| 摘要 |
<p>PURPOSE:To improve the degree of freedom in use by adopting the constitution such that an input section, an amplifier section having a variable gain amplifier function and an output section are used so as to attenuate in a very short period as to a signal being discontinuous and consecutive only for a short period thereby preventing howling. CONSTITUTION:A voice signal inputted from a microphone of an input section 1 is band-limited from 200Hz to 6kHz by a band limit circuit and reaches a variable gain amplifier section. The variable gain amplifier section has a characteristic not always being linear and changing periodically while being consecutive from an amplification factor of 0dB to 50dB at 15kHz-20kHz. The voice signal reaching the variable gain amplifier section is at a far low frequency band in comparison with the gain change of the amplifier and recognized as a voice signal as if the maximum amplification factor is constant to human ears. In general, howling is generated from a single frequency component of a very minute voltage among environmental noise in a system having a constant amplification factor in a time nearly 10msec and the howling is attenuated momentarily in the amplifier system and not recognized as the sound.</p> |
