| 摘要 |
PURPOSE:To remove an external noise to a signal concerning the operation of a control circuit by providing a filter for removing a frequency signal component approximately same as the frequency signal concerning the operation of the control circuit at the back stage of a michrophone head and at the front stage of the control circuit. CONSTITUTION:A noise signal detected in a dynamic michrophone head 1 is impressed to a notch filter 3 through a low frequency amplifier circuit 2. The notch filter 3 has a filtering characteristic attenuating the signal at a frequency band of 1-2kHz in the vicinity of a frequency 31.5kHz as a central frequency which is the double of the horizontally synchronizing signal of a television monitor. Therefore, even when the dynamic michrophone head 1 captures the noise signal in vicinity of 31.5KHz, an output signal from a circuit at the back stage of the notch filter 3, especially from a musical interval raising key control circuit 8, is not affected. |
