JPS6041823A - Reduction device of impulsive noise - Google Patents

Abstract

PURPOSE:To reduce remarkably an impulsive noise existing in an input signal by providing a circuit acting as a de-emphasis circuit while the pulse noise does not exist and acting as a linear interpolation circuit while the noise exists. CONSTITUTION:While no pulse noise exists in an input audio signal, a switch circuit 25 is turned off and a switch circuit 27 is turned on in an impulsive noise reduction device, an amplifier 23 acts as an inverse amplifier, the reduction device acts as a de-emphasis circuit, and on the other hand, while the pulse noise exists, the switch circuit 25 is turned on and the switch circuit 27 is turned off, the amplifier circuit 23 stops amplification and the reduction device acts as a linear interpolation circuit. Thus, the impulsive noise included in the input audio signal is reduced remarkably.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to the prevention of external contamination into the audio signal system of audio equipment, radio receivers, television receivers, video tape recorders, video disk players, etc. The present invention relates to a pulse noise reduction device that can reduce the pulse noise in an audible manner.

(Prior art) Pulse noise, for example, ignition noise of a car or pulse noise generated by other electrical equipment, can be applied to the audio signal system of various equipment such as electrical equipment or electronic equipment that has an audio signal system. It is well known that the quality of the audio signal deteriorates if the mixture is mixed.

Conventionally, as a means to reduce the deterioration in the quality of audio signals caused by the above-mentioned pulse noise, there are two methods: (a) reducing the gain of the signal transmission system that operates during the period when pulse noise is occurring; or by cutting off the signal transmission system (reducing the gain to zero, employing a squelch circuit) to reduce pulse noise; (b) during periods of pulse noise; The most common noise reduction method that has been put into practice is to try to reduce pulse noise by maintaining the signal level of the signal at the signal level just before the pulse noise period. , these methods (a) and (b) have the disadvantage that the signal is lost during the pulse noise period, and
Even by applying the above-mentioned means (a) and (b), there has been a problem that a sufficient noise reduction effect cannot be obtained.

By the way, in order to interpolate the signal loss that occurs during the noise period, after converting the analog signal to a digital signal, a correction signal corresponding to the signal loss portion is created by applying the linear prediction method, and the correction signal is used to eliminate the noise. Interpolation of period signals has also been adopted in some digital devices, but this method requires the use of complex and expensive circuits. Such solutions have not been applied to general audio equipment.

Now, as mentioned above, when the pulse noise mixed in the signal is reduced, signal loss occurs depending on the period of existence of the pulse noise. The problem is that an audio signal of good quality cannot be obtained, and the interpolation of missing portions of the signal to solve the aforementioned problems requires the use of complex and expensive circuits. The problem is that it is difficult to apply to general audio equipment.

In order to solve the above-mentioned conventional problems, the applicant company first uses a differentiator circuit, a sample hold circuit, and a signal having slope information of the desired signal during the period when pulse noise occurs in the input audio signal. signal correction configured to be able to remove pulse noise in an input audio signal and linearly interpolate a desired signal during a period in which pulse noise occurs by being supplied with a control signal and a control signal; An analog circuit with a simple circuit configuration consisting of circuits, etc. is used to create a correction signal that can interpolate the missing part of the signal during the period when pulse noise occurs, thereby making it possible to obtain a high-quality audio signal. A pulse noise reduction device was proposed.

FIG. 1 is a block diagram of the previously proposed pulse noise reduction device. In FIG. 1, ■ is an input terminal for an input audio signal S1 mixed with pulse noise, and 2 is a delay circuit. , C8G is the pulse noise detection circuit 10
and a pulse shaping circuit 11, and this control signal generating circuit C8G generates a pulse width corresponding to a period in which pulse noise mixed in the input audio signal Sl exists. Control signal S2
is generated.

The control signal S2 generated from the control signal generation circuit C8G described above is required to correspond correctly to the position on the time axis of the pulse noise mixed in the input audio signal. By the time the generating circuit C8G detects the pulsed noise mixed in the input audio signal and generates the control signal S2 with a pulse width corresponding to the period in which the pulsed noise exists, Since there is a predetermined time delay determined depending on the operating characteristics of the pulse noise detection circuit 10 used, the pulse noise mixed in the input audio signal and the pulse noise generated in correspondence with the pulse noise are generated. The input audio signal supplied to the input terminal 1 is delayed by the delay circuit 2, which has a delay time approximately equal to the time difference between the control signal S2 and the control signal S2. To ensure that signal processing is performed correctly at locations where pulsed noise exists in an input audio signal.

The input audio signal S1 is indicated by a in FIG.

This is the information input audio signal S1 to which the required time delay has been given by the delay circuit 2, and the presence position of the pulse noise mixed in the input audio signal S1 shown in a in FIG. This correctly matches the position on the time axis of the control signal S2 indicated by b in the figure.

In addition, in Fig. 2, the input audio (for No. 4).

Time t1 → time t2, time t3 → time t4, time t5 →
Pulse noise Nl, N2 . It is exemplified as containing N3.

In FIG. 1, 3 is an amplifier having low output impedance characteristics, 4 is a switch that performs on/off operation according to the control signal S2, and 6 is a capacitor used to store a correction voltage for linear supplementary operation. 7 is a non-inverting amplifier (in-phase amplifier) having a gain G, and a capacitor 6 used to store a correction voltage for performing the linear interpolation operation described above is connected to the output side of the switch 4 and the non-inverting amplifier (in-phase amplifier). A resistor 8 is connected between the input side of the non-inverting amplifier (in-phase amplifier) 7 and the ground. A feedback circuit is provided by a series connection circuit with the capacitor 5. 9 is an output terminal.

The switch 4 described above controls the pulse noise Nl, N2 . During the period corresponding to the position of N3, the control signal S2 generated by the control signal generating circuit C8G turns off the switch 4, and the switch 4 generates pulse noise Nl, N2 in the input audio signal S1. ．． It is turned on during the period when N3 is not present.

Since the output impedance of the amplifier 3 is extremely low, the terminal voltage of the capacitor 6 when the switch 4 is turned on as described above is equal to the voltage of the input audio signal S1; It is output to the output terminal 9 via the non-inverting amplifier (in-phase amplifier) 7.

That is, when the switch 4 is turned on as described above, the input side of the non-inverting amplifier (common mode amplifier) 7 is connected via the switch 4 to the output side of the amplifier 3, which has an extremely low output impedance. Because it has been
A feedback circuit consisting of a series connection circuit of a resistor 8 and a capacitor 5 connected between the output side and the input side of the non-inverting amplifier (common mode amplifier) 7 has stopped operating as a feedback circuit, and therefore As mentioned above, the terminal voltage of the capacitor 6 connected to the input side of the non-inverting amplifier (common-mode amplifier) 7 is outputted to the output terminal 9 via the non-inverting amplifier (common-mode amplifier) 7.

Next, pulse noise N in the input audio signal S1
l, N2. When the switch 4 is turned off by the control signal S2 generated by the control signal generation circuit C8G, the capacitor 6 receives the input audio signal immediately before the switch 4 is turned off. The voltage of signal S1 is stored.

The terminal voltage stored in the capacitor 6 described above has a gain G
At the same time, it is amplified and outputted by the non-inverting amplifier (common-mode amplifier) 7, and at the same time, it is input to the input side of the non-inverting amplifier (common-mode amplifier) 7 via a feedback ffi circuit consisting of a series-connected circuit of a resistor 8 and a capacitor 5. will be returned. By the feedback operation by the feedback circuit described above, the output voltage of the non-inverting amplifier (in-phase amplifier) 7 is divided by the capacitor 5 and the capacitor 6 and stored in the capacitor 6. This is repeated in FJJl'JI, but since the capacitor 5 and resistor 8 function as a differential feedback circuit, as will become clear from the analysis results described later using mathematical formulas, the input audio signal Sl
The circuit between the output side of the switch 4, which is turned off during the period when noise is present, and the output terminal 9 functions similarly to a differentiating circuit.

Therefore, the output signal of the non-inverting amplifier (in-phase amplifier) 7 in the previously proposed pulse noise low-frequency device shown in Figure 1 is as follows.
As shown in the signal S3 shown in FIG. 2C, the duration of noise in the input audio signal S1 is sent to the output terminal 9 as a linearly interpolated signal S3.

Next, a of FIG. 3 shows a circuit diagram of a circuit portion corresponding to a circuit portion that performs a linear interpolation operation in the already proposed pulse noise reduction device shown in FIG. Referring to FIG. 3, b, etc., which shows a circuit diagram based on a frequency domain display when the switch SW in a is in an off state, the switch SW in a is in an off state during a period when noise is occurring in the input audio signal Sl. A circuit between the output side of the switch 4 and the output terminal 9 that receives the input audio signal S.
The details of the above-mentioned linear interpolation operation performed during the existence period of noise of 1 will be explained using mathematical expressions.

First, clarifying the correspondence between each component in the circuit layout shown in FIG. 3a and each component in the circuit layout shown in FIG. In each component, amplifier AI (a in Figure 3) and amplifier 3 (Figure 1), switch SW (a in Figure 3) and switch 4 (Figure 1), non-inverting amplifier (in-phase amplifier) A2 (a, b in Figure 3), non-inverting amplifier (in-phase amplifier a) 7 (Figure 1), capacitor CI (a in Figure 3), capacitor 5 (Figure 1), capacitor C2 (Figure 3) a)
The capacitor 6 (FIG. 1), the resistor R (a in FIG. 3), and the resistor 8 (FIG. 1) correspond to each other.

As described above, when there is no noise in the input audio signal S1, the switch S at a in FIG.
W is in the on state, and the input signal V is input to amplifier A.
Non-inverting amplifier (common mode amplifier) via I and switch SW
Although added to the input side of A2, the above-mentioned switch SW
is turned off as described above immediately before noise occurs in the input audio signal S1.

Now, the terminal voltages of the capacitors CI and C2 immediately before the above-mentioned switch SW is turned off are e10. When e 20 is the output signal Vo(s) when the switch Sw is turned off, the output signal Vo(s) is expressed as the following equation (1).

And the current 1 (s) flowing through the resistor I is.

It can be expressed as

Therefore, the human input signal Vi(s) is expressed by the following formula (3)% Formula% (3) Now, if the gain of the non-inverting amplifier (in-phase amplifier) A2 is G, the output signal Vo(s) is expressed as Vo(s). ) = GVi(s) --(4)(4
), as described in (3) above.

From equation (4), the output signal Vo(s) is expressed by equation (5) below.

Here, the capacitor C2 is expressed as C2=CG-1)C1・・・・・・・・・・・・(6
) (6), the output signal Vo(s) is
When 'I'1=CI·R, it becomes as shown by the following equation (7).

If the time just before the switch SW is turned off is tl, the signal voltage is V(tl), so the capacitor C
1, C2 terminal voltage e 10. e 20 is the following (8
) is shown by the formula.

By substituting equation (8) into equation (7) above, the output signal VO(S) described above becomes as shown by the first-order equation (9),
Further, when the equation (9) is transformed into an inverse Laplace transform, the equation (10) is obtained.

Vo(t) ”G (V(tl)+V'(tl)(t-
tl)) -・-(10) Since the above-mentioned equation (10) omits the second-order differential term and lower parts of the Taylor series, The linear auxiliary circuit consists of the non-inverting amplifier (in-phase amplifier) 7 in FIG. 1 (the non-inverting amplifier shown in a and b in FIG.
When the gain of the common-mode amplifier (corresponding to A2) is G, the capacitance value C2 of the capacitor 6 (corresponding to capacitor C2 shown in FIG. )5 (corresponding to capacitor C1 shown in FIG. 3a), which is (G-1) times the capacitance value C1,
That is, when the capacitance value C2 of the capacitor 6 satisfies the relationship C2=(G-1)C1 shown by the above equation (6), the slope of linear interpolation is V' (Ll), that is,
It can be seen that a linear interpolation operation given by a first-order differential voltage is performed.

(Problems to be Solved by the Invention) In the previously proposed pulse noise reduction device explained with reference to FIGS. 1 to 3, the signal level of the signal supplied to the input terminal 1 is The white noise level ratio is small,
In addition, when there is white noise with a relatively high signal level in the high range of the audio frequency band, the white noise in the high range changes the slope of the signal, causing pulsed noise. A malfunction occurs in the interpolation operation performed during the period in which the signal is missing, which not only prevents the signal from being interpolated correctly during the period where the signal is missing, but also causes problems such as the generation of new noise that follows the randomness of white noise. Because of this, prior art devices have the disadvantage that they cannot be applied well to signals from sources with low signal level to white noise level ratios.

In addition, the conventional device also handles cases where the signal to be processed is a so-called pre-emphasized signal, that is, a signal in which the high-frequency components of the signal are emphasized. The same disadvantages arise as in the case of a signal from a signal source with a small signal level to white noise level ratio, as described above.

Next, this point will be explained with reference to FIG.

Figure 4 shows how an audio signal is recorded as a frequency modulated wave.
Alternatively, it is a block diagram showing a schematic configuration of a recording and transmission system for signals that are configured to be transmitted, and in this FIG. 14 is a frequency modulator, 15 is a recording medium (A transmission line, 16 is a demodulation circuit, 17 is a demodulation circuit, 17 is a demodulation circuit, ,1
B+! di power terminal, and the above-mentioned de-emphasis,
De-emphasis characteristic (
Yo,()! 1. As is well known, the above-mentioned pre-emphasis 4 + 1 and continuous emphasis characteristics are mutual; 1.1 '1iiiri・[■/l (It is considered to indicate gender.

Now, as shown in Fig. 4, the δ self-recording (0), or in the transmission system, the recording medium power 11'') has been reproduced (No. 48), or has been transmitted through the transmission line (No. 3) On the other hand, the low sound of /(/l/s JliTAt as mentioned above)
f5. When applying the device, πM FJ
ii' The de-emphasized JJ and previous audio signals, such as the output signals of each of the 16 filters, are arranged so that they are given as input signals to the sound reduction device. It takes 1 force and 4.

In other words, it contains pulse-like irregularities (No. 3 waste, which is de-emphasized by the de-emphasis circuit 17 and is
The pulse noise in the middle of 4B when the emphasis circuit 17 is weak is caused by the de-emphasis characteristic as shown in curve H in Fig. 5, and the noise time +lJ of the pulse noise is expanded. Therefore, if the output signal from the de-emphasis circuit 17 is applied to a pulse noise reduction device configured as described above, it will be difficult to perform a good interpolation operation on the signal. It is.

Therefore, the signal to be given to the pulse noise reduction device must be an audio signal obtained from the signal transmission path to the input side of the de-emphasis circuit, but the signal is the audio signal before de-emphasis is applied. is in a state where it is emphasized by pre-emphasizing its high frequency components,
When a signal in such a state is supplied to the pulse noise reduction device described above, the pulse noise reduction device can perform an interpolation operation well during the period in which the pulse noise occurs in the signal. The fact that this is not the case will be well understood from the explanations given so far.

As is clear from the above description, in the conventional pulse noise reduction device described above, in the case of a signal in which a signal from a signal source with a small signal level to white noise level ratio is pre-emphasized, , since it is difficult to perform a good interpolation operation, a solution to it was sought.

(Means for solving the problem) The present invention detects pulse noise in an input audio signal including pulse noise, and has a pulse IJ corresponding to a period in which the pulse noise occurs. means for generating a control signal, and the above-described control corresponding to the pulse noise in the input audio signal (the control signal generated by the generation means in item i, and the control signal between the control signal and the corresponding pulse noise). Means for delaying an input audio signal including pulsed noise by a delay circuit having a delay time approximately equal to the time difference; By supplying a signal having slope information of the desired signal during the period in which pulsed noise occurs, it is possible to perform a linear interpolation operation on the desired signal during the period in which pulsed noise occurs, and the input audio A pulse noise reduction device is equipped with a linear interpolation circuit and a de-emphasis circuit that are configured to always perform de-emphasis operations during periods when no pulse noise occurs in the signal. As a combined circuit for the above linear interpolation circuit and de-emphasis circuit, the input audio signal is supplied to the inverting amplifier via the first resistor, and a '2nd resistor is connected between the input and output of the above-mentioned inverting amplifier. and a first switch circuit that is turned on during the period when pulse noise is occurring, and a parallel connection circuit between the output side of the inverting amplifier and the input side of the non-inverting amplifier. , a second switch circuit that is turned off during the period in which pulse noise is occurring is connected, and a first switch circuit is connected between the input side of the above-mentioned inverting amplifier and the input side of the above-mentioned non-inverting amplifier. A device for reducing pulse noise using a circuit in which a series connection circuit of a second capacitor and a third resistor is connected between the input and output of the above-mentioned non-inverting amplifier. was provided.

(Example) Hereinafter, specific contents of the pulse noise reduction circuit of the present invention will be explained in detail with reference to the accompanying drawings. FIG. 6 is a block diagram of an embodiment of the pulse noise reduction device of the present invention, and (,) in FIG. 7 shows the pulse noise shown in FIG. Further, FIG. 7(b) is an equivalent circuit diagram of the pulse noise reduction apparatus shown in FIG. 6 in an area where pulse noise exists.

In the block diagram of an embodiment of the pulse noise reduction device of the present invention shown in FIG. 6, 19 is an input terminal for the input audio signal S1 mixed with pulse noise;
20 is a delay circuit, and C3G is a control signal generation circuit constituted by a pulse noise detection circuit 32 and a pulse shaping circuit 33. A signal from this control signal generation circuit C8G is mixed into the input audio left signal S1. A control signal S2 having a pulse width corresponding to the period in which the pulse noise exists is generated.

As described above with reference to FIG. 2, the control signal S2 generated from the control signal generation circuit C3G is generated by the pulse noise Nl mixed in the input audio signal Sl,
N2. Although it is necessary to correctly correspond to the position of N3 on the time axis, in the control signal generation circuit C8G,
The pulse noise Nl, N2°N3 mixed in the input audio signal S1 is detected, and the period in which the pulse noise exists is changed from time t1 to time t2 and time t3 accordingly.
→ Time t4 → Time t5 → Time t6 A predetermined time delay determined depending on the operating characteristics of the pulse noise detection circuit 32 used occurs before the control signal S2 with the corresponding pulse width is generated. Therefore, the pulse noise Nl, N2 . N
3 and its pulse noise Nl.

N2. The input audio signal S1 supplied to the input terminal 19 is delayed by the delay circuit 20 having a delay time approximately equal to the time difference between the control signal S2 generated in response to the control signal S2 generated in response to the control signal S2. Various types of signal processing to be performed are performed correctly at the positions where pulsed noises N1, N2, and N3 exist in the input audio signal S1.

In FIG. 6, 21 is an amplifier having low output impedance characteristics, and the output signal of this amplifier 21 is applied to an inverting amplifier 23 via a first resistor 22 (resistance R11). A parallel connection circuit including a second resistor 24 (resistance R12) and a first switch circuit 25 is connected between the input and output terminals of the inverting amplifier 23 described above. The first mentioned above
The switch circuit 25 is a switch circuit that is turned on during a period when pulse noise is present in the input audio signal Sl.

Further, between the output side of the above-mentioned inverting amplifier 23 and the input side of the non-inverting amplifier 28, a second signal is connected between the output side of the inverting amplifier 23 and the input side of the non-inverting amplifier 28. A switch circuit 27 is connected.

The first point mentioned above. The opening/closing control operation of the second switch circuits 25 and 27 is performed based on the control signal S2 generated by the control signal generation circuit CSG described above.
The opening/closing control signal supplied to the first switch circuit 25 is
The polarity of the control signal S2 generated by the control signal generation circuit C3G is inverted by the inverter 34.

A first capacitor 26 (capacitor C11) is connected between the input side of the non-inverting amplifier 28 and the input side of the inverting amplifier 23, and a first capacitor 26 (capacitor C11) is connected between the input and output terminals of the non-inverting amplifier 28. A series connection circuit of a second capacitor 29 (capacitor Cl2) and a third resistor 30 (resistance R13) is connected to.

In the pulse noise reduction device of the present invention having the above-mentioned components, during a period in which no pulse noise occurs in the input audio signal (steady operation period), the first pulse noise reduction device in the pulse noise reduction device The switch circuit 25 is in the OFF state and is in the IL state.

The second switch circuit 27 is turned on.

In this state, the output impedance of the amplifier 23 is extremely low, so the third resistor 30 and the second capacitor 2
The positive feedback circuit formed by the series connection circuit with 9 stops operating,
The pulse noise reduction device shown in FIG. 6 is shown in FIG. 7(a).
The amplifier 23 operates as an inverting amplifier, and the output from the amplifier 23 is sent to the output terminal 31 via the amplifier 28.

The transfer function G(s) for the equivalent circuit shown in FIG. 7(a) is calculated as follows.

However, G is the gain of the amplifier 28, T is the time constant,
It is represented by T=C11·R12.

That is, in the period when pulse noise exists in the input audio signal and C does not exist, the pulse noise reduction device shown in FIG. 6, which is represented by the equivalent circuit of (,) in FIG. As such, the time constant T=C11・
This means that it operates as a de-emphasis circuit exhibiting the de-emphasis characteristics of R12.

Next, in the pulse noise reduction device shown in FIG. 6 during a period when pulse noise is present in the input audio signal, the first switch circuit 25 is turned on;
Also, since the second switch circuit 27 is in the off state, in this state, the amplification action is stopped due to the short circuit caused by the first switch circuit 25 that is in the on state between the input and output terminals of the amplifier 231. , the input and output terminals of the amplifier 23 are both at ground potential, and the first capacitor 26 is equivalent to having one end thereof grounded.

Therefore, the apparatus for reducing pulse noise shown in FIG. 6 during a period in which pulse noise exists in the input audio signal is represented by an equivalent circuit as shown in FIG. 7 (b). However, the equivalent circuit shown in FIG. 7(b) is based on the assumption that pulse noise exists in the input audio signal that is applied to the already proposed pulse noise reduction device described with reference to FIG. The equivalent circuit for the period 'C, ie, the equivalent circuit shown in FIG. 3(b), is the same as that shown in FIG.

Here, consider the terminal voltages of the capacitors c ii and C12 immediately before the second switch circuit 27 is turned off. First, the capacitor 26 (C1l) has one end connected to the inverting input terminal side of the inverting amplifier 23,
Moreover, since the de-emphasized signal V d (t 1) is applied to the other end of the capacitor 26 (Call), the terminal voltage e20 of the capacitor 26 (Call) is e20=Vd
(tl) −(12).

In addition, the terminal voltage elO of the capacitor 29 (CI2) is
The result is shown in the following (13).

elo = (01) (Vd(tl)-V'd(tl))
-413) Capacitor 26 (C1
Comparison of terminal voltage e2'0 of l) with terminal voltage e20 of capacitor 2 (C2) shown by equation (8) already mentioned, and terminal voltage of capacitor 29 (C12) shown by equation (13) With elO.

A comparison with the terminal voltage elO of capacitor 1 (C1) shown in equation (8) above shows that V(t 1) and V'(t 1) in equation (8) are respectively Vd(
t1).

v'd(tl) is replaced by the formula (Engine 2) and (13
).

That is, the pulse noise reduction device of the present invention operates as a de-emphasis circuit during a period in which there is no pulse noise in the input audio signal, and
During the period when pulse noise is present in the input audio signal, it operates as a linear interpolation circuit using the de-emphasized signal as input, and greatly eliminates the pulse noise contained in the input audio signal. Reduce to.

(Effects) As is clear from the above detailed explanation, the pulse noise reduction device of the present invention can simply attenuate the gain of the transmission system during a period in which pulse noise is mixed. Alternatively, the signal level during the period of pulsed noise is
Unlike the conventional pulse noise reduction device described above, which aims to reduce pulse noise by maintaining the signal level at the level just before the pulse noise, Since the resulting signal loss is interpolated, it is possible to effectively reduce pulse noise without causing any unnaturalness to the auditory sense, and it is also possible to implement a circuit for interpolation of the loss signal. Since it can be realized using a simple analog circuit, it is possible to easily provide audio equipment with excellent performance at low cost.

In addition, even if the level of white noise manually applied to the pulse noise reduction device of the present invention is relatively high, the level of high-frequency white noise that is enhanced by the differentiating circuit is suppressed by switching and using the de-emphasis circuit. As a result, malfunctions caused by interpolation operations in the signal correction circuit can be greatly reduced, pulse noise can be easily reduced, and the range of applications has been expanded compared to conventional devices, making it possible to greatly reduce malfunctions caused by interpolation operations in signal correction circuits. It goes without saying that it effectively reduces problematic ignition noise from cars and motorcycles, as well as pulse noise generated from electrical equipment with built-in motors. Of course, it can also be effectively applied to the reduction of pop noises caused by scratches, etc., dropout noises that occur in audio signals when signals on video discs are missing, and other types of noise.

[Brief explanation of drawings]

Figure 1 is a block diagram of the previously proposed pulse noise reduction device, Figure 2 is a waveform diagram for explaining operation, Figure 3 is an equivalent circuit diagram of the previously proposed pulse noise reduction device, and Figure 4 5 is a block diagram of an example configuration of an FM signal recording and transmission system, FIG. 5 is a curve diagram of an example of pre-emphasis characteristics and de-emphasis characteristics, FIG. 6 is a block diagram of a pulse noise reduction device of the present invention, and FIG. FIG. 2 is an equivalent circuit diagram of the pulse noise reduction device of the present invention. 1.19...Input terminal, 2,20...Delay circuit, C
8G...Control signal generation circuit, 3, 7, 23.28
... Amplifier, 10.32... Pulse noise detection circuit, 9, 31... Output terminal, 11.33... Waveform shaping circuit, 4, 25.27... Switch circuit, 5, 6
, 26, 29... Capacitor, 8, 22, 24, 3
0...Resistance, 34...Inverter,

Claims (1)

[Claims] (2) means for detecting pulse noise in an input audio signal including papal noise and generating a control signal having a pulse width corresponding to the period during which the pulse noise occurs; and a pulse in the input audio signal. A control signal generated by the above-mentioned control signal generating means corresponding to the pulse noise is generated by a delay circuit having a delay time approximately equal to the time difference between the control signal and the corresponding pulse noise. means for delaying an input audio signal, the control signal being supplied as a timing signal for operation, and a signal having slope information of a desired signal during a period in which pulsed noise in the input audio signal occurs. is supplied, so that a linear interpolation operation can be performed on the desired signal during the period when pulse noise occurs, and at the same time, during the period when pulse noise does not occur in the input audio signal, A pulse noise reduction device comprising a linear interpolation circuit and a de-emphasis circuit that are configured to perform a de-emphasis operation, the circuit being a linear interpolation circuit and a de-emphasis circuit. The input audio signal is supplied to the inverting amplifier through the first resistor, and the second resistor is connected between the input and output of the inverting amplifier.
A parallel connection circuit is connected between the resistor and the first switch circuit which is turned on during the period when pulse noise is occurring, and the output side of the inverting amplifier and the input side of the non-inverting amplifier are connected. A second switch circuit that is turned off during the period in which pulse noise is occurring is connected between the input side of the inverting amplifier and the input side of the non-inverting amplifier. A first capacitor is connected, and a series connection circuit of a second capacitor and a third resistor is connected between the input and output of the non-inverting amplifier. The reduction circuit 2, as a linear interpolation circuit, includes the first capacitor described above and the second capacitor described above.
The pulse noise reduction device according to claim 1, wherein the reciprocal of the voltage division ratio of the feedback voltage by the capacitor is set equal to the gain of the non-inverting amplifier.