| 摘要 |
When the frequency of an input sound signal applied to a shifting type echo-machine is close to that of the shift pulse thereof, a false signal appears at the output terminal of the echo-machine, in addition to the other type of noise signal caused by inclusion of the shift pulse component in the output of the same. The present invention is an echo-machine provided with first and second low pass filters, arranged before and after the delay element included in the echo-machine respectively, with a variable cut-off frequency which varies in accordance with the frequency of the shift pulse thereby eliminating such an erroneous signal and the shift pulse component from the output signal of the echo-machine. In its more specific aspects, the echo-machine is provided with low pass filters with a variable cut-off frequency employing an active filter containing one or more integrating circuit of which the input signal is interrupted in accordance with the frequency of a clock pulse to determine the cut-off frequency of the active filter. |
