| 摘要 |
PURPOSE:To eliminate the noises generated by the discontinuous part of the signal which is generated at the time of switching by using a prescribed frequency to open and close a switch which extracts an output signal selectively out of those of plural transmission systems. CONSTITUTION:The audio signals obtained from the signals which are reproduced alternately for every cycle of about 30Hz are delivered from terminals 1 and 2 through switches 3 and 4 and an LPF5. An oscillator 6 oscillates a clock pulse Pc of a frequency (f1=100kHz) for example. At the same time, a switching pulse Ps of 30Hz is supplied to a terminal 7. The rise of the pulse Pc is detected and applied to NAND gates 8 and 9, while the fall of the pulse Pc is detected to set FFs 10 and 11 respectively. In such a way, the switch 4 is opened and closed with an output Q1 given from the FF10, and the switch 3 is opened and closed with an output Q2 given from the FF11. Then the audio signal is substantially converted into a band at the outside of the audible bands centering on f1 in terms of frequency. Thus the noises of audible bands due to the signal discontinuous part are driven to the outside of the audible bands. |
