JPH0447800A - Howling detector - Google Patents

Abstract

PURPOSE:To realize the howling detector with small hardware scale, low cost and high detection accuracy by calculating a short period average of an absolute value of the output of a differential arithmetic means and comparing it with a predetermined threshold so as to detect howling. CONSTITUTION:A binary means 2 converts an input signal 1 into a zero cross signal, a multiplier means 4 and a 1st delay means 3 obtain a zero cross point and a zero cross period detection means 5 detects the zero cross period. Then a time change in the zero cross period is calculated by a differential means 7 and an average value calculation means 8 calculates its short period mean value. That is, it is utilized that an output of the average value calculation means is very small in the case of a signal of a prescribed period such as howling to allow a howling detection means detects howling. Thus, the detector is realized with less calculation quantity and a simple hardware.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a howling detection device used in a system that causes rehearsal by a feedback loop, such as a public address system, a remote conference system, and a public address telephone.

Conventional technology In recent years, in addition to lectures and conferences, systems that apply public address equipment, such as remote conference systems and loudspeaker telephones, have been developed.
Sufficient volume, clear and natural voice transmission is desired. However, in reality, there is a risk of howling occurring, so the loudspeaker volume can be raised sufficiently.
The clarity and naturalness are not sufficient. Research on howling detection has been carried out in the past, and attempts have been made to detect howling by frequency analysis and adjust gain for each frequency based on the analysis results to obtain the maximum amount of amplification. (Japanese Patent Publication No. 59-94994 > The conventional howling detection device mentioned above will be explained below with reference to the drawings. Fig. 8 is a block diagram showing the configuration of a public address system incorporating the conventional howling detection device. 8, 101 is a micropon, 102 is a delay means for delaying the micropon signal for an arbitrary time, 110 is a howling detection device, 111 is a first band-pass filter group that performs frequency analysis of the output signal of the microphone, 112
113 is an average energy measurement circuit that detects the average energy of each band; 113 is a control circuit that detects howling from the average energy of each band and determines the gain amount of each band; 10
3 is a second bandpass filter group corresponding to the first bandpass filter group 111.
104 is an attenuator corresponding to each band of the second band-pass filter group 103, and control circuit 1
13 determines the amount of attenuation. 105 is an adder that adds each output of the attenuator 104;

The operation of the public address system incorporating the howling detection device configured as described above will be described below.

The speaker's voice is collected by a microphone 101 and divided into bands by a first band-pass filter group 111, and the energy of each band is measured by an average energy measuring circuit. The control circuit 113 takes advantage of the fact that howling is a pure tone and has an extremely narrow band compared to voice, and compares the energy of each band to determine whether the average energy of a particular band is larger than other bands. Detects when howling occurs. An attenuator corresponding to a band in which howling occurs is controlled to attenuate by a predetermined amount. Delay means 1
By using 02, the occurrence of howling can be detected earlier by the delay time.

Problems to be Solved by the Invention However, the conventional howling detection device described above requires a large number of bandpass filters to perform frequency analysis, and requires large hardware. Furthermore, in order to improve detection accuracy, it is necessary to increase the number of bandpass filters and narrow the bandwidth of each band, which further increases the hardware scale.

The present invention solves the above-mentioned conventional problems, and aims to provide a howling detection device that has a small hardware scale, can be realized at low cost, and has high detection accuracy.

Means for Solving the Problems In order to solve the above problems, the howling detection device of the present invention provides a method for detecting howling when the digital value of a digital signal obtained by converting an analog signal at a constant sampling period is 1 or more.
, a binarizing means for outputting -1 when the value is less than zero, a first delaying means for delaying the output of the binarizing means by one sample, and an output of the first delaying means and the binarizing means. a multiplication means for multiplying the output of , and an output of the multiplication means is -1
a zero-crossing period detection means that outputs the value counted at the time of , and also clears the counted value to zero; and a zero-crossing period that is the output of the zero-crossing period detection means, which is delayed by one zero-crossing period. a second delay means for calculating the difference between the output of the zero-crossing period detection means and the output of the second delay means; and a short-time average value of the absolute value of the output of the difference calculation means. The apparatus includes an average value calculating means for calculating, and a howling detecting means for detecting howling by comparing the output of the average value calculating means with a predetermined threshold value.

Furthermore, in addition to the above-mentioned configuration, the howling detection device of the present invention has the following features when the howling detection means detects howling:
and a howling frequency calculating means for calculating a howling frequency from the zero crossing period detected by the zero crossing detecting means.

Furthermore, the howling detection device of the present invention detects N digital signals (N is an integer of N≧1) during one sample period using a digital output sequence of a digital signal converted from an analog signal at a constant sampling period. an interpolating means for interpolating and outputting N+1 digital signals in one sample period; a binarizing means for outputting 1 when the output of the interpolating means is greater than or equal to zero; and -1 when the output is less than zero; and the binarizing means. a first delay means for delaying the output of by one signal <1/(N+1> samples), a multiplication means for multiplying the output of the first delay means and the output of the binarization means, and the multiplication means a zero-crossing period detection means that outputs the value counted when the output of the zero-crossing period is -1 and clears the counted value to zero; and zero-crossing period which is the output of the zero-crossing period detection means a second delay means for delaying by one crossing period; a difference calculation means for calculating the difference between the output of the zero crossing period detection means and the output of the second delay means; The apparatus includes an average value calculation means for calculating a short-time average value, and a howling detection means for detecting howling by comparing the output of the average value calculation means with a predetermined threshold value.

Furthermore, the interpolation means in the howling detection device of the present invention includes a third delay means that delays the digital signal by one sample, and calculates N values by linear interpolation from the digital signal and the output of the third delay means. It consists of a linear interpolation calculation means and outputs N+1 digital signals during one sample.

Operation With the above configuration, the input signal is converted into a zero-crossing signal by the binarization means, the zero-crossing point is determined by the multiplication means and the first delaying means, the zero-crossing period is detected by the zero-crossing period detection stage f,
By calculating the time change of the zero crossing period by the difference means and calculating the short-term average value by the average value calculation means, the output of the average value calculation means can be extremely small in the case of a signal with a constant period such as howling. Howling can be detected using a howling detection means. Furthermore, when howling is detected, the howling frequency is determined by the howling frequency detection means from the zero-crossing period detected by the zero-crossing period detection means.

Furthermore, the interpolation means interpolates N digital signals during one sample interval using the digital output series.
Since N[-1 digital signals are output in each sample period, the resolution of the zero-crossing period detected by the zero-crossing period detecting means is improved, and the output width of the difference means can be increased, making it possible to reduce noise in speech and noise. Malfunctions are reduced, and the threshold value can be increased, which improves howling detection speed.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a howling detection device in a first embodiment of the present invention. In Figure 1,
2 is '1' when the digital output X of the analog-to-digital conversion means 1 is greater than or equal to zero;
, when less than , "I t, Binarization means to convert to TT, 3 is the output l of the binarization means] A first delay means that delays the output l by one sample, 4 is the output of the binarization means 2 A multiplier that multiplies b by the output b of the first delay means and detects a zero crossing point. A zero-crossing period detecting means detects a zero-crossing period by clearing the count value to zero after outputting the value of the counter when . 7 is a difference means for subtracting the output Dj-1 of the second delay means 6 from the output D of the zero-crossing period detection means 5 and outputs the difference value ΔDj of the zero-crossing period; 8 is the output of the difference means 7 ΔD
A value calculation means 9 compares the output A of the average value calculation means 8 with a predetermined threshold value, and outputs the short-term average giA of the absolute value of , Howling detection stage 1 determines howling when the output is smaller than a threshold, and 10 indicates howling frequency from the zero crossing period detected by zero crossing period detecting means 5 when howling detecting first stage 9 detects howling. This is a howling frequency calculation means for calculating.

Regarding the howling detection device configured as above,
Below, we will explain its operation.

FIG. 2 is a diagram showing the operating principle of the howling detection device in the case of voice or noise. As shown in FIG. 2(a), the input signal W
is converted into digital signal X by analog-to-digital converter 1
is converted to In FIG. 2(b), the digital output X by the binarization means 2 is "]" when it is less than zero or -1-.
, is converted to a binary code b of '1' when it is less than zero.Furthermore, in FIG.
is the binary signal delayed by one sample by the first delay means 3, and the multiplication is combined by the multiplication means 4. The output CJb, *b, 1 of the multiplication means 4 takes a value of "1" or "-1'". -1'' when b and bj-1 have different signs, and J-i between samples b and b
J A zero crossing is taking place. In FIG. 2(d), the zero-crossing period detection means 5 counts up the number of samples from when the multiplication output C0 becomes "I II" until it becomes -1 (marked by ■ in FIG. 2(d)). Then, the zero crossing period is detected. Furthermore, in FIG. 2(e), the difference means 7 calculates the zero-crossing period Dj currently detected by the zero-crossing period detecting means 5 from the previous zero-crossing period Dj-1 outputted from the second delay means 6. The subtraction (D, -D,) and the difference value J-I J ΔD of the zero-crossing period are output. In FIG. 2(f), the average value calculation means 8 takes the absolute value ΔD 1 of the output ΔDJ of the difference means 7 and outputs the short-time force value A having the absolute value 1 ΔDJ l. In addition, in this case, as shown in FIG. 2(f) when howling is detected, the value A calculated by the average value calculation means 8 is larger than the threshold value B, which indicates that the input signal is not howling. .

FIG. 3 shows a diagram of the operating principle when howling occurs.

Figure 3 (a), (b), (C), (dL (e)
, (f) are respectively 211r (a), [b),
(c), (d), (e), if). When howling is input, the output DJ of the zero crossing period detection means 5 in FIG. 3(d) becomes constant V1, and furthermore, the output of the difference means 7 in FIG. 31(C) becomes zero. . As shown in FIG. 3(f), the output A of the average value calculating means 8 becomes almost zero and is smaller than the threshold value B, and it is detected that howling is occurring. Actually, the amplitude of the difference means 7 does not become completely zero because noise is superimposed on the howling sine wave. Therefore, a value of about 1.2 is used as the threshold value B so as to avoid erroneously detecting noise as howling and to reduce the probability of erroneously detecting voice. When it is determined that howling has occurred, the howling frequency calculating means 10 calculates the howling frequency Fhi according to the following equation using the zero crossing period Dj detected by the zero crossing period detecting means.

FhJ-] / (2*D J* T S )'I゛:
As described above, according to the first embodiment, the analog-to-digital converter 1, the binarization means 2, the first and second delay means 3 and 6, the multiplication means 4, and the zero-crossing period detection means 5. The howling system is composed of a difference means 7, an average value calculation means 8, a howling detection means 9, and a howling frequency detection means 10, and requires less calculations compared to a configuration using a conventional filter group, and can be configured with simple hardware. It can be a detector.

Note that an analog-to-digital converter is not required when the input signal is obtained as a digital signal.

If the analog-to-digital converter 1 and the binarization means 2 are combined into a binary analog-to-digital converter, the hardware becomes even smaller.

Next, a second embodiment will be described with reference to the drawings. FIG. 4 is a block diagram showing the configuration of a howling detection device in a second embodiment of the present invention. In FIG. 4, 1 is an analog-to-digital conversion means for converting the input signal W from analog to digital, and 2 is the digital output of the interpolation means 20, which is '1' when the value is less than -E, and '1' when it is less than -1. 3 is a first delay means, 4 is a multiplication means, 5 is a zero-crossing period detection means, 6 is a second
, 7 is a difference means, 8 is an average value calculation means, 9 is a howling detection means, and 10 is a howling frequency calculation means, which are the same as those in the first embodiment. 20
1 is an interpolation means that interpolates one digital signal during one sample period using the digital output series of the analog digital converter 1, and outputs two digital signals in the sampling period. FIG. 5 shows details of the interpolation means.

21 is a third delay means for delaying the output X of the analog-to-digital converter 1 by one sample; 22 is a third delay means for delaying the output X of the analog-to-digital converter 1 by one sample; and 22 is the output of the analog-to-digital converter 1, This is a linear interpolation calculation means that calculates the average value of both.

Regarding the howling detection device configured as above,
The operation will be explained below. FIG. 6 is a diagram showing the operating principle of the howling detection device when no howling is occurring.

As shown in FIG. 6(a), the input signal W is converted by the analog-to-digital converter 1 into a digital signal X (indicated by ■). Further, FIG. 6(a) shows the output X of the analog-to-digital converter 1 delayed by one sample by the third delay means 21, and the digital output X by the linear interpolation means 22.
The average value ((Xj-1+xj)/2) with j is calculated,
This shows that one signal X (mark) is interpolated by j-1 in one sample period. Below, Figure 6(b)
, (c), (d), (e), (f) respectively correspond to Figure 2 (bL (c) (d), fe), ff), or the difference means in Figure 6 (e). Since the amplitude width of the output signal ΔDj of the previous item 7 is about twice the amplitude width of the output signal ΔDJ of the difference means 7 in FIG. 2(e),
), the output of the average value calculation means 8 is approximately twice as large as that in FIG. 2(f), and the difference with the threshold value B is large.

FIG. 7 shows a diagram of the operating principle of the howling detection device when howling occurs. Figure 7(a)(b), (
cL (d) and (eL ke) are respectively shown in Fig. 6 (a),
(b) fcL Corresponds to (d), (e), and (f). When howling is input, the output Dj of the zero-crossing period detection Hf stage 5 in FIG. 7(d) becomes a constant value, and the
The output ΔDJ of the difference means 7 in Figure (e) is zero.

As shown in FIG. 7(f), the output A of the average value calculation means 8
becomes almost zero and is smaller than the threshold value B, and it is detected that howling is occurring. These operations are similar to those in the first embodiment.

Howling frequency calculation means 10 determines that howling has occurred (1!)! Howling frequency F'hJ is calculated according to the following formula using the zero-crossing period D detected by the zero-crossing period detecting means 5 when the zero-crossing period is detected. The operation is similar to the first embodiment.

F,,=1/(2*D,*′l”,)TS
:→ Re-sampling period As described above, in the second embodiment, the interpolation means 20 is provided after the analog-to-digital conversion means 1 of the first embodiment, and the zero-crossing period detected by the zero-crossing period detecting means 5 By improving the resolution of Dj, the output width of the difference means 7 when voice or noise is input can be approximately doubled, and malfunctions due to voice or noise can be reduced.

In addition, by increasing the threshold value B from a value of about 1.2 in the first embodiment to a value of about <1.8, the howling detection speed can be improved and howling can be detected quickly. . Linear interpolation means 22 as interpolation means 20
By using this, the increase in hardware (amount of calculation) is due to the need for one delay means 21, linear interpolation means 22 for calculating the average value of two signals, multiplication means 4, zero crossing period detection The number of calculations of the means 5, the difference means 7, and the average value calculation means 8 is approximately doubled, and the amount of calculations is smaller compared to a configuration using a conventional filter group, and it can be configured with simple hardware. Compared to the embodiment, performance can be improved by reducing malfunctions and improving howling detection speed.

Note that if the input signal W is obtained as a digital signal, the analog-to-digital converter 1 is not necessary.

Furthermore, in the second embodiment, one signal is interpolated between sample values, but by interpolating more signals, the howling detection speed is improved and the probability of malfunction during voice input is reduced.

Effects of the Invention - F.31 According to the present invention, a howling detector that requires less calculation than a configuration using a conventional filter group and can be configured with simple hardware can be obtained. Furthermore, by setting the interpolation means and improving the resolution of the zero crossing period detected by the zero crossing period detecting means at Ct,
It is possible to increase the output width of the difference means when voice or noise is input, reducing malfunctions due to voice or noise, and by providing an interpolation means, the threshold value can be increased to detect howling. Increase speed and eliminate howling [? −<Can be detected.

[Brief explanation of drawings]

FIG. 1 shows the configuration of the howling detection device according to the first embodiment of the present invention.
), FC), fd), (e), (f) are output signal waveform diagrams of each means to explain the operating principle when voice or noise is input to the howling device, Figure 3 fa)
(b), (c), (d), (e), and (f) are output signal waveform diagrams of each means to explain the operating principle when a howling signal is input to the howling detection device, and FIG. A block diagram showing the configuration of the howling detection device in the second embodiment of the present invention, FIG. 5 does not show the configuration of the interpolation means in the howling device.
, (b), (c), (d), (eL (f) is an output signal waveform diagram of each means to explain the operating principle when voice or noise is input to the howling detection device, FIG. a). (b), (cL (d), fe), (f) are output signal waveform diagrams of each means to explain the operating principle when a howling signal is input to the howling detection device, and FIG. It is a block diagram showing the structure of the public address system which introduced the conventional howling detection device. 2... Binarization means, 3... First delay means, 4...
- Multiplying means, 5... Zero crossing period detection means, 6... Second delay means, 7... Differential means, 8... Average value calculation means, 9... Howling detection means, 10... - Howling frequency calculation means, 20... Interpolation means, 21... Third delay means, ... Linear interpolation means.

Claims (1)

[Claims] 1. 1 when the digital value of the digital signal obtained by converting the analog signal at a constant sampling period is greater than or equal to zero;
, a binarizing means for outputting -1 when the value is less than zero, a first delaying means for delaying the output of the binarizing means by one sample, and an output of the first delaying means and the binarizing means. a multiplication means for multiplying the output of , and an output of the multiplication means is -1
a zero-crossing period detection means that outputs the value counted at the time of , and also clears the counted value to zero; and a zero-crossing period that is the output of the zero-crossing period detection means, which is delayed by one zero-crossing period. a second delay means for calculating the difference between the output of the zero-crossing period detection means and the output of the second delay means; and a short-time average value of the absolute value of the output of the difference calculation means. A howling detection device comprising an average value calculation means for calculating, and a howling detection means for detecting howling by comparing the output of the average value calculation means with a predetermined threshold value. 2. 1 when the digital value of the digital signal obtained by converting the analog signal at a constant sampling period is greater than or equal to zero.
, a binarizing means for outputting -1 when the value is less than zero, a first delaying means for delaying the output of the binarizing means by one sample, and an output of the first delaying means and the binarizing means. a multiplication means for multiplying the output of , and an output of the multiplication means is -1
zero-crossing period detection means for outputting the value counted at the time and clearing the counted value to zero; and delaying the zero-crossing period, which is the output of the zero-crossing period detection means, by one zero-crossing period. a second delay means; a difference calculation means for calculating the difference between the output of the zero-crossing period detection means and the output of the second delay means; and a short-time average value of the absolute value of the output of the difference calculation means. an average value calculation means for detecting howling by comparing the output of the average value calculation means with a predetermined threshold; and a howling detection means for detecting howling by comparing the output of the average value calculation means with a predetermined threshold; A howling detection device comprising: howling frequency calculation means for calculating a howling frequency from a zero crossing period detected by the detection means. 3. Interpolate N digital signals (N is an integer of N≧1) during one sample period using a digital output sequence of a digital signal obtained by converting an analog signal at a constant sampling period, and interpolate N+1 digital signals during one sample period. interpolation means that outputs 1 digital signal; binarization means that outputs 1 when the output of the interpolation means is greater than or equal to zero; and -1 when it is less than zero; 1/(N+
1) a first delay means for delaying (by sample); a multiplication means for multiplying the output of the first delay means by the output of the binarization means; and a count when the output of the multiplication means is -1. a zero-crossing period detection means for outputting the counted value and clearing the counted value to zero; and a second delay for delaying the zero-crossing period, which is the output of the zero-crossing period detection means, by one zero-crossing period. means, a difference calculation means for calculating the difference between the output of the zero-crossing period detection means and the output of the second delay means, and an average value calculation for calculating a short-term average value of the absolute value of the output of the difference calculation means. and howling detection means for detecting howling by comparing the output of the average value calculation means with a predetermined threshold. 4. The interpolation means includes a third delay means that delays the digital signal by one sample, and a linear interpolation calculation means that calculates N values from the digital signal and the output of the third delay means by linear interpolation. and N during one sample.
4. The howling detection device according to claim 3, wherein the howling detection device outputs +1 digital signals.