| 摘要 |
<p>PURPOSE:To prevent the howling, by delaying the band signals divided into plural bands by a certain period of time, measuring the mean energy of the band signal with every certain time and comparing the mean energy with the threshold value to control the degree of attenuation. CONSTITUTION:The signal supplied through an input terminal 100 is divided for the band by (n) units of band filters 20(1-n) and led to a delay circuit 30(1-n) to be delayed by a certain time. At the same time, the signal is led to mean energy measuring circuits 60(1-n) to obtain mean energies W1-Wn with every certain time. These energies are compared 70(1-n) with the threshold value WO. The comparators 70(1-n) supply a signal (1) to variable attenuators 40 (1-n) in the case of W1-Wn>WO to carry out a certain attenuation beta. The attenuator 40 contains the control signal holding function and the multiplying function and holds the degree of attenuation until the next input signal and then revises the degree of attenuation with a new input. The outputs of the attenuators 40 are added 500 to obtain an output 800. In such way, the howling can be automatically prevented without lowering the sound quality.</p> |
