JPH0444480B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a device for suppressing howling in a public address system composed of a microphone, an amplifier, a speaker, and the like.

Configuration of conventional example and its problems FIG. 1 shows a block diagram of a conventional howling suppression device. The signal input to the input terminal 1 is branched into two, and one of the branched signals is delayed by a delay circuit 2 and then input to a plurality of band pass filters 3 to 5, where it is frequency-divided. The signals are input to attenuators 13 to 15 corresponding to each band. The other branched signal is similarly input to a plurality of bandpass filters 6 to 8, frequency-divided by these, and average energy measuring circuits 9 to 8.
11, and its output is input to a control circuit 12 which compares the average energy level and controls the amount of attenuation of attenuators 13-15. The outputs of the attenuators 13 to 15 controlled by the control circuit 12 are added by the adding circuit 16 and output from the output terminal 17, thereby suppressing howling. Since this device includes a delay circuit 2, the processing time for howling is delayed, and passing through this delay circuit 2 degrades the original signal. Further, two band filters 3 to 5 and two band filters 6 to 8, which are similar to those for original signals and for howling detection, are required, respectively, resulting in an increase in the number of parts and a complicated circuit configuration.

OBJECTS OF THE INVENTION An object of the present invention is to overcome the drawbacks of the conventional howling suppression devices described above and to provide an adaptive howling device that can suppress howling in any situation.

Configuration of the invention The configuration of the present invention is such that in a conference room, hall, etc.
In an acoustic system in which the voice of a speaker is collected by a microphone, and the voice is amplified by an amplifier and a speaker in the same sound field as the microphone, the microphone is inserted into the electrical system from the loudspeaker amplifier to the speaker, and multiple band filters are used. have,
This howling suppression device is configured to detect a band where howling occurs and suppress the filter output of the band where howling occurs using an attenuator.

DESCRIPTION OF EMBODIMENTS The present invention will be described below with reference to FIG. 2 of the embodiment. The signal input to the input terminal 18 is input to a plurality of band pass filters 19 to 21, frequency division is performed by these, and the signal is input to the band pass filter 1.
The outputs of 9 to 21 are branched into two. One of the two branched signals is input to attenuators 26-28, and the other branched signal is input to average energy measuring circuits 22-24. The average energy of each band signal determined by the average energy measurement circuits 22 to 24 is input to the control circuit 25. This control circuit 25 calculates the level difference between the average energy of each band before and after that band, detects the occurrence of howling based on the amount of the difference, and controls the amount of attenuation of the attenuators 26 to 28. do. The outputs of the attenuators 26 to 28 are sent to an adder circuit 29
are added and output from the output terminal 30.

FIG. 3 shows howling frequency characteristics showing howling margin improvement when using the device of the present invention.

In Fig. 3, the solid line is the through frequency (when no howling processing is performed), the broken line is the howling frequency when the howling suppression amount (attenuation amount of the attenuator) is 3 dB, and the dashed line is the howling frequency when the howling suppression amount is 6 dB. It is a characteristic. This figure shows that by using the device of the present invention, the howling margin was improved by 5 dB when the amount of howling suppression was 3 dB, and by 9 dB when the amount of howling suppression was 6 dB.
In this case, the method of detecting howling in the control circuit 25 is to simply calculate the difference in the average energy of one band at a certain point in time, and calculate the difference as the average energy of each of the normal (when no howling occurs) audio signals. There is a method in which it is considered howling when the level difference is greater than the level difference in the audio signal, and a method in which this comparison is made for a certain period of time, and if the level difference continuously exceeds the level difference in the case of an audio signal during that period, it is considered as howling. When comparing the average energy, a method may be considered in which this comparison is performed only when the average energy of the band of interest monotonically increases within a certain period of time.

Effects of the Invention As detailed above, the present invention eliminates delay in the original signal, reduces the number of filters, divides the input signal into multiple frequencies, and compares the average energy level of each divided signal. This makes it possible to provide a howling suppression device that can quickly detect and suppress the occurrence of howling.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram showing a conventional howling suppression device, Fig. 2 is a block circuit diagram showing an embodiment of the howling suppression device of the present invention, and Fig. 3 shows howling when the device of the present invention is actually used. FIG. 3 is a characteristic diagram showing improvement in margin. 18...Input terminal, 19-21...Band pass filter, 22-24...Average energy measuring circuit, 25...
Control circuit, 26-28...attenuator, 29...addition circuit, 30...output terminal.

Claims (1)

[Claims] 1 Band division means for dividing an input signal into a plurality of frequency bands; each signal divided by the plurality of band division means is branched into two, and one of the divided signals is divided into two. The attenuation amount of the attenuation means is controlled by comparing the level of the average energy measured by the attenuation means that attenuates by an arbitrary amount and the average energy measurement means that measures the average energy of each of the other branched divided signals. and an addition means that adds the output signals of the attenuation means, and the control means compares the average energy in one band with the average energy in the bands before and after it, and calculates the average energy. A howling suppression device that is a control means that controls the amount of attenuation of an attenuator corresponding to a band when the difference in energy is larger than the difference in average energy of each band in a normal audio signal. 2 The control means detects the average energy of each band at certain fixed time intervals, compares the average energy of one band with the average energy of the bands before and after it, and detects the average energy of each band continuously for a certain period of time during which there is a difference in the average energy. 2. The howling suppression device according to claim 1, wherein when the difference in average energy of each band is greater than the difference in average energy of each band in a normal audio signal, the attenuation amount of the attenuator corresponding to that band is controlled. 3. The control means compares the average energy in one band with the average energy in the bands before and after it, and performs the comparison only when the average energy in the band increases continuously for a certain period of time. The howling suppression device according to item 1.