| 摘要 |
PURPOSE:To correctly input sound without being affected with surrounding noise, by automatically adjusting the gain of a sound signal including the surrounding noise and keeping the result to an optimum value, through the signal level at a frequency region other than frequency components of the sound signal. CONSTITUTION:A sound signal detected at a sound detection microphone 1 is amplified at a preamplifier 2, and the sound frequency region only is inputted to an amplifying circuit 5 at a band-pass filter. A noise signal detected at a microhone 1' for noise detection is amplified at a preamplifier 2' and components other than the sound frequency region are inputted to a smoothing circuit 4 at a band block filter 3'. The amplification factor of the circuit 5 is adjusted in response to the output level of the circuit 4. An output L5 of the circuit 5 is compared with a threshold level LT at a signal processing circuit 6, and when L5>LT, the component is decided as that in the sound region. The output of the circuit 6 is inputted to a filter bank 7 to form an output pattern at each frequency, and decision is done through the pattern matching with the sound pattern registrated at a deciding circuit 8. |
