JPS6313523A - Reducing device for pulselike noise - Google Patents

Abstract

PURPOSE:To reduce a pulselike noise without causing the unnaturality in the audible sense by applying linear interpolation tying signal levels at the start and end point of time in the existing period of the pulselike noise. CONSTITUTION:A terminal voltage across a capacitor C for linear interpolation rises at a prescribed slope as shown in a straight line I shown in figure (e) by charring the capacitor C for linear interpolation provided at the input side of an amplifier 11 by a prescribed current subject to voltage/current conversion from an output signal S4 from an amplifier 10 by means of a voltage/current conversion means. The state of the change in the terminal voltage is expressed as a straight line tying s signal level of an input audio signal S1 at the start point of time during the pulselike noize existing time mixed in the input audio signal S1 and a signal level of the input audio signal S1 at the end point of time during the pulselike noise existing period mixed in the input audio signal S1. Thus, an output signal S5 in the state that the existing period of pulselike noise mixed in the input audio signal S1 is subject to linear interpolation in an excellent way is outputted at an output terminal 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to an audio signal system in audio equipment, radio receivers, television receivers, video disc players, and other equipment. The present invention relates to a pulse noise reduction device that can reduce pulse noise in an audible manner.

(Prior art) Pulse noise, such as car ignition noise 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 if such a substance is mixed in, the quality of the audio signal will deteriorate.

Conventionally, methods for reducing the quality deterioration of audio signals caused by the above-mentioned pulse noise include (a) reducing the gain of the signal transmission system during the period in which pulse noise occurs, or A method that attempts to reduce pulse noise by cutting off the transmission system (reducing the gain to zero... employing a squelch circuit);
(b) Maintaining the signal level of the signal during the period of pulsed noise at the signal level immediately before the period of pulsed noise,
A method that attempts to reduce pulse noise has been put into practical use as the most common noise reduction means.

(Problems to be Solved by the Invention) However, the conventional pulse noise reduction means as described in (a) and (b) above have the disadvantage that the signal is lost during the period of the pulse noise. , (a) mentioned above, (
Even by applying the method (b), there has been a problem that a sufficient noise reduction effect cannot be obtained.

Therefore, 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 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 inexpensive general audio equipment.

Now, as mentioned above, when the pulse noise mixed in the signal is reduced, it is possible that the signal loss occurs in correspondence with the period of existence of the pulse noise. The problem is that audio signals of good quality cannot be obtained, and in order to solve the above-mentioned problems, it is necessary to use complex and expensive circuits to interpolate the missing parts of the signal. However, since it is difficult to apply it to general audio equipment,
There has been a need for a good measure to solve the above-mentioned problems.

(Means for Solving the Problems) The present invention detects pulse noise contained in an input audio signal, and detects a signal having a pulse period corresponding to the period in which the pulse noise occurs. means for generating a control signal from the end of the period in which the pulsed noise occurs; and a time delay approximately equal to the period of the pulsed noise occurring in the input audio signal. means for applying the input audio signal to the input audio signal to obtain a delayed input audio signal; first and second switches controlled to be turned off only during pulses of the control signal by the control signal; a subtraction circuit for generating a difference signal between an audio signal and the delayed input audio signal; a signal holding means provided on the output side of the first switch for controlling opening/closing of the output signal of the subtraction circuit; A linear interpolation capacitor provided on the output side of the second switch that controls the opening/closing of the delayed input audio signal, and an output signal from the signal holding means described above are connected to the linear interpolation capacitor via the voltage-current conversion means. This invention solves the conventional problems by providing a pulse noise reduction device comprising supplying means.

(Example) Hereinafter, specific contents of the pulse noise reduction device of the present invention will be explained in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the pulse noise reduction apparatus of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the pulse noise reduction apparatus shown in FIG. 1.

In FIG. 1, reference numerals 1 and 3 are input terminals of a pulse noise reduction device, and this input terminal 1 has an input audio signal 81 mixed with pulse noise ((a in FIG. 2)). ) is supplied. Further, 2 is an output terminal of the pulse noise reduction device, and from this output terminal 2 is output an output audio signal in which the existence period of the pulse noise in the input audio signal is linearly interpolated. . In Fig. 1, the dotted line connecting input terminals 1 and 3 indicates that when input terminal 3 is not provided, the input signal supplied to input terminal 1 is applied to the control signal generation circuit C8G through the connection shown by the dotted line. This indicates that the

In the example shown in the first diagram, the control signal generation circuit C8G is composed of a pulse noise detection circuit 4, a waveform shaping circuit 5, and a delay circuit 6, and detects pulse noise mixed in the input audio signal Sl. The control signal 82 ((h in FIG. )).

Also, SWI and SW2 are the first. a second switch, the first switch; The second switches swt and sW2 are switched and controlled by the above-described control signal so as to be in an OFF state only during the period of the pulse width τ of the control signal. In Fig. 1, SUB is a subtraction circuit, C is a linear interpolation capacitor, ch is a hold capacitor, 7,
9 to 11 are amplifiers.

The input audio signal S supplied to the input terminal 1 described above
1 is amplified by an amplifier 7 having a low output impedance and then given as an input to a delay circuit 8.
It is given to the subtraction circuit SUB as a minuend signal. Also,
The delay circuit 8 applies a time delay τ approximately equal to the period τ of the pulse noise occurring in the input audio signal S1 supplied to the input terminal 1 to the input audio signal S1. A delayed input audio signal Sld as shown in FIG. 2(f) is output.

The delayed input audio signal Sld output from the delay circuit 8 is amplified by the amplifier 9 with low output impedance and then sent to the output terminal 2 via the second switch SW2.
and the delayed input audio signal S
ld is supplied to the subtraction circuit SUB as a subtraction signal.

The above-mentioned subtraction circuit SUB converts the human audio signal 81 shown in FIG.
Delayed input audio signal Sl shown in (f) of the figure
After subtracting d, the signal S3 shown in (Q) of FIG. 2 is output.

That is, the output signal S3 from the subtraction circuit SUB described above is combined with the input audio signal S1 shown in FIG. delayed input audio signal S
The signal S3 is obtained by adding the signal -8ld shown in FIG. 2(b) in which the polarity of the signal ld is inverted.

The output signal S3 from the subtraction circuit SUB described above is supplied via a first switch SWI to the input side of an amplifier 10 having a high input impedance.

Since a hold capacitor channel is connected between the input side of the amplifier 10 and the ground, the signal S4 shown in FIG. 2(d) output from the amplifier 10 is as follows.
During the period when the first switch SWI is in the on state, the state is the same as the output signal S3 shown in (Q) of FIG. 2, which is output from the subtraction circuit SUB. Moreover, during the period when the switch SWI is turned off, the signal level of the signal S3 described above at the time when the switch SWI is turned off is a constant signal level held by the hold capacitor ch. It is a signal of the state of

Now, as shown in FIG. 2(a), the input audio signal S1 supplied to the input terminal 1 of the pulse noise reduction device changes during the time period to-*tl, t3→t4. - Assuming that each includes pulse noise, the first switch SWI changes from time t1 to t2 and t4.
→It is turned off by the control signal S2 sent from the control signal generation circuit C8G during the period t5.

As a result, the first switch SW1 cuts off the signals in the period from time t1 to t2 and the period from time t4 to t5 in the signal S3 supplied from the subtraction circuit SUB, but as described above, The above-mentioned first switch S that controls opening and closing of the output signal S3 from the subtraction circuit SUB
Since a hold capacitor ch is provided on the output side of WI, the hold capacitor ch holds the signal level of the signal S3 at time t1 after time tl, and holds the signal level of the signal S3 at time t4 after time t4. maintain the signal level.

As mentioned above, the signal level of the output signal S3 from the subtraction circuit SUB held by the hold capacitor ch is as shown in (a) of FIG. 2 and (b) or (f) of FIG. As is clear, the signal level of the input audio signal S1 at the end of the period of existence of the pulsed noise mixed in the input audio signal S1 and the period of existence of the pulsed noise mixed in the delayed input audio signal Sld The delayed input audio signal Sl at the starting point of
The difference between the signal level of d, that is, 1, the signal level of the input audio signal S1 at the end of the existence period of the pulse noise mixed in the input audio signal S1 and the pulse nature mixed in the input audio signal S1 This is the difference from the signal level of the human-powered audio signal S1 at the start point of the noise period.

The above points will be explained with reference to the waveform diagram shown in FIG. 2 as follows. The first switch SWI which controls the opening/closing of the output signal S3 from the subtraction circuit SUB described above is generated by the control signal generating circuit C8G (h) in FIG.
The control signal S2 shown in FIG. 1 is turned off during the period from time t1 to t2 and from time t4 to t5.

At times t1 and t4, which are the starting points of the respective periods when the first switch SWI is turned off, the state of the input audio signal S1 supplied as the minuend signal to the subtraction circuit SUB is as follows. As is clear from FIG. 2(a), this corresponds to the state of the input audio signal S1 at the end of the period of existence of the pulsed noise mixed in the input audio signal S1, and also corresponds to the state of the input audio signal S1 as described above. FIG. 2 shows the state of the delayed input audio signal Sld that is supplied as a subtraction signal to the subtraction circuit SUB at time t1 and time t4, which are the starting points of the respective periods when the first switch SWI is turned off. of (f
) or, as is clear from FIG. 2(b), corresponds to the state of the delayed input audio signal Sld at the beginning of the existence period of the pulse noise mixed in the delayed input audio signal Sld, and , since the delayed input audio signal Sld and the input audio signal S1 are simply shifted on the time axis, it is the beginning of the existence period of the pulse noise mixed in the delayed input audio signal Sld. The signal level state of the delayed input audio signal Sld at the time point is the same as the signal level state of the input audio signal S1 at the beginning of the existence period of the pulsed noise mixed in the input audio signal 81, and therefore The signal level of the output signal S3 from the subtraction circuit SUB held by the hold capacitor ch is as shown in (a) in FIG.
As shown in b) or (f), the signal level of the input audio signal S1 at the end of the existence period of the pulsed noise mixed in the input audio signal S1 and the delayed input audio signal -Dio signal Sl
The difference in signal level between the signal level of the delayed input audio signal Sld at the start point of the existence period of the pulsed noise mixed in d, that is, the signal level difference at the end of the existence period of the pulsed noise mixed in the input audio signal S1. It corresponds to the signal level difference between the signal level of the input audio signal S1 at the time and the signal level of the input audio signal S1 at the beginning of the existence period of the pulse noise mixed in the input audio signal S1.

The signal S4 outputted from the amplifier 10 described above is applied to the input side of the amplifier 11 via a resistor R.

Using a resistor R having a high resistance value,
Furthermore, by using a high input impedance as the amplifier 11 described above, the amplifier 1
The output signal S4 from 0 is voltage-current converted and applied as a constant current to the input side of the amplifier 11 described above.

During the period in which the high-level control signal S2 is being sent from the control signal generation circuit C8G, the second switch SW2 is turned off.
In this state, the linear interpolation capacitor C provided on the input side of the amplifier 11 is charged by a constant current obtained by converting the output signal S4 from the amplifier 10 into a voltage current by the voltage current converting means. , the terminal voltage of the linear interpolation capacitor C described above is (
The line I shown in e) is rising at a constant slope, but the state of change in the terminal voltage of the linear interpolation capacitor C is based on the input audio signal 81.
(a) of the input audio signal Sl at the beginning of the existence period of the pulse noise mixed in the input audio signal S1 (level 6 and a at the end of the existence period of the pulse noise mixed in the input audio signal S1) input audio signal S
It is a straight line connecting the signal level of 1, therefore.

In the pulse noise reduction device of the present invention shown in FIG. 1, the output (1t 'j' S 5 (see (g) in FIG. 2) can be sent to the output terminal 2.

The mode of change in the terminal voltage of the linear interpolation capacitor C provided on the input side of the amplifier 11, which is charged by a constant current obtained by converting the output signal S4 from the amplifier 10 described above, is as described above. As is clear,
Input audio signal S at the beginning of the existence period of pulsed noise mixed in input audio signal S1
1 and the signal level of the input audio signal S1 at the end of the existence period of the pulse noise mixed in the input audio signal S1. Depending on the slope of the original signal applied, (e) in FIG.
The period from time t1 to t2 shown in , or time t
In the period from 4 to t5, the straight line rises at a predetermined slope like the example shown in each case, or the straight line rises at a predetermined slope in the example shown in FIG. becomes a straight line with an opposite slope, allowing for good signal interpolation.

Further, during a period in which the high-level control signal S2 is not sent from the control signal generation circuit C8G, the first and second switches SWl and SW2 are turned on, and the amplifier 11 Since the input side of is connected to the output side of the amplifier 9 having a low output impedance via the second switch SW2 which is turned on, in this state, the input side of the amplifier 10 is connected to the output side of the amplifier 9 having a low output impedance. Even if the output signal S4 is supplied as a current to the input side of the amplifier 11 via the resistor R having a high resistance value, the current flows toward the output side of the amplifier 9 which exhibits the low output impedance described above. The linear interpolation capacitor C is not charged even by the current, and the output signal S
5 will not be adversely affected.

As is clear from the above, the amplifier 1 described above
The signal sent from output terminal 1 to output terminal 2 is one in which the period in which pulsed noise is mixed in delayed input audio signal Sld is well linearly interpolated.

(Effects) As is clear from the above detailed explanation, the pulse noise reduction device of the present invention detects the pulse noise contained in the input audio signal, and detects the pulse noise that is generated. control signal generating means for generating a signal having a pulse width corresponding to the period in which the pulse noise occurs as a control signal from the end of the period in which the pulse noise occurs; and a pulse occurring in the input audio signal. means for obtaining a delayed input audio signal by applying a time delay approximately equal to the period of the sexual noise to the input audio signal; first and second switches; a subtraction circuit that generates a difference signal between the input audio signal and the delayed input audio signal; and the first switch that controls opening and closing of the output signal of the subtraction circuit. A signal holding means provided on the output side, a linear interpolation capacitor provided on the output side of the second switch that controls the opening/closing of the delayed input audio signal, and an output signal from the signal holding means described above to convert it into a voltage and current. A pulse noise reduction device comprising means for supplying the linear interpolation capacitor via the conversion means,
In the pulse noise reduction device of the present invention, the signal level at the beginning of the period of existence of the pulse noise mixed in the input audio signal S1, and the period of existence of the pulse noise mixed in the input audio signal S1. An output signal subjected to linear interpolation that connects the signal level at the end of the signal level can be generated by a device with a simple circuit configuration, and the pulse noise reduction device of the present invention The gain of the transmission system is simply attenuated during the pulse noise period, or the signal level during the pulse noise period is maintained at the signal level of the signal immediately before the pulse noise. Unlike the conventional pulse noise reduction device described above, which aims to reduce pulse noise, interpolation of signal loss that occurs during the period of pulse noise is also performed. It is possible to effectively reduce pulse noise without causing unnaturalness, and the circuit configuration for interpolating missing signals can be realized with a simple analog circuit, making it possible to reduce costs at a low cost. The pulse noise reduction device of the present invention can easily provide audio equipment with excellent performance, and the pulse noise reduction device of the present invention can reduce ignition noise from automobiles, motorcycles, etc., pulse noise generated from electrical equipment with built-in motors, and audio equipment. It can be effectively used to reduce pop noise caused by dust or scratches on a disc, dropout noise that occurs in an audio signal when a video disc signal is missing, and other pulse noises. It should be noted that the pulse noise reduction device of the present invention is suitable for use with, for example, a rotating magnetic head type when used for reducing pulse noise in a case where the period of existence of the problematic pulse noise is always approximately constant. When used to reduce pulse noise generated during the switching period of a rotating magnetic head in a magnetic recording/reproducing device, the delay circuits 6 and 8 used in the device are used to reduce the pulse noise that causes the problem described above. Since it is sufficient to use a delay circuit 6.8 whose delay time is set to a delay time equal to the length of the existence period of the sexual noise, it can be implemented with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the pulse noise reduction device of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the pulse noise reduction device.

Claims (1)

[Claims] Pulse noise contained in the input audio signal is detected, and a signal having a pulse width corresponding to the period in which the pulse noise occurs is detected at the end of the period in which the pulse noise occurs. means for generating a control signal as a control signal from the input audio signal; and means for obtaining a delayed input audio signal by applying a time delay approximately equal to the period of pulse noise occurring in the input audio signal to the input audio signal. and a first and second switch controlled to be turned off only during the pulse width period of the control signal by the control signal, and a difference signal between the input audio signal and the delayed input audio signal. a subtraction circuit for generating a signal, a signal holding means provided on the output side of the first switch for controlling the opening and closing of the output signal of the subtraction circuit, and a second switch for controlling the opening and closing of the delayed input audio signal. A pulse noise reduction device comprising: a linear interpolation capacitor provided on the output side of the circuit; and means for supplying the output signal from the signal holding means to the linear interpolation capacitor via voltage-current conversion means.