Electrical audio signal processing systems and devices – Including frequency control – Having automatic equalizer circuit
Reexamination Certificate
1997-11-12
2001-06-26
Harvey, Minsun Oh (Department: 2644)
Electrical audio signal processing systems and devices
Including frequency control
Having automatic equalizer circuit
C381S083000, C381S093000
Reexamination Certificate
active
06252969
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a howling detection and prevention circuit and a loudspeaker system employing this circuit.
In radiating an acoustic power using a microphone and a loudspeaker, a loud sound produced by the loudspeker is sometimes accompanied by howling. For preventing howling, it is conceivable to increase entire gain of radiation of an acoustic power in which howling is produced by restraining the entire gain of radiation of acoustic power to a level which is below a level at which howling is produced or reduce the gain of a frequency region in which howling starts to take place. In the past, for preventing howling, a user manipulates a volume control while confirming presence or absence of howling to set the entire gain of radiation of acoustic power to a level at which howling is not produced or sets the entire gain after decreasing the gain of a particular frequency region by using a graphic equalizer or a notch filter. Adjustment of the gain is made relying upon the user's hearing. Once howling has occurred, the user usually hurries to the loudspeaker system and stops howling by lowering the volume level. In such a case, it takes time before howling stops and the user cannot avoid unpleasantness caused by howling during this time.
Thus, manual adjustment of the gain for preventing occurrence of howling in the prior art loudspeaker system has caused the problems of lack in accuracy and stability, requirement for the troublesome adjustment and requirement for time for adjustment.
It is, therefore, an object of the invention to provide a howling detection and prevention circuit capable of automatically detecting and preventing howling and a loudspeaker system employing the same circuit.
SUMMARY OF THE INVENTION
For achieving the above described object of the invention, there is provided a howling detection and prevention circuit which receives an output of a microphone as its input signal and detects howling therein comprising a computing section which divides frequency of the input signal into a plurality of frequency bands on the basis of a predetermined sampling period and computes power of each of the frequency bands, an identifying section which sequentially shifts the frequency band and identifies whether howling exists or not in accordance with a predetermined condition by employing value of the computed power of each frequency band, and a gain adjusting section which, when howling has been detected as a result of the identifying, adjusts gain of the frequency band in which the howling has been detected to prevent the howling.
According to the invention, an input signal is divided into frequency bands and thereafter power of each frequency band is computed. The condition of howling is searched by sequentially changing the frequency band and, when there is a frequency band which satisfies the howling condition, this band is detected as a howling frequency band and prevention of howling is performed. By this arrangement, in a loudspeaker system and a PA (public address) system using a microphone, howling which occurs when sound volume is raised above a certain value can be automatically detected. When howling has been detected, the howling can be prevented by automatically adjusting gain of the frequency band. Accordingly, howling can be automatically prevented without requiring a user's manipulation.
In one aspect of the invention, the howling detection and prevention circuit further comprises an entire gain adjusting section which adjusts entire gain of all of the frequency bands in accordance with the result of the identifying by the identifying section to prevent the howling.
In another aspect of the invention, said computing section computes power of each frequency band by computing moving averages with respect to each of the frequency bands which has been provided by frequency division on the basis of the predetermined sampling period.
In another aspect of the invention, said identifying section identifies presence or absence of howling on the basis difference between an absolute value of a power in the frequency band under identifying and a power of the frequency band in the vicinity thereof.
In still another aspect of the invention, there is provided a loudspeaker system comprising a microphone, a howling detection and prevention circuit described above which receives a signal from the microphone as its input signal, an amplifying section which amplifies an output signal of the howling detection and prevention circuit, and a loudspeaker which is driven by an output of the amplifying section.
A preferred embodiment of the invention will be described below with reference to the accompanying drawings.
REFERENCES:
patent: 4783819 (1988-11-01), De Koning et al.
patent: 5442712 (1995-08-01), Kawamura et al.
patent: 5677987 (1997-10-01), Seki et al.
patent: 161995 (1984-09-01), None
patent: 60-126998 (1985-07-01), None
patent: 60-176313 (1985-09-01), None
J. Boudy, et al., “Hands-free Radiotelephones for car applications”, publication date Dec. 1, 1992, pp. 247-253.
Harvey Minsun Oh
Pillsbury & Winthrop LLP
Yamaha Corporation
LandOfFree
Howling detection and prevention circuit and a loudspeaker... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Howling detection and prevention circuit and a loudspeaker..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Howling detection and prevention circuit and a loudspeaker... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2469881