JPH02792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise reduction circuit, in which the frequency characteristics of a de-emphasis circuit and a pre-emphasis circuit are set such that the amount of level attenuation and the amount of level enhancement are large in a specific frequency band compared to other bands, It is an object of the present invention to provide a noise reduction circuit that can reliably suppress large amplitude noise exceeding a limiter level at a specific frequency.

FIG. 1 shows a block diagram of the recording system and playback system of a general home VTR. In the figure, during recording, a video signal input to input terminal 1 is separated into a luminance signal and a chromaticity signal in a separation circuit 2,
The luminance signal is high-frequency enhanced in the pre-emphasis circuit 3, then FM modulated in the FM modulator 4 and supplied to the mixer 5, while the chromaticity signal is processed in the color processing circuit 6 and sent to the mixer 5. The signal is mixed with a luminance signal, and is supplied to a video head 8 via a recording amplifier 7, where it is recorded on a magnetic tape 9.

On the other hand, during reproduction, the signal reproduced by the video head 8 is supplied to the separation circuit 11 via the reproduction preamplifier 10, where it is separated into a luminance signal and a chromaticity signal, and the chromaticity signal is transmitted to the reproduction color processing circuit 11.
2, the luminance signal is processed and supplied to the mixer 13, while the luminance signal is supplied to the noise reduction circuit 14, where noise components are suppressed, and then high-frequency attenuated in the de-emphasis circuit 15, and then sent to the mixer 13. 13, mixed with the chromaticity signal, and taken out from the output terminal 16.

Now, let us consider the operation of the noise reduction circuit 14. The reproduced luminance signal from the separation circuit 11 is subjected to dropout compensation in a dropout compensation circuit 17 and a 1H delay circuit 18, then FM demodulated in an FM demodulator 19, and then passed through a low-pass filter 2.
0, unnecessary frequency components are removed and the signal is supplied to the subtracter 21, while the signal delayed by 1H in the 1H delay circuit 18 is FM demodulated in the FM demodulator 22, and then unnecessary frequency components are removed in the low-pass filter 23. The components are removed and supplied to the subtracter 21. In the subtracter 21, the output signal of the low-pass filter 23 is subtracted from the output signal of the low-pass filter 20, and the noise component contained in the reproduced luminance signal is extracted.

The noise component taken out from the subtracter 21 is attenuated in the high frequency range by a de-emphasis circuit 24, then limited in amplitude to a certain level by a limiter 25, amplified in the high frequency range by a pre-emphasis circuit 26, and then sent to an attenuator 27 to increase its amplitude. It is attenuated to 1/2 and supplied to the mixer 28. In the mixer 28, the output signal of the attenuator 27 is subtracted from the output of the low-pass filter 20, and a reproduced luminance signal with noise components suppressed is extracted. At this time, the frequency versus level characteristic of the conventional de-emphasis circuit 24 is linear as shown by the broken line in FIG. 2, while the frequency versus level characteristic of the pre-emphasis circuit 26 is also linear as shown in FIG.

By the way, the frequency of crosstalk components in home VTRs and the like is, for example, around 1.3MHz after demodulation, and in order to obtain a high quality image, this crosstalk component must be suppressed.

However, in the conventional circuit described above, no consideration is given to the frequency of this crosstalk component, and therefore, if the amplitude of the beat due to crosstalk exceeds the limiter level of the limiter 25, it cannot be suppressed sufficiently. The disadvantage was that the screen flickered, making it impossible to obtain a high-quality screen.

Therefore, as a conventional circuit for eliminating the above-mentioned drawback, as shown in FIG.
There is a circuit in which a mixer 30 for mixing the output of the limiter 25 and the output of the high-pass filter 29 is connected. According to this method, large-amplitude crosstalk components can be suppressed, but it has the disadvantage that the number of circuits increases because it is necessary to further add a high-pass filter 29 and a mixer 30 to the circuit shown in the first diagram.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

The noise reduction circuit according to the present invention has a first
In the figure, the frequency versus level characteristic of the de-emphasis circuit 31 is set to be particularly greatly attenuated only around 1.3MHz, as shown by the solid line in Fig. 2, while the frequency versus level characteristic of the pre-emphasis circuit 32 is shown by the solid line in Fig. 3. As shown in , it is set to particularly greatly enhance only the frequency around 1.3MHz.

Here, if the frequency of the noise component extracted from the subtracter 21 is other than around 1.3MHz, the level is attenuated in the de-emphasis circuit 31 with the same characteristics as the conventional circuit shown in FIG.
After the amplitude is limited by the pre-emphasis circuit 3
2, the signal is level-enhanced with characteristics similar to those of the conventional circuit shown in FIG. 1, and is supplied to the attenuator 27.

On the other hand, the noise extracted from the subtractor 21 is
If the crosstalk between channels is around 1.3MHz, the de-emphasis circuit 31
The signal is particularly greatly attenuated with the characteristics indicated by the solid line shown in the figure, and is supplied to the limiter 25. At this time, since the frequency versus level characteristic of the de-emphasis circuit 31 is set as described above, even if the amplitude of the crosstalk component is large, it is attenuated to a level that is not subject to amplitude limitation by the limiter 25.
can definitely pass.

The crosstalk component that has passed through the limiter 25 is supplied to a pre-emphasis circuit 32, where it is particularly greatly amplified with the characteristics shown by the solid line shown in FIG.

Other configurations and operations are the same as those of the conventional circuit shown in FIG. 1, so their explanations will be omitted.

Note that the frequency at which the level is particularly attenuated and enhanced in the de-emphasis circuit 31 and the pre-emphasis circuit 32 is not limited to the frequency of inter-channel crosstalk as in the above embodiment, and may be set to a frequency that causes moiré, for example.
The same effect as above can be obtained.

Furthermore, since the circuit according to this embodiment is applied only to the playback system of a home VTR, it is possible to play back signals recorded on a VTR not equipped with this circuit without any problems, causing compatibility problems. Never.

As mentioned above, the noise reduction circuit according to the present invention improves the frequency characteristics of the de-emphasis circuit by
The level attenuation in a specific frequency band is set to be larger than the amount of level attenuation in other frequency bands, and the frequency characteristics of the pre-emphasis circuit are set to be larger in this specific frequency band than the amount of level enhancement in other frequency bands. When noise of a specific frequency with an amplitude larger than the limiter level comes in, it can be attenuated by the de-emphasis circuit and passed through the limiter, thereby setting the frequency characteristics of the de-emphasis circuit and the pre-emphasis circuit linearly. It can reliably suppress large amplitude noise compared to conventional circuits, and
Compared to conventional circuits, there is no newly added circuit, so the circuit can be configured easily, and furthermore, it has the advantage of being able to appropriately select a specific frequency of a signal to be suppressed.

[Brief explanation of drawings]

Figure 1 is a block diagram of a general home VTR.
Fig. 2 is a frequency versus level characteristic diagram of the de-emphasis circuit in the conventional circuit and the circuit of the present invention, Fig. 3 is a frequency versus level characteristic diagram of the pre-emphasis circuit in the conventional circuit and the circuit of the present invention, and Fig. 4 is a diagram of the main parts of the conventional circuit. It is a block system diagram. 11... Luminance signal, chromaticity signal separation circuit, 13...
... Adder, 14 ... Noise reduction circuit, 1
6...Output terminal, 18...1H delay circuit, 21,
28...Subtractor, 25...Limiter, 27...Attenuator, 31...De-emphasis circuit, 3
2...Pre-emphasis circuit.

Claims (1)

[Claims] 1. A noise reduction circuit that extracts a signal considered to be a noise component contained in an input information signal through a de-emphasis circuit and a limiter, and subtracts and extracts the output of the limiter from the input information signal after passing through a pre-emphasis circuit, The frequency characteristics of the de-emphasis circuit are set to be larger in a specific frequency band than the level attenuation in other frequency bands, while the frequency characteristics of the pre-emphasis circuit are set to be larger than the level attenuation in other frequency bands only in the specific frequency band. A noise reduction circuit characterized by being set larger than that of the noise reduction circuit.