JPS61158275A - Noise suppressing circuit - Google Patents

Abstract

PURPOSE:To suppress noise components over the entire frequency band by providing a primary phase equalizer to a transmission system for original video signal and a secondary HPF to a noise component extracting system and keeping a phase different pi between said equalizer and HPF over the entire frequency band. CONSTITUTION:A primary phase equalizer 15 is provided to a transmission system for original video signal SI, and a secondary HPF11 is provided to a signal transmission system which extracts the noise components. The phase characteristics of both the equalizer 15 and PHF11 are set at 180 deg. over the entire frequency band. As a result, the noise of an output video signal SO can be suppressed over the entire frequency band by adding with the same phase the signal SI passed through a delay circuit 16 and the noise suppressing signal SL passed through a limiter 13 together through a synthesizer 17.

Description

[Detailed Description of the Invention] 5 [Field of Industrial Application] This invention is applicable to VTRs, video discs (VD), etc.
The present invention relates to a noise suppression circuit used when reproducing a video signal (image signal), and particularly to a noise suppression circuit that can effectively suppress noise over a wide frequency band.

[Conventional technology]

In VTRs, video discs, and the like, a noise suppression circuit is usually provided in the video signal reproduction system.

FIG. 13 shows a conventional example of a noise suppression circuit 01 provided in such a reproduction system.

In this figure, the input video signal S□ (Figure 14) supplied to the terminal (1) is supplied to the first-order high-pass filter (2) and is limited to the frequency band shown in Figure 15. High-frequency video signal S containing noise components.

(Fig. 14B) is extracted and supplied to the limiter (4) via the amplifier (3) to suppress the high frequency video signal, resulting in almost only noise components as shown in Fig. 14C. Limiter output SL is obtained. Limiter output S
Further, L is level-adjusted by a delume (5) and then added together with the original video signal S1 by an adder (6). At this time, the limiter output SL is applied in an inverted state.

As a result, the limiter output SL is added in reverse phase to the noise component contained in the original video signal S, resulting in an output video signal S with suppressed noise components, as shown in Figure 14. - is obtained at terminal (7).

[Problem that the invention seeks to solve]

However, such a noise suppression circuit 00 has the disadvantage that it can only sufficiently suppress noise in a specific frequency band, and cannot effectively suppress noise distributed over the entire frequency band.

In other words, the phase characteristic of the high-pass filter (2) is the 16th
The phase characteristic due to the propagation delay time of the limiter (4) including the amplifier (3) is as shown by the curve a in the figure, so the overall value from the terminal (1) to the pump (5) is as shown in the curve a. The phase characteristic is as shown by curve C.

On the other hand, since the original video signal S is supplied to the adder (6) without being given phase characteristics, it is the output video signal S. The overall phase characteristics of curve C are only in reverse phase, and as a result, the angular frequency ω at which the phase becomes zero. Noise can be effectively suppressed only in a band near the frequency band and the frequency band in the vicinity thereof, and noise components existing in other frequency bands remain.

In other words, as shown in FIG.
If it is shown as , the output video signal S. Since the noise power remaining inside is like a curved platform, the angular frequency ω at which the phase becomes zero.

The noise suppression effect is maximum when

Moreover, noise power may increase more than the input power in the high frequency region. Therefore, the effect of S/N improvement is not as expected.

Therefore, the present invention solves these conventional problems and proposes a noise suppression circuit that can suppress noise components almost uniformly over the entire frequency band.

[Technical means for solving the problem] In order to solve the above-mentioned problem, in the present invention, as shown in FIG. 1, a primary phase equalizer α is provided in the transmission system of the original video signal S1. At the same time, a second-order high-pass filter Ql) is provided in the signal transmission system for extracting noise components.

Then, the phase constants of the husband and wife are selected so that their phase characteristics have only a fixed phase difference and other characteristics completely match.

[Effect]

According to this configuration, the phase characteristic of the second-order high-speed filter α is as shown by the curve f in Fig. 3, and the phase characteristic of the first-order phase equalizer 05 is as shown in the curve g, so that the entire frequency band is The phase difference between the two is π (=180°). Therefore, if the limiter output SL shown in FIG. 2 and the original video signal Sf that has passed through the primary phase equalizer 05 are added in phase, the output video signal S is obtained. )/l sky is suppressed over the entire frequency band.

When this is considered with reference to noise power, the result is as shown in Fig. 4. The song @h in the figure is the input noise power, and the song at is the output noise power. As is clear from this, the output noise power is the low cutoff frequency ω of the high-pass filter αη. It can be easily understood that the frequency band of 8 or more is sufficiently suppressed.

〔Example〕

FIG. 1 is a system diagram showing an example of a noise suppression circuit (10) according to the present invention, in which an input video signal S1 supplied to a terminal (1) is supplied to a secondary high-pass filter (10).
First step (as shown in the blade), a high-frequency video signal S□ containing noise components is extracted (Fig. 2B), and this is supplied to the limiter θ1 via an amplifier Q to suppress the high-frequency video signal. A limiter output SL (C in the same figure) containing almost only noise components is output, and this is further added to the volume a for level adjustment.
4 to the adder α power.

The input video signal Sf is further phase-equalized by a first-order phase equalizer (to) and then supplied to the above-mentioned adder 0η via a delay circuit OQ. The delay circuit 0Q is for compensating the propagation delay time caused by the amplifier α2 and limiter α3.

Note that the original video signal S that has passed through the primary phase equalizer OF9,
and limiter output SL are added in phase.

By the way, the transmission frequency U, (S) of the above-mentioned first-order phase equalizer CIQ (where s = jω, and ω indicates the input angular frequency) is as follows, and the phase characteristic φEQ at that time is (s) is -1ω
... (2) φ・q(s) = −2tm;.

If this is illustrated, it will look like the curve g in Figure 3.

On the other hand, a second-order high-pass filter (1η transfer function H
HPF(l!I) is generally, however, ω. is the cutoff angular frequency I PilrHz
Since it is given by degree, Qc(
=0.5), +z Equation (3) becomes as follows.

1...(“)=8・+2GJ s + s・°(
5) Phase characteristic φHpF when Qe is selected as above
(sX!) This is illustrated as curve f in Figure 3.

Therefore, the phase characteristic φ shown by equation (2). , in (S), ω. = ω. ... If (8) is selected, the phase characteristic φ8Q of the primary phase equalizer (2)
(11) becomes . As a result, (7) do. That is, the curves f and g are phase-shifted by only π over the entire frequency band, and the phase amounts at each frequency completely match in absolute value.

Therefore, as shown in Fig. 1, if the limiter output SL including the phase characteristics due to the propagation delay time and the original video signal S1, which is also delayed by the time corresponding to the propagation delay time, are added in phase by an adder αη, , the noise components mixed into the original video signal S can be effectively suppressed over the entire frequency band by the limiter output SL.

That is, as shown in FIG. 4, the noise power present in the original video signal, that is, the input video signal S1, is distributed with uniform strength over the entire frequency band as shown by the curve. When this is supplied to the noise suppression circuit α1, the cutoff angular frequency ωe
In the frequency band above μ, noise power is uniformly suppressed as shown by curve 1.

Note that the cutoff angular frequency ω. Although the noise power is not sufficiently suppressed in the nearby frequency band, this is because the noise suppression circuit On itself suppresses the noise components present in the relatively high frequency side among the noise components included in the input video signal S□. This is because the noise component on the low frequency side is not suppressed.

Now, the above-mentioned secondary high-pass filter C11) is the fifth-order high-pass filter C11).
A high pass filter having an R, C, L configuration as shown in the figure can be used. On the other hand, the primary phase equalizer 09 is
An equalizer using a transformer T and capacitor C as shown in the figure can be used.

When using the second-order high-pass filter (11) shown in FIG. 5, if each phase constant is selected as The phase characteristic φl'l P F ('' can be obtained.

6 to 8 show other examples of the second-order high-pass filter αυ that can be used in the present invention. That is, a first-order 71-pass filter (with a C, R configuration as shown in FIG. 6)
A second-order high-pass filter αJ can be constructed by using two IIA) and (IIB) and cascading them via a buffer amplifier (IIC), and as shown in Fig. 7, Even if two first-order high-pass filters (12A) and (12B) of R and L configuration are used and these are connected in cascade via a buffer amplifier (IIC), a second-order high-pass filter α can be constructed. can do. Furthermore, a first-order high-noise filter (13A) with a C9R configuration and a first-order high/4' filter (13B) with an R,L configuration as shown in FIG.
Even if cascaded through (IIC), secondary high, 41
A filter α force can be constructed.

FIG. 10 shows another embodiment of the noise suppression circuit 01 according to the present invention. In this example, a second-order high-pass filter and a second-order low-nos filter are combined to obtain the phase characteristic of the curve f in FIG. 3.

In this case, a second-order Lag-Lsad low-pass filter is used as the low-pass filter 01), and this is connected to the next stage of the limiter α3. A limiter wire is further connected via.

In this configuration, the cutoff frequency of the secondary high-pass filter αη is set to a higher cutoff frequency than in the case shown in FIG. In this example 2-3M
Hz.

In this way, when the cutoff frequency of the second-order high-pass filter αη is selected high, the high-frequency components of the input video signal S1 extracted by this high-pass filter α]) are reduced, and the output video signal S. This is because the high frequency characteristics of .

Now, in the configuration j shown in Fig. 10, the transfer functions Hf and PF (' of the second-order low-pass filter 21) are given by where K is a constant, and ω□ and ω5 are the second-order low-pass filters 21). A main meter that determines the shape of the filter characteristic, where ω□ is the angular frequency of the shoulder on the high frequency side, ω is the angular frequency of the shoulder on the low frequency side, and O4>O1.

Now, in this configuration, the transfer characteristic of the noise component due to the filter (11) and 0°C is as follows.So, if we select the phase constant of the second-order loaf four-pass filter Qη so that The transfer characteristic shown is I2, and the transfer characteristic is equivalent to that when using the second-order high-pass filter 01) shown in FIG.
Also in the case of the figure, the angular frequency ω of the first-order phase equalizer αB.

For this, ωL : O0°゛°(2) If Q second-order low-pass filters O1 are selected, the phase characteristics shown in Fig. 3 can be obtained even with this configuration, and the noise component can be reduced. The trick is to effectively suppress the entire frequency band.

In the configuration shown in FIG. 10, the delay time of the delay circuit 0O is determined by the amplifier z, (a) and the limiter 03. The total propagation delay time including (c) is set.

FIG. 11 shows yet another embodiment of the invention.

In the above-mentioned video signal reproducing device, a low-pass filter is generally provided before the noise suppression circuit α1 to limit the band of the reproduced video signal and then supply it to the noise suppression circuit αO for noise suppression processing. is running. In this case, in order to compensate for the delay characteristics caused by the low-pass filter (1) shown in FIG. 11, a phase equalizer 0 is provided between this low-pass filter and the noise suppression circuit α1.

In other words, when the delay characteristic of the row/matrix filter (7) is as shown in curve j in Figure 12, the phase characteristic of the phase equalizer 0 is given to compensate for this delay characteristic. . In this case, in the conventional example shown in FIG. 13, the input video signal S1 is directly supplied to the adder (6), so the phase equalizer 01) at this time is as follows.
It is necessary to use a first-order phase equalizer shown by the curve t in FIG. 12 and a second-order phase equalizer shown by the curve t.

Therefore, in the past, there was a drawback that the configuration of the phase equalizer zero power was complicated.

However, in the case of the configuration according to the present invention, since the primary phase equalizer 05 is already provided in the original video signal transmission system, the primary phase equalizer 05 is ) can also be used as a phase equalizer for delay characteristic compensation. Therefore, the phase equalizer (31) has 2
It can be configured with only the next-order phase equalizer, which has the effect of simplifying the configuration.

If the delay characteristic of the low-pass filter (7) is not the curve j in Figure 12, but has a characteristic in which the amount of delay increases on the higher frequency side, the first- and second-order phase equalizers However, even in such a case, according to the present invention, the configuration of the phase equalizer 01) can be simplified by the amount of the primary phase equalizer α. It is something.

〔Effect of the invention〕

As explained above, in the present invention, a primary phase equalizer is provided in the transmission system of the original video signal S1, a secondary high/IP filter is provided in the signal transmission system for extracting noise components, and their phase characteristics are The phase constants of the husband and husband are selected so that the two have only a fixed phase difference and the other characteristics are completely matched.

According to this configuration, the phase difference between the two is π (=1800) over the entire frequency band, so that the output video signal S. noise components can be suppressed over the entire frequency band.

Therefore, a better noise suppression effect than before is exhibited,
Playback image quality can be significantly improved.

Further, in the conventional noise suppression circuit, the high frequency component of the original video signal S is subtracted by the high frequency component of the video signal included in the limiter output tag, so that the high frequency characteristic deteriorates. On the other hand, in this invention, a larger S improvement effect can be obtained than the conventional one, so when reducing the volume α4 to obtain the same 87N improvement effect as the conventional one, the video signal included in the limiter output SL Since the level of the high-frequency component (the positive and negative contour generated by the second-order high-intensity filter α℃) is also very low, the high-frequency component of the original video signal s1 is subtracted by this K. The proportion of

Therefore, in this case, in addition to the above-mentioned effects, the output video signal S. It is possible to improve the high-frequency characteristics of the conventional system.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an example of a noise suppression circuit according to the present invention, FIG. 2 is a waveform diagram for explaining its operation, FIGS. 3 and 4 are characteristic curve diagrams for explaining its operation, and FIG. 8 to 8 are block diagrams showing an example of a second-order ronnos filter, FIG. 9 is a block diagram showing an example of a first-order phase equalizer, and FIGS. 10 and 11 are block diagrams showing other examples of the present invention. Systematic diagram shown,
Figure 12 is a characteristic curve diagram to explain the operation of Figure 11, Figure 13 is a system diagram of a conventional noise suppression circuit, Figure 14 is a waveform diagram to explain its operation, Figure 15, and Figure 11. is a characteristic curve diagram also used to explain the operation. ◇1 is a noise suppression circuit, <I is a secondary high-pass filter, α], (c) is a limiter, α9 is a primary phase equalizer, e
l) is a second-order low-pass filter, 0η is an adder, Sl is an original (input) video signal, SH is a high-frequency video signal, SL is a limiter output, and So is an output video signal. Koshi C11J
Q bran gQ (1) Rashim gJ Arashi-1

Claims (1)

[Claims] The input video signal is supplied to a primary phase equalizer and a secondary high-pass filter, and a high-frequency video signal containing noise components output from the secondary high-pass filter is level-limited by a limiter. This high-frequency video signal and the original video signal output from the primary phase equalizer are added together, and the phase characteristics of the secondary high-pass filter and the
The phase characteristic of the next phase equalizer is 180 over the entire frequency band.
A noise suppression circuit in which the respective phase constants are selected so as to have a phase of .degree.