JPH05161111A - Video and audio signal processing circuit - Google Patents

Abstract

PURPOSE:To obtain a stable after-recording pattern while flicker or skew is suppressed especially with respect to a circuit applying post recording to an overlapped part in a VTR adopting the overlap system. CONSTITUTION:A missing part of a video signal of a PCM audio signal due to crosstalk generated for each field is replaced with an other video signal by a usual luminance signal processing circuit 7 and a usual chroma signal processing circuit 17 and a missing part of a video signal due to crosstalk of a blanking signal generated once for each of two fields is replaced with a video signal of one preceding field by post-stage fields NR26, 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a video signal and a PC, for example.
The present invention relates to a magnetic recording / reproducing device (hereinafter abbreviated as VTR) for overlapping recording with an M audio signal, and particularly to an audio and video signal processing circuit capable of after-recording (hereinafter abbreviated as abbreviated).

[0002]

2. Description of the Related Art A so-called overlap type V having at least two rotating magnetic heads and having a period in which the two rotating magnetic heads simultaneously contact a magnetic tape is adopted.
In TR, after-recording can be performed during this period.

FIG. 6 shows an example of the positions of the magnetic head and the magnetic tape on the rotary cylinder in the 8 mm video standard VTR adopting the overlap system. A few
Is a rotary magnetic head, 4 is a rotary erasing head, 101 is a magnetic tape, 102 is a rotary cylinder, and 103 and 104 are tape guides.

With the 8 mm video, three modes of 8-bit mode, 12-bit mode and 16-bit mode can be selected for the PCM audio signal. In the case of an 8-bit PCM audio signal, a magnetic tape is wound around a 216-degree rotating cylinder, the breakdown of which is a time-compressed PCM audio signal of 36 degrees and a video signal of 180 degrees. For 12-bit and 16-bit PCM audio signals, the tape winding angle is 221 degrees and the PCM audio signal portion is 41 degrees.
It is degree.

FIG. 7 is a diagram showing a tape pattern on a magnetic tape in the case of an 8-bit PCM audio signal. Reference numeral 101 is a magnetic tape, and 105, 106 and 107 are recorded tracks. The 36-degree section at the bottom of the tape with diagonal lines is
This is a portion in which a PCM audio signal and a tracking pilot signal necessary for reproduction are multiplexed and recorded. Besides 1
The 80 degree section is a portion in which a video signal and the pilot signal are multiplexed and recorded.

For example, in the 8 mm video having the head arrangement shown in FIG. 6, when the PCM audio signal is post-recorded, the PCM audio signal mainly cross-talks with the reproduced video signal in the rotary cinder and the reproduced video signal deteriorates. ..

In Japanese Patent Publication No. 41952/1990, deterioration of the reproduced video signal is reduced by replacing the reproduced signal with another video signal synchronized with the reproduced signal during the period when the PCM audio signal crosstalks with the reproduced video signal. ..

[0008]

In the 8 mm video, the reproduction tracking pilot signal is recorded while being superimposed on the PCM audio signal and the video signal. The recorded signal on the magnetic tape can be updated by overwriting the PCM audio signal, but since the pilot signal is a low frequency signal having a frequency of about 100 kHz to about 150 kHz, old recording will remain if it is overwritten. Therefore, in order to completely erase the pilot signal of the PCM audio signal portion, erasing may be performed in advance by the rotary erasing head.
Generally, one rotation erasing head is used for cost reduction,
It has a track width and can erase two tracks simultaneously by one scan.

As in the case of the recorded PCM audio signal, the erase signal mainly cross-talks with the reproduced video signal in the rotary cininder. This situation will be described with reference to FIG. FIG. 4A is a diagram schematically showing the signals reproduced by the rotary magnetic heads 2 and 3 when the head arrangement shown in FIG. In the figure, P indicates a PCM audio signal and Vi indicates a video signal. FIG. 4 (2) is a signal for switching the rotary magnetic heads 2 and 3, and FIG. 4 (3) is a signal indicating the position of the PCM audio signal on the time axis in the reproduction signal, which has a width t1. In the configuration of FIG. 6, since the rotary erasing head 4 precedes the magnetic head 2 by 90 degrees, erasing is performed by 90 degrees prior to the period in which the magnetic head 103 reproduces the PCM audio signal portion. The width of the erasing period is t1 described above or t2 in which the trailing edge is cut to be narrow. The reason for narrowing the width is to provide a margin so that the video signal portion is not accidentally erased due to the mounting accuracy of the magnetic head or the erasing head.

FIG. 4 (5) shows the output of the reproducing amplifier. Of the reproduced signal, the PCM audio signal period becomes noise-like and the erase signal becomes a crosstalk signal during the erase period.

Generally, the erase signal supplied to the rotary erase head 4 is a single signal having a frequency of about 8 MHz. In 8mm video, the luminance signal is in so-called low-band mode, 4.2MHz at the sync tip and 5.4MH at 100% white.
z, high band mode, sync tip 5.7MHz, 10
0% white is frequency-modulated to 7.7 MHz. Therefore, when the erase signal cross-talked with the reproduced video signal is demodulated, the white level exceeds 100%.

FIG. 4 (6) shows the luminance signal output. the above,
PC by the technology disclosed in Japanese Patent Publication No. 2-41952
The M audio signal period can be replaced with a black signal with a sync signal. However, the erase signal period is as described above.
There is no sync signal and the white level exceeds 100%.

FIG. 5 shows the case where such a reproduction signal is displayed on the monitor. Since the crosstalk of the erase signal occurs once in two fields, as shown in FIG. 5A, the (n-1) th field where the lower part of the screen is only black and the lower part of the screen is black and the center of the screen is white. And the n-th field appearing alternately on the monitor. Further, in the n-th field, since the synchronizing signal is not reproduced during the crosstalk period of the erase signal, the horizontal AFC of the monitor is free-running, and the skew occurs immediately after the end of the crosstalk period.

Therefore, on the actual screen, as shown in FIG. 5B, a flicker occurs in the center, and it seems that a normal reproduction signal and a reproduction signal in which skew has occurred overlap directly below the flicker.

As described above, when erasing is performed by the rotary erasing head during PCM dubbing, flicker and skew are generated on the screen, which is unsightly. However, the above-mentioned prior art does not mention erasing by the rotary erasing head.

It is an object of the present invention to reduce the deterioration of the reproduced video signal when erasing by the rotating erasing head to post-record the overlap period, and to obtain a stable reproduced screen.

[0017]

As described above, since crosstalk of the erase signal occurs once in two fields, there is no crosstalk during the period when the crosstalk occurs.
Replace with the video signal of the same period before the field. For example, with the field memory, the video signal of one field before can be easily used.

[0018]

In the present invention, paying attention to the fact that the correlation between the fields of the video signal is relatively high, the video signal of the same period one field before the crosstalk of the erase signal occurs during the period when the crosstalk of the erase signal occurs. By replacing with
It is possible to prevent flicker without loss of video signals.

Further, by replacing the period in which the video signal is lost with the video signal of one field before, the horizontal synchronizing signal is always continuous, so that the horizontal AFC of the monitor is stable and the occurrence of skew can be prevented.

[0020]

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 video and audio signal processing circuit according to the present invention, in which 1 is a magnetic tape, 2 is a magnetic head, 3 is a rotational erasing head, and 5 is recording / reproducing. An amplifier, 6 is a drive circuit for the rotation erasing head, 7 is a luminance signal processing circuit, 8 is a peaking circuit, 9 is a limiter circuit, 10 is a frequency demodulation circuit, 11 is a de-emphasis circuit, 12 is a mute circuit, and 13 is 1H (H. (Horizontal sync signal period) delay circuit, 14 dropout compensation circuit, 15 line noise canceller, 16 horizontal / vertical sync signal insertion circuit, 17 chroma signal processing circuit, 18
Is LPF, 19 is ACC (Automatic Chr.
oma level control circuit, 20 is a reproduction frequency conversion circuit, 21 is a chroma comb filter, 22 is a 1H delay circuit, 23 is a burst / chroma de-emphasis circuit, 24 is a chroma killer circuit, 25 is a mute circuit, 26 is a luminance field noise reducer. (Hereinafter abbreviated as field NR), 27 is an A / D conversion circuit, 28 is a field memory, 29 is a noise reducer (hereinafter abbreviated as NR), 30 is a D / A conversion circuit, 31 is a switch, 32
Is a chroma field NR, 33 is an A / D conversion circuit, 34
Is a demodulation circuit, 35 and 36 are NR, 37 and 38 are field memories, 39 is a modulation circuit, 40 is a D / A conversion circuit, 4
Reference numerals 1 and 42 are switches, 43 is a reproduction FM audio signal processing circuit, 44 is a PCM audio signal processing circuit, 45 is an audio switching circuit, and 46 is a field NR dubbing control signal.

The input voice signal is a voice signal switching circuit 45.
After that, the PCM audio signal processing circuit 44 modulates the time-axis compressed PCM audio signal and supplies it to the recording / reproducing amplifier 5. The recording / reproducing amplifier 5 records the PCM audio signal on the magnetic tape 1 via the magnetic heads 2 and 3 based on the head switching signal and the PCM gate.

The video signal is read from the magnetic tape 1 via the magnetic heads 2 and 3, and is amplified by the recording / reproducing amplifier 5. The state of video signal processing will be described with reference to FIG.

FIG. 2A is a diagram schematically showing a PCM audio signal and a video signal recorded / reproduced by two magnetic heads with their time axes aligned. In the figure, P indicates a PCM audio signal and Vi indicates a video signal. 2 (2) is a signal for switching between two magnetic heads, and FIG. 2 (3) is a PC to be recorded.
The signal indicates the position of the M audio signal and has a width of t1.

As shown in FIG. 6, since the rotation erasing head 4 leads the CH1 head 2 by 90 degrees,
As shown in (4), the CH1 head 2 supplies an erasing signal to the rotation erasing head 4 90 degrees before the PCM audio signal is recorded. The erase signal width is t1 which is the same as that of the PCM audio signal or t2 in which the margin is taken into consideration by trimming the trailing edge so that the video signal is not erased by mistake and the margin is taken into consideration. Also, the erase signal frequency is generally about 8 MHz.

The output of the recording / reproducing amplifier 5 is shown in FIG. The PCM audio signal and the erase signal cross-talk with the reproduced signal. Since both are large-amplitude signals, the preamplifier is saturated, and small-amplitude reproduced signals disappear. In particular, since the PCM voice signal is a digital signal, it becomes noise-like.

The output of the recording / reproducing amplifier 5 is supplied to the peaking circuit 8, the LPF 18, and the reproducing FM audio signal processing circuit 43. Since the reproduced FM audio signal is an intermittent signal so that it can be easily estimated from FIG. 2 (5), the reproduced signal processing is generally not performed in many cases. Even if it is performed, the input voice signal is selected by the switching circuit 45 in order to monitor the voice signal to be recorded in the voice signal output.

The LPF 18 and below are well-known chroma signal processing circuits. The low-frequency conversion chroma signal is extracted from the video signal input to the LPF 18, the amplitude thereof is adjusted by the ACC circuit 19, and the original carrier chroma signal frequency is converted by the frequency conversion circuit 20. Further, the comb filter 21 removes crosstalk interference from the adjacent tracks included in the reproduction signal, and the burst / chroma deemphasis circuit 23,
The killer circuit 24 is input to the mute circuit 25. The mute circuit 25 mutes the period in which the PCM audio signal crosstalks according to the mute control signal CMUTE. The mute control signal CMUTE is the same as that of the PCM gate (FIG. 2 (3)), or is a signal widened before and after in order to start and cancel the mute period within the horizontal synchronization blanking period.

The peaking circuit 18 and below are known luminance signal processing circuits. The peaking circuit 18 extracts the FM luminance signal from the output of the recording / reproducing amplifier 5, phase equalizes it, and the limiter 9 and the frequency demodulation circuit 10 demodulate it to the luminance signal shown in FIG. The output of the demodulation circuit 10 passes through the main de-emphasis circuit 11 and is muted by the mute circuit 12 during the period when the PCM audio signal crosstalks, like the chroma signal. After that, dropout compensation circuit 1
4 and the line noise canceller 15, and is input to the synchronous insertion circuit 16.

The sync insertion circuit 16 inserts the horizontal sync signal and the vertical sync signal, which are missing during the PCM audio signal period, to obtain the signal shown in FIG.

The output of the sync insertion circuit 16 is converted into a digital signal by the A / D conversion circuit 27, and noise reduction utilizing the well-known field correlation is performed by the NR circuit 29.
It is supplied to the N-side terminal of the switch 31. 1 from the field memory to the other terminal of the switch 31, the AF terminal
A field delayed signal is provided. For ease of understanding, it is converted into an analog signal and shown in FIG. The switch 31 selects the N-side terminal when the AFCONT 46 (FIG. 2 (7)) is at the low level and selects the AF-side terminal when the level is at the high level to compensate for the loss of the video signal caused by the crosstalk of the erase signal. After that, the D / A conversion circuit 30
The luminance signal (10 in FIG. 2) converted into analog is obtained. Obviously, when the switch 31 selects the AF side terminal, noise reduction by the field NR cannot be performed.

Similarly to the luminance signal, the chroma signal output from the mute circuit 25 is also subjected to noise reduction by the field NR32. After being converted into a digital signal by the A / D conversion circuit 33,
The demodulation circuit 34 demodulates the BY color difference signal and the RY color difference signal. Noise is reduced by the NR 35 for the BY color difference signal and NR 36 for the RY color difference signal, and they are supplied to the N-side terminals of the switches 41, 42, respectively. Switch 41,
The operation of 42 is the same as that of the switch 31. The outputs of the switches 41 and 42 are quadrature two-phase modulated by the modulation circuit 39,
The D / A conversion circuit 40 converts the analog signal.

Here, the effect on the screen will be described with reference to FIG. FIG. 3A shows the output of the synchronous insertion circuit 16 of FIG.
It is the figure which assumed the state projected on the screen. A field in which the center of the screen becomes white appears every field. In reality, skew occurs immediately after the whitened portion. In the luminance signal output, since the loss of the video signal due to the erase signal is compensated, the normal screen is displayed in each field.

As described above, the video and audio signal processing circuit capable of post-recording for updating the tracking pilot signal in the overlap period can be realized with a simple structure in which a switch is added to the field NR circuit.

In this embodiment, the circuit having the field memory in each of the luminance signal processing step and the chroma signal processing step has been described, but any circuit having a field memory may be used, for example, a trick play memory. And TBC (Time Base Corr)
vector).

In the sync insertion circuit of FIG. 1, a horizontal sync signal may be added to the erase signal portion, but this is not effective because it is replaced with another video signal in the subsequent stage.

In this embodiment, only the erase signal portion is 1
The signal before the field was replaced. Therefore, in a video with a lot of movement, that is, a video in which the content changes for each field, an afterimage is generated only in the replaced portion, but the image quality improving effect is large compared to flicker. In order to eliminate this afterimage, although the vertical resolution is lowered, not only the erase signal portion but the entire field may be replaced with the signal one field before.

[0038]

As described above, according to the present invention,
For example, in an 8 mm video that employs the overlap method, it is possible to suppress flicker and skew that occur at the center of the screen when after-recording the overlap portion. Therefore, the operator of the VTR can post-record while monitoring the stable screen.

The present invention can be implemented by simply adding a simple circuit to the existing circuit configuration, and has an advantage that the increase in circuit scale and the increase in cost are extremely small.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a signal waveform of each part of FIG.

FIG. 3 is a diagram showing an effect on a screen according to the present invention.

FIG. 4 is a diagram showing a video signal waveform in a conventional configuration.

FIG. 5 is a diagram showing a screen in a conventional configuration.

FIG. 6 is a diagram showing a head arrangement on a rotating cylinder and a position of a magnetic tape.

FIG. 7 is a diagram showing a recording pattern on a tape of a VTR adopting an overlap method.

[Explanation of symbols]

 4 ... Rotation erasing head, 28, 35, 38 ... Field memory, 31, 41, 42 ... Switch.

Claims (3)

[Claims] 1. At least two rotating magnetic heads and one rotating erasing head having a width of two tracks,
A magnetic tape is wound around a rotating cylinder by 180 degrees or more, and has a first period in which the magnetic tape and the two rotating magnetic heads are in contact with each other at the same time. The luminance signal of the color video signal is frequency-modulated to In the video and audio signal processing circuit of the helical scan type magnetic recording / reproducing apparatus, the signal is frequency-converted to the low frequency side of the frequency-modulated luminance signal, and both are frequency-multiplexed and recorded and reproduced. When one of the tracks reproduces a track already recorded on the magnetic tape and the other magnetic head records another signal in the first period, the first period of recording or the first period of recording Means for erasing a second period narrower before and after the period before the recording by the rotary erasing head, and means for replacing the reproduction signal with the reproduction signal one field before. Means for replacing the reproduction signal with another video signal synchronized with the reproduction signal during a third period, which is wide before or after the first period, and a video and audio signal processing circuit. .. 2. A video and audio signal processing circuit according to claim 1, wherein the period for replacing the reproduced signal with the reproduced signal one field before is a period substantially equal to the period for performing the erasing. 3. A video and audio signal processing circuit according to claim 1, wherein the period for replacing the reproduction signal with the reproduction signal of one field before is the entire field in which the erasing is performed.