JPS5923931A - Reducing device of impulsive noise - Google Patents

Abstract

PURPOSE:To attain the linear interpolation to a desired signal during the period when impulsive noise exists and to eliminate the impulsive noise in an input signal, by supplying a signal having ramp information of a desired signal during the period when impulsive noise exists in an input audio signal, and a control signal. CONSTITUTION:The input audio signal outputted from a delay circuit 2 is applied to an input terminal 5a of a signal correcting circuit 5. A control signal S2 generated at a control signal generating circuit CSG is given to a control signal input terminal 5c of the signal correcting circuit 5. A signal S3 as shown in Fig. (c) is given to an output terminal 5b by applying a signal S5 having ramp information of the desired signal to a terminal 5d. The output signal S3 is outputted to an output terminal 8 of the device and given to a differentiating circuit 6 to output a differentiating signal shown in Fig. (d). A differentiated output signal S4 is applied to a sample-and-hold circuit 7 and a signal S5 is outputted from the sample-and-hold circuit 7. When the signal S5 is fed to the terminal 5d, the signal correcting circuit 5 performs linear interpolation of the missing part based on the ramp information of the desire signal supplied in the signal S5 by forming a correcting signal so that the missing part of the signal in the input audio signal is interpolated linearly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is aimed at reducing pulse noise mixed externally into the audio signal system of audio equipment, radio receivers, television/computer receivers, video disk players, etc. The present invention relates to a device for reducing pulse noise that can be reduced perceptually well.

(Prior art) Pulse noise, such as the ignition noise of a car, is caused by pulse noise generated by other electrical equipment in 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 audio (No. 6) deteriorates when noise is mixed in.

Conventionally, as a means to reduce the deterioration in audio signal quality caused by the above-mentioned pulsed noise, there are two methods: (a) reducing the gain of the signal transmission system during the period in which pulsed noise occurs; (b) A method that attempts to reduce pulse noise by cutting off the signal transmission system (lowering the gain to zero... employing a switch circuit); (b) A method that attempts to reduce the signal level of the signal during the period of pulse noise. , a method that attempts to reduce pulse noise by maintaining the signal level just before the pulse noise period, etc. has been put into practical use as the most common noise reduction method. The means (a) and (b) have a 1/-5 drawback when the signal is lost during the period of pulse noise, and the application of the means (a) and (b) mentioned above also has a noise reduction effect. is obtained sufficiently, and the problem is that T(I/- and ψ) are v-f.

By the way, in order to interpolate the signal loss that occurs during the noise period, after converting the analog signal into a differential 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 to row rl'l, J:5 is also used in some differential equipment, but it requires the use of complex and expensive circuits to implement the interpolation. Since this is necessary, such a solution is not applied to general audio equipment. (Problem to be solved by the invention) Even if pulse noise is reduced, if signal dropout occurs in correspondence with the duration of the pulse noise, it will not be possible to obtain a good quality audio signal even by reducing the pulse noise. and V-
In addition, in order to solve the above-mentioned problems, interpolation of missing portions of the signal requires the use of complex and expensive circuits, which is a common problem. The problem is that it is difficult to apply to audio equipment.

(Means for Solving the Problems) The present invention provides a differential circuit, a sample hold circuit, and a control signal that is supplied with a signal having slope information of a desired signal during a period in which pulse noise occurs in an input audio signal. A signal correction circuit, etc., configured to remove pulse noise in an input audio signal and linearly interpolate a desired signal during a period in which pulse noise occurs. An analog circuit with a simple circuit configuration creates a correction signal that can interpolate the missing part of the signal during the period when pulse noise occurs, thereby obtaining a high-quality audio signal. The present invention provides a noise reduction device.

(Example) Hereinafter, specific contents of the pulse noise reduction device of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of an embodiment of the pulse noise reduction device of the present invention, and in this FIG. input terminal,
2 is a delay circuit, and C3G is a control signal generation circuit constituted by a pulse noise detection circuit 3 and a pulse shaping circuit 4. A signal from this control signal generation circuit C8G is mixed into the input audio signal SI. A control signal s2 is generated with a pulse width corresponding to the period in which the pulse noise is present.

As the pulse noise detection circuit 3 and the pulse shaping circuit 4 in the control signal generation circuit C8GK, appropriate ones are selected from well-known configurations. The control signal S2 is required to be mixed into the input audio signal, but the control signal S2 is required to be mixed into the input audio signal.
By the time the pulse noise mixed in the input audio signal is detected and the control signal S2 having the pulse width corresponding to the period in which the pulse noise exists is generated according to the vibration, the control signal S2 is used. Since there is a predetermined time delay depending on the operating characteristics of the pulse noise detection circuit 3,
1. The pulse noise mixed into the input audio signal and the pulse noise generated in response to the pulse noise. The input audio signal that has not been supplied to the input terminal 1 is delayed by the delay circuit 2 having a delay time f, which is approximately equal to the time difference between f and the control signal, and performs various operations to be performed by the control signal S2 described above. To ensure that signal processing is performed correctly at locations where pulsed noise exists in an input audio signal. The input audio signal SI shown by a in FIG. 2 is the input audio signal S1 given the required time delay by the delay circuit 2, and is the input audio signal S shown by a in FIG. The location of the mixed pulse noise and the control signal S2 indicated by b in FIG.
The position on the time axis corresponds correctly.

Note that in FIG. 2, the time t is
I-+t2, time t3→t4, time t, →t6, pulse noise N, , N2. It is exemplified that N3 is mixed in.

In FIG. 1, the input audio signal output from the delay circuit 2 is supplied to the input terminal 5a of the U correction circuit 5.
It is as shown by the circuit inside the boot 5 in the figure, and the control signal S2 generated by the control signal generation circuit C8G is applied to the control signal input terminal 5c, and
Since the signal S having slope information of the desired signal (e in FIG. 2) is not supplied to the terminal 5d, the output terminal 5b receives a signal S3 as shown in C in FIG. 2, that is, the input audio signal S. , the pulse noise in V is removed, and the desired signal in the period in which the pulse noise occurs is linearly interpolated. ・No. S
3 is sent. Details of the signal correction circuit 5 described above will be described later with reference to FIG. 3.

The output (g S) from the signal correction circuit 5 described above is output to the output terminal 8 of the device and is also supplied to the differential path 6. The differential circuit 6 is shown in C in FIG. The differential signal S3 shown in FIG. 2 is differentiated to output a differential signal S as shown in FIG.

The differential signal S4 described above exhibits a phase difference of 90 degrees with respect to the original signal (desired signal), the output signal 83 from the signal correction circuit 5, etc., and is linearly interpolated into the signal S3 described above. A signal section exhibiting a constant signal level is generated corresponding to a signal section exhibiting a constant slope in the current signal interval (a period during which pulsed noise existed in the original signal). being done.

Then, the signal level of the signal section showing the above-mentioned constant signal level in the differential signal S4 becomes a positive signal level or a negative signal level depending on the direction of the slope in the original signal. The polarity differs depending on the # slope direction of the original signal, and the difference between the signal level of the signal section showing a constant signal level in the differential signal S4 and the zero level is determined according to the degree of slope in the original signal. The size changes and there are 7x and 7x.

The differential output signal S4 output from the differentiating circuit 6 is supplied to the sample and hold circuit 7.
A signal S as shown in e of FIG. 2 is outputted from the circuit.

This signal S, when the device is operating in a steady state, is
This is the same as the signal S4 described above. The sample and hold circuit 7 is essential for operation until the device enters steady state operation. The sampling bar/res for the sample hold circuit 7 described above is as follows:
The control signal S2 generated by the control signal generation circuit C8G is used.

The sample and hold circuit 7 outputs a signal S,
has a signal section showing a constant signal level corresponding to a signal section showing a constant signal level in the differential signal S4 described above, and as described above, a constant signal section in the differential signal S4 described above is provided. 5. The signal section indicating the level indicates the slope information of the original signal (desired signal). The output signal S from the sample hold circuit 7 is also
The above-mentioned signal section showing a certain signal level contains the slope information of the desired signal.

Tirs signal S6 output from sample hold circuit 7
, that is, a signal S having slope information of the desired signal,
is supplied to the terminal 5d of the correction circuit 5, the signal correction circuit 5 calculates the signal that occurred during the pulse noise mixing period in the input audio signal based on the slope information of the signal S and the desired signal. A correction signal is created in which the missing portion is linearly interpolated 5, the missing portion of the signal is linearly interpolated using the correction signal, and a signal S3 as shown in C in FIG. 2 is sent to the output terminal 8. . - Next, an example of the configuration of the differentiating circuit 6 and the sample-and-hold circuit 7, and the configuration and operation of the signal correction circuit 5 will be described with reference to FIG. In FIG. 3, the boot cross is a differential circuit 6, which is composed of a capacitor Cd, a resistor, and an amplifier A3.

First, the block 7 is a sample and hold circuit 7, which is composed of a switch SWs, a capacitor Cs, and an amplifier A4. 7a is an input terminal for the control signal S2 given as sampling, <l less, and the sample-hold circuit 7 is connected to the capacitor CsK when the switch SWs is turned off during the period when the control signal 820 is at the level of
Just before the switch b''Ws is turned off, the bell is held.

Block 5 is a signal correction circuit 5, and in the figure,
5a is an input terminal for an input audio signal, 5b is an output terminal, 5C is a supply terminal for a control signal S2, 5d is a supply terminal for a signal S, A1 is a first amplifier, and A2 is a second amplifier.
The first amplifier A1 is of low output impedance and the second amplifier A2 is of high input impedance.

In the signal transmission path between the output side of the first amplifier A and the input side of the second amplifier A2, there is a switch SW that is turned off when the control signal S2 is at the high level. Further, a charge storage capacitor C is provided between the input side of the second amplifier A20 and the ground, and a variable constant current circuit VC is provided on the input side of the second amplifier A2.
The output side of the resistor R1 is connected to the power supply +Vcc.
Transistor X1 to which 14 pins are connected via
A positive power supply +Vcc is connected to a transistor X2 whose collector is connected to the collector of the transistor X1, and a resistor connected between the emitter of the transistor X2 and the negative power supply -Vcc. It is composed of a resistor R3- connected between the negative power source -Vcc, a variable resistor ■, and a series connection circuit of the resistor R1.The base of the transistor X1 is connected between the resistor and the variable resistor ■. Connect to the connection point, and also connect the transistor X2
The base of is connected to the connection point between resistor R4 and variable resistor ■.

The variable resistor ■ is used to correct imbalances in the circuit due to variations in the characteristics of the component parts of the (b) path, and if the circuit can be balanced correctly, it can be replaced with two fixed resistors. You can also do that.

The variable constant current circuit (■) operates under a standard operating condition such that when the voltage at the terminal 5d is zero, the voltage at the %2 point is zero, and when the voltage at the terminal 5d is positive. Time is 2
The voltage at the point becomes the same positive voltage as the voltage at terminal 5d,
Further, when the voltage at the terminal 5d has negative polarity, the voltages at the two points have the same negative polarity as the voltage at the terminal 5d.

Therefore, at two points of the variable constant current circuit vc, there is a voltage having a polarity and a voltage value corresponding to the polarity and magnitude of the signal in the signal section indicating a constant signal level in the signal S applied to the terminal 5d. Since it appears, the above rs Z
If a capacitor C is connected between the point and the ground, the capacitor C has the same polarity as the signal of the signal section 111 indicating a certain signal level in the signal S, and the polarity of the signal S,
The battery is charged with a constant charging current determined in accordance with the signal level of the signal in the signal section showing a constant signal level.

In the signal correction circuit 5 in FIG. 3, pulse noise is mixed into the input audio signal S1 so that v=7. (In this state, the control signal S2 supplied to the terminal 5c is at a low level, so the switch SW is turned on. Therefore, the input audio signal S1 supplied to the input terminal 5alC is transmitted to the first amplifier. It passes through the signal transmission path A, → switch SW → second amplifier A2 → output terminal 5b, and is transmitted from the input terminal 5a to the output terminal 5b.At this time, there is a connection between the signal transmission path and the ground. The charge storage capacitor C shown on the tangent line shows a terminal voltage value according to the voltage value of the signal transmitted to the signal transmission path described above.It should be noted that pulse noise is mixed in the input audio signal S1. In the above state where the variable constant current circuit V
The output terminal of C is connected to the output side of the first amplifier A1, which has an extremely low output impedance of approximately zero ohm, via the switch SW which is in the on state. Corresponding to the signal S applied to the constant current circuit VC via the terminal 5d, the current f generated in the variable constant current circuit (■) and output from the variable constant current circuit with high output impedance is approximately zero ohm as described above. The current generated from the low output variable constant current circuit VC does not cause any trouble to the desired signal transmitted from the first amplifier A to the second amplifier A2. However, as a signal to be supplied to the variable constant current circuit VC, it is not necessary to extract and supply only the signal in the signal section showing a constant signal level in the signal S. The output signal S of the sample and hold circuit 7 may be supplied as is to the VC.

Next, when pulse noise is mixed in the input audio signal Sl, a control signal S2 is generated corresponding to the period in which the pulse noise N1 to N3 is occurring, and the control signal S2 is generated over the high level and low level periods of the control signal S2. ℃ switch 8W is turned off. By not turning off the switch SW described above, the terminal voltage of the capacitor C is lower than that of the switch SW described above.
The signal level is maintained as it was when the control signal S2 was turned off (when the control signal S2 was set to high level).

In addition, since the terminal 5d of the variable constant current circuit VC is given a signal in a signal section indicating a constant signal level in the signal S in that state, the variable constant current circuit
With the polarity corresponding to the polarity of the signal S, which is applied to terminal 5d,
In addition, a constant current value corresponding to the signal level is outputted, thereby charging the charge storage capacitor C. The charging operation for the charge storage capacitor C is performed over a period in which pulse noise is occurring, and the terminal voltage of the capacitor C increases linearly to -
However, as soon as the pulse noise is no longer mixed in, the control signal S2 becomes low level and the switch SW is turned on, so that the accumulated charge in the capacitor C is reduced by the low output impedance of the first amplifier Discharges instantly.

The variable current (b) path ■ is the signal S2 supplied to the terminal 5d.
That is, by being driven by a signal S having the slope information of the desired signal at a polarity and a constant signal level, the polarity and the constant signal level according to the polarity of the pulse S and the signal level are changed. A current of current value is caused to flow into the charge storage capacitor C, and the terminal voltage of the capacitor C is linearly increased with a slope corresponding to the signal level with the polarity of the signal in the signal section indicating a constant signal level in the signal S5. Before the terminal voltage of capacitor C is increased by the inflow of current from variable constant current circuit VC,
Since the terminal voltage of is the signal level of the input audio signal immediately before the switch SW is turned off, there is no signal loss that occurs in the signal corresponding to the period of pulse noise mixed in the input audio signal S1. It is clear that linear interpolation is performed well by the above-described operation of the signal correction circuit 5, and the signal S3 sent to the output terminal 9
has a waveform that approximates the original signal.

In Fig. 2, f shows the correction signal for linear interpolation generated in the signal correction circuit 5 as a solid line, and the waveform of the desired signal in the absence of pulse noise as a dotted line. f in FIG. 2 is an explanatory diagram to facilitate understanding of the operation, and in actual operation, the signal correction circuit 5 outputs the second
A signal S3 as shown in FIG. C is output.

(Effect) From the detailed explanation above, it is clear that J: Sea urchin,
The pulse noise reduction device of the present invention simply attenuates the gain of the transmission system during the pulse noise period, or changes the signal level during the pulse noise period to eliminate the pulse noise. Unlike the conventional pulse noise reduction device described above, which aims to reduce pulse noise by holding the signal level at the signal level of the immediately preceding signal, Since interpolation is also performed for the missing signals that occur, it is possible to effectively reduce the pulse noise without causing any unnaturalness in the auditory sense. The circuit configuration can be realized with a simple analog circuit, and it is possible to easily provide audio equipment with excellent performance at a low cost.

Note that the pulse noise reduction device of the present invention can be expected to have a sufficient screening effect when the time span in which pulse noise occurs is narrow; however, when the time span in which pulse noise occurs is wide, The correction effect may be slightly reduced. However, ignition noise caused by automobiles and motorcycles, etc., noise generated from electrical equipment with built-in electric motors,
It goes without saying that it can be effectively applied to pulse noise caused by dust or scratches on audio discs, pop noise caused by dust or scratches on audio discs, trottle-out noise that occurs in audio signals when video disc signals are missing, and other pulse noises. be.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the pulse noise reduction device of the present invention, FIG. 2 is a waveform diagram for explaining operation, and FIG. 3 is an example configuration of a signal correction circuit and its related circuits. FIG. 1...Input terminal, 2...Delay (b) path, C8G...
- Control signal generation circuit, 3...-pulse noise detection circuit. 4... Pulse shaping circuit, 5... Signal correction circuit, 7.
...Sample hold circuit, 8...Output terminal. VC: Variable constant current circuit, C: Charge storage capacitor, A, , A2: 1st. Second amplifier, A5. A
4...Amplifier, SW, SWs...Switch, ・,,,,,,6i \ t, "l t3'i, tsl t2 t4j6" mouth

Claims (1)

[Claims] 1. Detecting pulse noise in an input audio signal including pulse noise, and detecting the noise caused by the pulse noise.
a first control signal generated by the control signal generating means in response to pulsed noise in the human audio signal; means for delaying an input audio signal containing pulsed noise by a delay circuit approximately equal to the time difference between the input audio signal and the corresponding pulsed noise; By supplying a signal having slope information of the desired signal during the period when pulse noise occurs in the audio signal, the pulse noise removal operation and the linear correction for the desired signal during the period when pulse noise occurs are performed. means for supplying the output signal of the delay circuit to a signal correction circuit configured to perform the operation 1'; means for supplying the output signal from the signal correction circuit to the output terminal and the differentiation circuit; Means for applying the output signal of the differentiator circuit to the sample bold circuit to which the control signal described above is supplied as a sampling pulse, and the period during which pulse noise is generated in the input audio signal from the sample hold (b) path. a pulse noise reduction device 2, comprising means for outputting a signal having slope information of a desired signal in and applying the signal to the signal correction circuit described above;
As a signal correction circuit, charging operation using the output current of the variable constant current circuit to the charge storage capacitor is performed only during the period when pulse noise occurs, and discharging operation is performed instantaneously at the end of the said period. The pulse-based noise range circuit 3 according to claim 1, which uses a circuit configured as follows, a first amplifier with a low output impedance and a second amplifier with a high input impedance, as a signal correction circuit. and a switch circuit provided in a signal transmission path from the first amplifier to the second amplifier to interrupt signal transmission during a period in which pulse noise is occurring, and The output side of the variable constant current circuit, which operates so that the output current value is determined by the signal having the slope information of the desired signal during the period f during which the static noise occurs, and the charge storage capacitor are connected to the second amplifier. Pulse noise reduction device 4 according to claim 1, which is connected to the input side as a variable constant current circuit, and a current value is set according to the signal level of a human input signal to the variable constant current circuit. In order to reduce the pulse noise according to claim 3, the T is constructed so that a constant current output of γ polarity can be obtained depending on the polarity of the input signal to the T. Reduction device