JPS6141285A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a sharp screen free from noises by using a noise reduction means which separates the high band component of a flat part of the reproduction video signal modulated from a recording medium and subtracting or adding the reproduction video signal and a control means which detects the noise amount within a vertical blanking time of the reproduction video signal and controls the noise reduction means. CONSTITUTION:A luminance signal (a) is branched into three parts and sent to a high-pass amplifier 16, a low-pass amplifier 17 and a noise amount detector 20 in the form of waveforms (b), (d) and (f) respectively. The noises of a flat part of a video signal that affect easily a screen differ according to the signal contents recorded on a tape. Therefore the clipping level of a diode clipper 21 is varied within a prescribed range between MIN and MAX and controlled by the output voltage (f) of the detector 20. Thus a signal having a waveform (g) is produced. Both figures (1) and (2) in the figure (g) show the MAX and MIN clipping levels respectively. Waveforms (g) and (d) are mixed by a MIXAMP19 for production of a screen of a waveform (h) which is free from noises.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording/reproducing apparatus having a noise reduction function for video signals reproduced from a tape.

Conventional configuration and its problems Since the signal reproduced from the tape contains high-frequency FM noise, many magnetic recording and reproducing apparatuses perform the following noise reduction. In other words, noise in flat areas of the video signal, that is, on a flat screen, is visually noticeable, but such areas do not contain much high-frequency components, so if there are minute high-frequency components, they should be treated as noise. is being removed.

A conventional magnetic recording/reproducing device will be explained below. 1st
The figure shows the basic configuration of the luminance signal reproducing system of a conventional magnetic recording and reproducing device. (1) is a video head, (2) is a reproduction amplifier, (3) is a switcher 1, and (4) is a switching signal. The input terminal (5) is a high-pass filter (rHPFJ
), (6) is a dropout compensation circuit (rD
(7) is a limiter (hereinafter referred to as rLIM)
J), (8) is an FM demodulator, (9) is an equalizer (hereinafter referred to as rEQJ), (10) is a de-emphasis circuit, (11) is a non-linear de-emphasis circuit,
(12) is a low-pass filter (hereinafter referred to as "LPFJ"),
(13) is a noise canceller circuit, (14) is an output circuit, and (15) is a color signal input terminal.

The low carrier FM signals alternately reproduced by the rotating video heads (1) of the first and second channels are amplified by the reproduction amplifiers (2) of the respective systems, and then sent to the switcher (3).
is supplied to In this switcher (3), 307 flip-flop signals synchronized with the rotating video λtud (1) are supplied from the servo circuit to the switching signal input terminal (4), and a switching operation is performed thereby. 1
and the two systems of signals of the second channel are made into one continuous signal. Since this reproduced signal includes a low-frequency converted color signal, it is branched into two parts, one of which is supplied to the color signal reproduction circuit, and the other of which is supplied to the HPF (5) of the luminance signal reproduction circuit.
). HP F (5) removes the low frequency converted color signal from the reproduced signal. Glue after HPF (5).

C(6) functions to replace dropouts caused by scratches on the tape, uneven magnetic powder, etc. with the FM signal of one horizontal period earlier by using the line correlation of the video signal.

The FM signal whose dropout has been corrected by the DOC (6) is supplied to the LIM (7), which removes level fluctuations included in the reproduced FM signal. The FM wave whose amplitude has become completely constant in the LIM (7) is converted to F by the FM demodulator (8).
The M signal is returned to the luminance signal. Then, in EQ (9), the luminance signal is delayed to match the timing with the color signal of the reproduced output. Next, the luminance signal passes through a de-emphasis circuit (10) and a non-linear de-emphasis circuit (11), which have characteristics opposite to the pre-emphasis and non-linear emphasis during recording, to reduce noise components in the middle and high ranges. The next stage L P F (12) is F
Eliminate leakage of the FM carrier and its second harmonic from the M demodulator (8). Finally, the noise canceller circuit (
After noise components in the luminance signal are reduced in step 13), the color signals from the color signal input terminal (15) are mixed to form a complete video signal and supplied to the output circuit (14).

FIG. 2 shows the configuration of a noise canceller circuit (13), which constitutes a blocking type noise reduction circuit that uses the cutoff region of a diode to block the passage of noise components. The luminance signal (Fig. 3(a)) from the LPF (12) is branched into two and sent to a bypass amplifier (16) and a low-pass amplifier (17).
The waveforms are as shown in FIGS. 3(b) and 3(d), respectively. The noise in the flat part of the video signal, which tends to affect the screen, is concentrated in the low level of the signal that has passed through the bypass amplifier (16), so the diode clipper (I8) removes this noise, and ) to create a waveform signal like this. Third
The signals with the waveforms shown in Figures (c) and (d) are generated by a mixing amplifier (r
The signals are mixed in step (19) (denoted as M I

However, in the conventional configuration as described above, the output of the bypass amplifier (16) contains high-frequency components of the video signal, and the high-frequency components of the screen are lost depending on the output level setting of the diode clipper (18). This method also has the disadvantage that noise with a high level cannot be removed.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide a magnetic recording and reproducing device that can remove noise on the screen and obtain a faithful screen without noise.

Structure of the Invention In order to achieve the above object, the magnetic recording and reproducing apparatus of the present invention includes noise reduction means for separating the high frequency component of the flat part of the reproduced video signal demodulated from the recording medium and subtracting or adding it from the reproduced video signal. Then, the amount of noise during the vertical blanking period of the reproduced video signal is detected, and the amount of high frequency components in the flat part of the reproduced video signal to be subtracted or added from the reproduced video signal is increased or decreased in accordance with the increase or decrease in the noise amount. and a control means for controlling the noise reduction means.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 4 is a circuit block diagram of a noise reduction circuit of a magnetic recording/reproducing apparatus according to an embodiment of the present invention, in which the same components as those shown in FIG. do. The luminance signal (a) is branched into three parts and sent to a bypass amplifier (16), a low-pass amplifier (17), and a noise amount detector (20), each having a waveform (b) (
d) It becomes like (f). The noise in the flat parts of the video signal that tends to affect the screen also differs depending on the signal content recorded on the tape. Therefore, the clipper level of the diode clipper (21) is made variable within a predetermined range from MIN to MAX, and is controlled by the output voltage (f') of the noise amount detector (20) to create a signal like the waveform (g). do. In Figure 5 (g), (a) is when the clipper level is MAX, and (b) is when the clipper level is MT.
This is the case of N. Waveform (g) and waveform (d) are M T
The images are mixed using XAMP (19) to create a noise-free screen like the waveform (h). In addition, in Fig. 5 (11), (
(a) is the case when the clipper level is MAX, and (b) is the case when the clipper level is MIN.

Next, the means for creating the waveform (f) will be explained in detail. The waveform (f) detects the amount of noise in the reproduced video signal and is output as a voltage displacement corresponding to the amount of noise, and this voltage changes the clipper level of the diode clipper (21). Figure 4 shows a noise amount detector (20
), in which (22) is a noise detector, (2
3) is a first monostable multivibrator (hereinafter referred to as "first MMJ"), (24) is a second monostable multivibrator (hereinafter referred to as "second MMJ")
, (25) is a detector, and (26) is a voltage converter. FIG. 7(a) is an enlarged waveform of the vertical blanking period portion of the reproduced video signal, and FIG. 7(i) is a 3011z flip-flop signal synchronized with the rotating video head from the servo circuit.
It is located 5 to 6 horizontal frequencies before the vertical equalization pulse of the reproduced video signal. (j) is a pulse that becomes high level or low level only during the vertical blanking period. The noise detector (22) is configured to operate only when the output (j) of the second M M (24) is at a high level °. The reproduced video signal during the vertical blanking period (a
) does not include a video signal, only a synchronization signal. Therefore, noise in the reproduced signal that is not affected by the video signal can be extracted by the noise detector (22). Noise from the noise detector (22) is detected by a wave detector (25) and converted to a voltage as shown in FIG. 5(f) by a voltage converter (26).

According to this embodiment, it is possible to detect the noise level during the vertical blanking period of the reproduced video signal and automatically change the mixing level of the high frequency components of the video signal in accordance with the noise level. , can provide a noise-free screen.

In this embodiment, an example in which high-frequency components are added is explained, but the same effect can be obtained by subtracting them.

As described in detail, according to the present invention, the mixing level of the high-frequency components of the reproduced video signal is automatically changed according to the noise level in the reproduced video signal, so that clear noise-free images can be obtained. You can get a screen like this.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of a conventional magnetic recording and reproducing device, FIG. 2 is a circuit block diagram of a noise reduction circuit of the same magnetic recording and reproducing device, and FIG. 3 is a signal waveform diagram of each part of the circuit shown in FIG. 2.
FIG. 4 is a circuit block diagram of a noise reduction circuit of a magnetic recording/reproducing apparatus according to an embodiment of the present invention, FIG. 5 is a signal waveform diagram of each part of the circuit shown in FIG. 4, and FIG. A circuit block diagram of the noise amount detector included in the mitigation circuit,
FIG. 7 is a signal waveform diagram of each part of the circuit shown in FIG. 6. (16)...Bypass amplifier, (17)...Low pass amplifier, (19)...Mixing amplifier, (20)...
Noise amount detector, (22)... Noise detector, (23
) (24)... Monostable multivibrator, (25)... Detector, (26)... Voltage converter agent Yoshihiro Morimoto Figure 3 (b) 5-, G Figure 4 Figure 5 II Figure 5

Claims (1)

[Claims] 1. A noise reduction means that separates the high frequency component of the flat part of the reproduced video signal demodulated from the recording medium and subtracts or adds it from the reproduced video signal, and detects the amount of noise during the vertical blanking period of the reproduced video signal. and a control means for controlling the noise reduction means to increase or decrease the amount of high-frequency components in the flat part of the reproduced video signal to be subtracted from or added to the reproduced video signal in response to an increase or decrease in the amount of noise. Device.