JPH0684280A - Noise reducing circuit - Google Patents

Abstract

PURPOSE:To improve the balance of S/N and resolution by varing the noise reducing amount of the high-frequency components of reproduced video signals corresponding to the detected output level of reproduced modulation signals. CONSTITUTION:In a VTR, reproduced signals 10a from a head tape system are inputted through an AGC 11 and an FM demodulation circuit 12 to a noise reducing circuit A as video signals aa, a noise reducing processing is performed and the video signals bb are outputted. At this time, the reproduced signals 10a are detected at a detection circuit 13, the coefficient K2 of a coefficient unit 6 is variably controlled by output signals 13a corresponding to the levels and the noise reducing amount is set corresponding to the level of the video signals aa. Thus, by varing the noise reducing amount corresponding to the level of the reproduced signals, the S/N and the resolution of output video signals can be well balanced. Also, a similar effect can be obtained even by supplying control signals 13a to the coefficient unit 3 and variably controlling the coefficient K1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction circuit suitable for a magnetic recording / reproducing apparatus (hereinafter abbreviated as "VTR").

[0002]

2. Description of the Related Art As a noise reduction circuit suitable for a VTR, the applicant previously proposed JP-A-63-18811. Since the present application is an invention related to this improvement, this will be described as a conventional technique. FIG. 3 is a block diagram of a conventional noise reduction circuit.
FIG. 4 is a waveform diagram for explaining the signals of FIG.

In FIG. 3, the video signal aa shown in FIG. 4A is supplied to the high-pass filter 1, and the signal obtained by extracting a relatively high frequency component is amplitude-limited by the limiter 2 and the same. The limiter output signal 2a shown in FIG. Then, the limiter output signal 2a is supplied to one input of the subtractor 4 via the first coefficient unit 3 having the coefficient k1, and is subtracted from the video signal aa supplied to the other input, as shown in FIG. The subtractor output signal 4a shown in C) is obtained. The subtractor output signal 4a becomes the delay signal 5a shown in FIG. 3D via the delay circuit 5 having a delay time of Δτ, and is supplied to one input of the adder 7. Further, the other input of the adder 7 is supplied with the signal obtained by the limiter output signal 2a via the second coefficient unit 6 having the coefficient k2, and the both are added and added (E). The output video signal bb shown in FIG.

As described above, in the conventional noise reduction circuit, the limiter output signal 2a which is a high frequency component and a small amplitude component of the video signal aa is regarded as noise and the video signal a is considered.
The S / N of a was improved.

[0005]

In the noise reduction circuit described above, high frequency components and small amplitude components are regarded as noise. Therefore, if the noise reduction amount is large, the high frequency components in the video signal aa are lost and the resolution is reduced. It will cause deterioration. Therefore, the noise reduction amount is determined by the balance between S / N and resolution.

Assuming that a conventional noise reduction circuit is applied to a VTR, the reproduction level is lowered due to the influence of reproduction demagnetization as the number of reproduction times of the magnetic tape increases, so that S / of the video signal aa is reduced. N deteriorates. Further, when the high performance magnetic tape is used, the S / N of the video signal aa is improved. Thus, the S / N of the video signal aa which is the input signal of the noise reduction circuit fluctuates. Therefore, it is desirable that the noise reduction amount of the noise reduction circuit is originally variable according to the S / N of the video signal aa.

However, in the conventional noise reduction circuit, the coefficients k1 and k2 of the first and second coefficient multipliers that determine the noise reduction amount are fixed, so that the S / N ratio of the video signal aa is changed. The amount of noise reduction could not be changed, and the balance between S / N and resolution was poor.

Therefore, an object of the present invention is to provide a noise reduction circuit that solves the above problems.

[0009]

The present invention provides the following configurations in order to solve the above problems.

A noise reduction circuit for automatically reducing the noise of a reproduced video signal obtained by performing FM demodulation after automatically adjusting the level of the FM-modulated reproduced modulation signal, which is a small-amplitude high-frequency component of the reproduced video signal. Extracting means for outputting the extracted signal obtained by extracting the detected signal, detecting means for outputting the detected signal obtained by detecting the level of the reproduction modulation signal, the extracted signal variable according to the detected signal, and A noise reduction circuit comprising: an arithmetic processing unit that arithmetically processes a reproduced video signal, and varying a noise reduction amount of a high frequency component of the reproduced video signal according to the detected signal.

[0011]

1 is a block diagram for explaining a main part of an embodiment in which a noise reduction circuit according to the present invention is applied to a VTR, and FIG. 2 is a waveform diagram for explaining the signals of FIG.
Embodiments will be described below with reference to the drawings. The same components as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, a recording signal FM-modulated at the time of recording is reproduced from a head tape system (not shown) and supplied to a preamplifier 10, where a reproduction signal 10a obtained by performing predetermined amplification is automatically gain adjusted. A circuit (hereinafter abbreviated as “AGC”) 11 and first, second and third detection circuits 13, 14,
15 and supply. The third detection circuit 15 is for detecting the level of the reproduction signal 10a to obtain a third control signal used for auto-tracking, and based on this signal, the rotary magnetic head and the reproduction track during reproduction. The servo system 16 controls the phase between and.

The above-mentioned AGC 11 is for keeping the input level of the FM demodulation circuit 12 at the subsequent stage at a predetermined level, and the second control circuit 14 detects the level of the reproduced signal 10a to obtain a second control signal. Based on this, the level of the reproduction signal 10a which depends on the reproduction demagnetization or the performance of the magnetic tape is amplified to a predetermined level.

The output signal of the AGC 11 is supplied to the FM demodulation circuit 12, where FM demodulation is performed and de-emphasis, which is complementary to pre-emphasis performed at the time of recording, is applied to obtain a video signal aa. ing.

The video signal aa is supplied to the noise reduction circuit A and subjected to noise reduction processing to obtain an output video signal bb with improved S / N. Here, the noise reduction circuit A differs from the conventional one in that the coefficient k of the second coefficient unit 6 is
2 is variably controlled using a control signal 13a described later, and the noise reduction amount is set according to the S / N of the video signal aa.

That is, since it is determined by the level of the signal reproduced by the magnetic head (not shown) and supplied to the preamplifier 10, the S of the video signal aa is set to the level of the reproduced signal 10a obtained by amplifying this signal with a constant amplification factor. / N depends.
Therefore, the reproduction signal 10a is level-detected by the first detection circuit 13, and the first control signal 13a corresponding to the level is detected.
Is supplied to the second coefficient unit 6.

Now, since the level of the reproduced signal 10a is high and the S / N of the video signal aa is good, on the contrary, the level of the reproduced signal 10a is low, the S / N of the video signal aa is bad. To explain by comparing with the case, FIG.
(A) to (E) correspond to the former, and (F) to (J) of the same figure correspond to the latter.

FIGS. 3A, 3F and 3B,
As shown in (G), the S / N of the video signal aa is good or bad depending on the level of the reproduced signal 10a. Then, as shown in (C) and (H) of FIG.
The noise superimposed on a is larger in FIG. 6H where the level of the reproduced signal 10a is smaller. Therefore, the second coefficient output signal 6a also becomes larger in the figure (I) than in the figure (D). The output video signal bb is shown in (E) and (J) of FIG.
The S / N ratios are substantially the same as shown in FIG.

In this way, since the noise reduction amount is made variable according to the level of the reproduced signal 10a, the output video signal bb has the S / N and the resolution even if the S / N of the video signal aa changes. Can be balanced.

In the above embodiment, the control signal 1
3a was supplied to the second coefficient unit 6, but since this is for varying the noise reduction amount, the first coefficient unit 3
May be supplied to the limiter 2 to variably control the coefficient k1, or to the limiter 2 to variably control the limiter level. Further, it goes without saying that a third coefficient unit may be newly inserted in the path from the output of the FM demodulation circuit 12 to the input of the limiter 2 and the coefficient may be variably controlled by the control signal 13a.

In the above-mentioned embodiment, the first, second and third detection circuits 13, 14 and 15 are provided independently, but any two or all of them may be used together. Of course, it is also good.

[0022]

As described above, according to the configuration of the present invention,
Since it has a noise reduction circuit that performs noise reduction processing on the reproduced video signal with the noise reduction amount based on the detected signal, it is possible to perform noise reduction processing according to the S / N of the reproduced video signal, and the S / N of the output video signal. And there is an effect that the balance of resolution can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining a main part of an embodiment in which a noise reduction circuit according to the present invention is applied to a VTR,

FIG. 2 is a waveform diagram for explaining the signals of FIG.

FIG. 3 is a block diagram of a conventional noise reduction circuit.

FIG. 4 is a waveform diagram for explaining the signals of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High-pass filter (extracting means) 2 Limiter (extracting means) 13 First detection circuit (detection means) 10a Reproduction signal (reproduction modulation signal) aa Video signal (reproduction video signal) bb Output video signal A Noise reduction circuit

Claims (1)

[Claims] 1. A noise reduction circuit for automatically reducing the noise of a reproduced video signal obtained by FM demodulating after automatically adjusting the level of an FM-modulated reproduced modulation signal, the high-frequency band having a small amplitude in the reproduced video signal. Extraction means for outputting an extraction signal obtained by extracting a frequency component, detection means for outputting a detection signal obtained by detecting the level of the reproduction modulation signal, and the extraction signal variable according to the detection signal A noise reduction circuit comprising: an arithmetic processing unit that arithmetically processes the reproduced video signal; and varying a noise reduction amount of a high frequency component of the reproduced video signal according to the detected signal.