| 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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