JPH0323718Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention is a pulse noise removal device for audio broadcast wave receivers used in AM receivers, FM receivers, etc.
In particular, the present invention relates to a pulse noise removal device for a receiver that detects noise from a received signal containing external noise and performs waveform shaping processing on a reproduced audio signal based on the detected noise to remove only the noise.

[Prior Art] It is known that many interference waves are received along with desired waves in audio broadcast waves such as AM broadcast waves and FM broadcast waves, and one of these received waves includes pulse noise, for example. There is.

In particular, in car-mounted receivers, this noise is often generated not only from external sources but also from the own vehicle, so a pulse noise removal device is installed inside the receiver to counteract this noise. .

For example, Fig. 6 shows a block diagram of the circuit configuration of a pulse noise removal device in a conventional AM receiver, and Fig. 7 shows the output waveforms of each component in Fig. 6. There is.

In Fig. 6, 1 is an AM antenna, 2 is a frequency converter, 3 is a high-pass filter, 4 is a detection circuit, 5 is a switch pulse generation circuit, 6 is a band-pass filter, 7 is a detection circuit, and 8 is an audio signal. A processing circuit, 9 an output stage, and 10 a speaker.

In other words, AM antenna 1 receives broadcast waves, and frequency converter 2 converts them to a predetermined intermediate frequency (IF).
After converting the audio signal into the audio signal, the audio signal is restored by a bandpass filter 6 and a detection circuit 7, and further, predetermined signal processing is performed by an audio signal processing circuit 8, and the audio signal is reproduced by a speaker 10 via an output stage 9.

However, the above-mentioned pulse noise is present in the received signal 1.
When superimposed on the signal a, the waveform of the IF signal 2a is generated as the output of the frequency converter 2 as shown in FIG. It will be included.

Therefore, in this AM receiver, the high-pass filter 3 removes 15k of the mixed pulse noise.
Hz or higher components are separated, detected by the detection circuit 4, the detected output is used to drive the switch pulse generation circuit 5, and pulse noise is removed by signal processing by the audio signal processing circuit 8. ing.

Below, the operation of removing pulse noise will be explained in detail using FIG. 7.

As shown in the figure, t= of the intermediate frequency signal 2a
If pulse noise is superimposed on _t1 , the output of the detection circuit 7 via the bandpass filter 6 will still be the audio signal 7a with added noise.

This pulsed noise interference wave is not limited to the broadcast wave band of carrier frequency ±9 kHz like the AM modulated wave of audio, so it contains high frequency components.

Therefore, if this intermediate frequency signal 2a is passed through the high-pass filter 3, only the pulsed noise of high frequency components will be extracted, and if this is detected by the detection circuit 4, a pulsed noise waveform 4a will be obtained, and further switch pulse generation will occur. When passed through the circuit 5, a pulse 5a with a wide τ time width is obtained as shown in the figure.

This pulse 5a causes the audio signal processing circuit 8 to
is driven to remove only the pulse noise contained in the audio signal 7a output from the detection circuit 7.

That is, in the signal processing of the audio signal processing circuit 8, the waveform-shaped processed signal 8a in which the signal amplitude level has fluctuated is used instead of the pulse noise portion (τ time width) of the audio signal 7a when gain control is performed. In addition, in the case of hold-type control, the waveform-shaped processed signal 8 is obtained by holding the amplitude level of the leading edge to which the pulse noise is added for a period of τ.
We will get b.

As described above, in the conventional pulse noise removal device, the processed signals 8a and 8b shown in FIG.
Measures were taken to remove pulse noise contained in audio signals.

[Problem to be solved by the invention] However, in the conventional pulse noise removal measures described above, although the processed signal 8b has a better noise removal effect than the processed signal 8a shown in FIG. In order to obtain the waveform of the signal 8a, the circuit configuration is more complicated than that used to obtain the waveform of the signal 8a, and the discontinuous portion (hold portion of the τ time) occurring in the waveform of the audio signal may be perceived by the listener. It had many shortcomings.

Furthermore, in the case of the signal 8b, when the frequency of the audio signal becomes high, the reproduced sound becomes as shown in the signal 8c, and the listener has the disadvantage that the discontinuous sound becomes more audible to the listener.

On the other hand, although the above-mentioned processed signal 8a has the advantage of simplifying the circuit configuration, depending on the timing of _t1 shown in the figure, the audio signal is cut off for a time τ like the signal 8a'. Therefore, when the listener listens to the reproduced sound through the speaker 10, the listener often perceives a clicking sound.

Regarding this click sound, a waveform showing a transient sound is shown in Fig. 5, and the click sound is easily perceived for waveforms with steep rises and falls, as shown in pulses a and b. In addition, as shown in pulses c and d, if the time width T of the rise and fall of the transient sound is increased and the waveform is made with a gentle slope, the click sound is generally less perceptible. known to.

In other words, it is known that if the slope is changed, the listener's perception of the click sound changes, and whether or not the click sound is perceived is approximately determined by the above-mentioned time width T.

This can be seen, for example, in Miyasaka, Sakai, “Perception of clicks during signal interruptions” Journal of the Acoustical Society of Japan Vol. 36244-
252pp (1980), according to which T>
It has been disclosed that if the time is 5 ms, the click sound is difficult to perceive.

Therefore, from the above, the time width T is approximately T > 5ms.
If set to , it is possible to suppress the perception of the click sound, but no improvement measures have been taken in the conventional pulse noise removal device described above.

Purpose of the invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide a pulse noise removal device for a receiver that suppresses the interference of the click sound when removing pulse noise. .

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a receiving means for inputting a received signal, detecting the signal, and outputting a detected signal, and a receiving means for inputting a received signal, detecting the signal, and outputting a detected signal; noise detection means for detecting pulsed noise and outputting a noise signal; and a waveform shaping process for extracting a low frequency component of the noise signal and making the transient slope of the low frequency component gentle with a predetermined pulse width. a waveform shaping means for obtaining a waveform shaped signal; It is characterized by comprising a delay means for outputting the output, and a gain control means for controlling the gain of the delayed detection signal using the waveform shaping signal.

[Operation] According to the pulse noise removal device for a receiver according to the present invention, the low frequency component of the noise signal included in the detected signal is extracted, and the transient partial slope of the low frequency component, that is, the rising edge, is extracted with a predetermined pulse width. Then, a waveform-shaped signal is obtained which has been subjected to waveform-shaping processing so that the fall is gradual.

Then, the detected signal is delayed for a predetermined time so that the noise signal included in the detected signal exists at a predetermined timing of the waveform shaping signal pulse width, and the gain of the delayed detected signal is controlled by the waveform shaping signal. . As a result, it is possible to obtain an audio signal in which only pulse noise is removed and click sounds are not perceived.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram of an AM receiver showing an example of a pulse noise removing device according to the present invention, and FIG. 2 is an explanatory diagram showing output waveforms of each component shown in FIG. 1.

Incidentally, the same members as in FIG. 6 of the prior art mentioned above are given the same reference numerals, and their explanations will be omitted below.

In FIG. 1, reference numeral 11 denotes a low-pass filter and waveform shaping circuit, which is composed of a low-pass filter 30 and a waveform shaping circuit 32. 12 is a delay circuit; 13 is a gain control circuit;
The configurations of 9 and 10 are the same as those shown in FIG. 6 described above.

In FIG. 2, when the intermediate frequency signal 2a is input to the detection circuit 4 through the high-pass filter 3, the output of the detection circuit 4 becomes a pulse noise waveform 4b with a pulse width τ, and at t=t ₁ . It has occurred.

When this pulse waveform 4b is input to the switch pulse generation circuit 5, the output of the circuit 5 becomes a switch pulse 5b with a pulse width τ, which is input to the low-pass filter and waveform shaping circuit 11.

Here, when the switch pulse 5b is first input to the low-pass filter 30 of the circuit 11, the filter 30 blunts the pulse 5b and outputs a waveform 11a shown by a solid line.

Next, in the waveform shaping circuit 32, the waveform 1
1a is input, and a waveform-shaped signal 11b is outputted from the circuit 11 to the gain control circuit 13 by waveform shaping processing of slicing along C-C' as shown by the broken line.

That is, in this waveform shaping process, the slope of the transient portion is made gentle at pulse fall time τ ₄ and pulse rise time τ ₅ .

On the other hand, when the intermediate frequency signal 2a is input to the detection circuit 7 through the bandpass filter 6, its output waveform becomes an audio signal 7b containing pulse noise, as shown by the solid line, and this signal 7b is When input to the delay circuit 12, the pulse noise is delayed by τ ₁ hour, resulting in a delayed signal 1 shown by a broken line waveform.
It becomes 2a.

Here, the delay time τ ₁ of the delay circuit 12 is set so that the pulse noise included in the audio signal 7b falls within the sliced pulse width of the low-pass filter output waveform.

That is, in principle, the rough output waveform 1 obtained by the aforementioned low-pass filter 30
1c is sliced at an amplitude level of A-A' or B-B', and the delay time is set so that the pulse noise portion falls within the pulse width τ _k .

Therefore, for example, the delay circuit 12 shown in FIG.
Therefore, if the pulse noise superimposed on the audio signal 7b is delayed by τ ₃ hours as the delayed signal 12b, then the signal 12b becomes the waveform-shaped signal 11b described above.
can be located approximately in the middle of the pulse width. This delayed signal 12a is then output to the gain control circuit 13.

From the above, in the gain control circuit 13,
Gain control is performed on the output waveform 12b from the delay circuit 12 using the output waveform 11b from the circuit 11,
As a result, a gain-controlled output waveform 13a is obtained.

In this gain control output waveform 13a, the above-mentioned C
The pulse fall time τ ₄ and pulse rise time τ ₅ are determined by the waveform shaping process of the -C′ slice, and these times τ ₄ and τ ₅ are designed to be difficult to perceive with the auditory sense. If the time is set larger than the time T, the listener will not perceive the click sound and will not be bothered by it.

In the embodiment shown in FIG. 1, the audio signal is
Although the example is shown using a monaural signal of an AM receiver, the present invention can of course also be applied to an FM receiver that uses stereo right-ear signals and left-ear signals.

Fig. 3 shows another embodiment of the pulse noise removal device according to the present invention, and is an example of an FM receiver to which a stereo signal is applied, and Fig. 4 shows the output waveforms of each part of Fig. 3 described above. It is a diagram.

Incidentally, the same members as in the above-mentioned figures are given the same reference numerals, and the description thereof will be omitted below.

In the figure, 14 is an FM antenna, 15 is a frequency converter, 16 is a limiter, 17 is a discriminator, 18 is a high-pass filter, 19 is a detection circuit, 20 is a pulse shaping circuit, 21 is an audio signal processing circuit, and 22 is a de-emphasis circuit.

That is, in this FM receiver, the frequency of the received signal from the FM antenna 14 is converted to a predetermined intermediate frequency (IF) by the frequency converter 15, the amplitude is limited by the limiter 16, and the frequency is changed by the discriminator 17. - Amplitude conversion is performed, thereby resulting in an audio signal 17a containing a pulse noise component.
is outputting.

Then, the high-frequency component of, for example, 200 kHz or more is separated by the high-pass filter 18, and the pulse noise 18a containing only pulses of the high-frequency component mixed in the audio signal 17a is extracted. The signal is detected and further subjected to pulse shaping processing by the pulse shaping circuit 20, and a pulse shaped signal 20a is output to the audio signal processing circuit 21.

Therefore, in the audio signal processing circuit 21, for example, the pulse shaping signal 20a is used as a gate pulse to remove the pulse noise component contained in the audio signal 17a output from the discriminator 17, and the de-emphasis circuit Output to 22.

That is, when the audio signal processing circuit 21 is a gate circuit, the waveform of the audio signal 17a containing pulse noise is gated with the gate pulse waveform 20a to remove only the pulse noise portion, and the gate output waveform 21a is It has gained.

Then, the de-emphasis circuit 22 integrates the gate output waveform 21a, shapes it into a rounded waveform, restores the characteristics of the audio signal, and outputs an output waveform 22a.

Here, the diagram showing the enlarged output waveforms 21a and 22a is waveforms 21b and 22b, and after all,
An audio output signal 22b from which pulse noise has been removed is outputted via the output stage 9, and this signal 22b is outputted from the speaker 10 as audio.

However, in some cases, even if the pulse noise disturbance has disappeared, the disturbance may be perceived as a partial level change in the audio signal.

Therefore, in the pulse shaping circuit 20, the gate pulse waveform 20a is changed to the waveform 11b in FIG.
The waveform is shaped and generated so that the rise and fall are gentle as shown in the figure, and this is used as the output waveform.

Therefore, the audio signal processing circuit 21 controls the gain of the output of the discriminator 17, that is, the audio signal 17a, using the waveform-shaped output waveform. This makes it possible to obtain the same effects as in the first embodiment described above.

[Effects of the invention] As described above, according to the invention, it is possible to simplify the circuit configuration, remove the pulse noise of the audio signal containing noise, and reduce the slope of the transient part by removing the noise of the signal. This has the effect of making it gentler so that the click sound is not perceived by the listener.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the pulse noise removing device according to the present invention, FIG. 2 is a waveform diagram output from each part shown in FIG. 1, and FIG. 3 is a diagram of the pulse noise removing device according to the present invention. A block diagram showing another example, Fig. 4 is a waveform diagram output from each part shown in Fig. 3, Fig. 5 is a waveform diagram showing the principle of perceiving click sound, and Fig. 6 is a conventional pulse noise diagram. FIG. 7 is a block diagram showing an example of the removing device, and is a waveform diagram of the output from each part shown in FIG. 6. 2... Intermediate frequency converter, 5... Switch pulse generation circuit, 4, 7... Detection circuit, 11... Low pass filter & waveform shaping circuit, 30... Low pass filter, 32... Waveform shaping circuit , 12... Delay circuit, 13... Gain control circuit, 20... Pulse shaping circuit, 21... Audio signal processing circuit.

Claims (1)

[Claims for Utility Model Registration] Receiving means for inputting a received signal, detecting the signal, and outputting a detected signal; and noise for detecting pulsed noise contained in the signal from the detected signal and outputting a noise signal. a detection means; a waveform shaping means for extracting a low frequency component of the noise signal and obtaining a waveform shaped signal subjected to waveform shaping processing such that the transient slope of the low frequency component becomes gentle with a predetermined pulse width; delay means for inputting a signal, delaying the detected signal by a predetermined time so that the noise signal included in the signal exists within the pulse width of the waveform shaping signal, and outputting the delayed detected signal as a delayed detected signal; A pulse noise removal device for a receiver, comprising: gain control means for controlling gain using a shaped signal.