| 摘要 |
PURPOSE:To prevent howling with the hardware of a small scale by changing the transmission characteristics of a band eliminate filter with the combination of a phase-shifting circuit and a phase comparator and allowing the peak frequency whose amplification rate is decreased to follow the frequency generating the howling. CONSTITUTION:Two kind to signals whose frequency and intensity are almost constant and whose phase difference is different correspondingly with the frequency, a voice signal 121, and a phase-shifting voice signal 141 are conducted into a phase comparator 15 through its comparison input. The phase comparator 15 outputs voltage corresponding to the phase difference of two kind of signals conducted by the comparison input. The voltage is conducted by a voltage storage circuit 16 and sent out to a band eliminate filter 13 after the delay of the time of time constant. When the frequency generating the howling is f1, the frequency characteristics of amplification series from a microphone 11 to a loud speaker 18 becomes the characteristics whose amplification rate is decreased only at the frequency of f1. Thus, voice generating the howling is no longer reproduced from the loud speaker 18. |
