Patent ID: 7840014

Claim:
A single-unit acoustic system comprising: input means with which an audio signal is input; conversion means that converts the audio signal from the input means into a digital signal; a howling prevention system comprising a digital filter which reduces an output level of a specific frequency component of the digital signal converted by the conversion means; and an amplification system that amplifies the audio signal after the howling prevention systems changes frequency characteristics of said audio signal; sound source means generating an audio signal at a specified sampling period, wherein the generated audio signal comprises some sample points having a series of non-zero amplitude values and some sample points with amplitude values made at 0 between adjacent sample points with the series of non-zero amplitude values; and output means outputting the audio signal generated by the sound source means into space; wherein the input means inputs the audio signal outputted by the output means, and the digital filter reducing the output level of the frequency designated by the frequency designation means; wherein the howling prevention system further comprises: frequency characteristics detection means that detects frequency characteristics of the audio signal inputted by the input means; and frequency designation means that designates a frequency based on the frequency characteristics detected by the frequency characteristics detection means; wherein the digital filter reduces the output level of the frequency designated by the frequency designation means; and wherein in the sound source means further comprises: waveform storage means storing a series of amplitude values in which specified waveforms have been sampled at a specified sampling period; amplitude value readout means reading out successive amplitude values from the waveform storage means; and sample point addition means adding the sample points between the adjacent amplitude values read out by the amplitude value readout means at a specified sampling period, wherein amplitude values of the sample points added are made 0.