1. Technical Field
The present invention generally relates to a signal processing method of emphasizing a relatively high peak frequency component among a plurality of peak frequency components of a sound signal , and specifically relates to a method of acquiring frequency characteristics emphasizing a frequency component causing howling (hereafter referred to as a “howling frequency component”) and its apparatus in order to contribute to improvement of the precision for distinction between the sound signal and howling noise. Further, the present invention relates to a method of detecting howling by using the howling frequency component emphasis method and its apparatus. Moreover, the present invention relates to a method of suppressing howling by using the howling detection method and its apparatus.
2. Related Art
There is known a sound amplification system so configured that a microphone and a speaker is arranged in a space such as a hall, and the speaker amplifies the sound picked up by the speaker. In such system, the microphone re-picks up the sound amplified by the speaker to make up a so-called acoustic feedback system, and possibly cause howling. Conventionally, there has been available a technique to suppress howling in the acoustic feedback system. Such technique always applies frequency analysis to a sound signal collected by a microphone, then detects a peak frequency having the maximum amplitude, and decreases a gain of the detected peak frequency.
The following patent documents describe the prior art of detecting howling frequencies in an acoustic feedback system and decreasing a gain of the detected peak frequency to suppress the howling.
[Patent document 1] Patent Publication No. 3134557
[Patent document 2] Japanese Non-examined Patent Publication No. 8-223683
The conventional technique suppresses howling based on the simple peak detection. The technique cannot clearly distinguish between frequency peak components of the sound (such as a musical sound) and a howling peak until the howling grows up to a sufficient amplitude. It has been impossible to fast detect the howling before the howling reaches the maximal strength.