| 摘要 |
PURPOSE:To improve the signal-to-noise S/N of sound and control signals, by providing the 2nd low-pass filter which outputs a detect signal when noises exceed a prescribed level and is provided in parallel with the 1st low-pass filter. CONSTITUTION:The S/N of the detector output signal drops and high-frequency noise level increases in a noise detecting circuit 6, when the wireless coupling between a slave wireless set and host wireless set becomes a weak electric field state. The noise components are extracted by a band-pass filter 6a and become DC signals after they are rectified by a rectifier circuit 6b, and them, are inputted to a comparator 6c where they are compared with a reference voltage. When the noise level increases and the voltage impressed across the comparator 6c exceeds the voltage generated by a reference voltage generator 14, the comparator 6c generates a control signal and turns on a switch 6d. As a result, a capacitor 9 is connected with a de-emphasis circuit composed of a resistance 7 and capacitor 8 and the time constant is raised and high-frequency noise components are damped. Accordingly, the S/N is improved. |
