| 摘要 |
A noise canceling apparatus ( 1 ) comprises an amplifier ( 10 ) for amplifying a measured signal (ms) outputted from a measuring device ( 3 ), an analog filter ( 11 ), an ADC ( 12 ), a digital filter ( 14 ), a coefficient control section ( 13 ), and a data input section ( 15 ). The digital filter ( 14 ) is a notch filter for attenuating a frequency component of a quantitative signal D(n) outputted from the ADC ( 12 ) at a plurality of notches (stop bands). A transfer function of the digital filter ( 14 ) is expressed by the product of a plurality of factors each having a root that corresponds to each one of the plurality of notches. The coefficient control section ( 13 ) changes a frequency component of a root corresponding to a notch selected from the plurality of notches, and thereafter, expands in a polynomial the transfer function of the reconstructed digital filter ( 14 ). On the basis of the polynomial thereby obtained, a new series of filter coefficients is calculated. A filter characteristic is controlled in such a manner that it conforms to a frequency variation of a fixed-period vibration noise, whereby the fixed-period vibration noise that varies in frequency is attenuated with a high degree of precision.
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