and (E)), by replacing this signal part with DC, the reproduced video signal SVI of the relevant period can be muted, and after unmuting, By preventing sudden changes in the signal level of the reproduced video signal SVI, disturbances in the reproduced video can be effectively avoided.

According to the above configuration, it is possible to not only mute the reproduced video signal (by holding the AGC voltage and maintaining the gain of the AGC circuit at a predetermined value, the signal level of the reproduced video signal SVI suddenly changes during dubbing). Since there is no change in the state, it is possible to obtain undisturbed reproduced video.

H Effects of the Invention As described above, according to the present invention, it is possible to obtain a VT that can reproduce a reproduced video in which disturbances are prevented from occurring during dubbing.
R can be easily realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the VTR according to the present invention, FIG. 2 is a signal waveform diagram for explaining its operation, and FIG.
4 is a block diagram showing a conventional VTR, and FIG. 5 is a signal waveform diagram explaining its operation. 1... PCM audio recording circuit, 2.10.11.
... Selection circuit, 3.4 ... Recording amplifier circuit, 5A, 5B ... Magnetic head, 6.7 ...
...Regenerative amplifier circuit, 12...Variable gain amplifier circuit, 13...AGC detection circuit, 14...
Reference power supply, 21...Switch circuit, 22...
...Capacitor.

Claims (1)

[Scope of Claims] An audio signal recording area and a video signal recording area are respectively formed in each recording track formed by a helical scan double azimuth recording method using first and second magnetic heads having different azimuth angles. In the video tape recorder, a reproduced video signal obtained from the video signal recording area via the first and second magnetic heads is held at a predetermined signal level via an AGC circuit, and during post-recording, , during a period of recording an audio signal in the audio signal recording area using one of the first and second magnetic heads, muting the reproduced video signal obtained from the video signal recording area and simultaneously A video tape recorder characterized in that the AGC voltage of the AGC circuit is held.