| 摘要 |
PURPOSE:To effectively reject impulse noises without much damage to an original signal, by changing a cutoff frequency of a variable filter added with the original signal in accordance with the duration time of the impulse noises. CONSTITUTION:A music signal having an impulse noise from an input terminal is applied to a voltage controlled type LPF filter 12 via signal delay circuit 11. On the other hand, the impulse noise component included in the said music signal is detected at a noise detecting circuit 13 and it is converted into a pulse width signal having a pulse width corresponding to the duration time at a pulse forming circuit 14. Further, this pulse width signal is converted into a DC voltage corresponding to the pulse width at a pulse width/voltage converting circuit 15 and applied to a control terminal of the said voltage variable type LPF filter 12. Thus, if the duration time of impulse noise is short, the cutoff frequency of the LPF filter 12 is higher and inversely, if the duration time of the impulse noise is longer, the cutoff frequency becomes lower. |
