| 摘要 |
PURPOSE:To reduce the discordant noise sound, by operating a filter by a switch circuit to attenuate high-band components of a stereo signal when the output of the stereo signal becomes a prescribed value or less. CONSTITUTION:A composite signal obtained from an FM detecting circuit is demodulated to left and right stereo signals in an FM multiplexer, 1 and they are taken out and are allowed to pass through LPFs 2 and 3 to eliminate the carrier leak, and these signals are outputted to terminals 4L and 4R through resistance R9 and R10. L and R components of stereo signals are amplified in amplifiers 5 and 6 and are given to transistors TRs Q1 and Q2, and a larger output is subjected to half-wave rectification selectively and is inputted to the + pole of a comparator 7. This output is compared with a prescribed level based on resistances R7 and R8 in the comparator 7; and when it is lower than the prescribed value, the output of the comparator 7 becomes L-level, and TRs Q3 and Q4 are turned off, and TRs Q5 and Q6 are turned on, and LPFs consisting of resistance R9 and R10 and capacitors C6 and C7 are operated, and high- band components of stereo signals are attenuated to reduce the noise sound. |
