Patent ID: 7720646

Claim:
A signal processor, comprising: an FFT computation portion for computing spectrum data by fast-Fourier-transforming an input signal resulting from the revolving movement measured from a measuring object; a spectrum selection portion for selecting a specific spectrum corresponding to a frequency based on a number of revolutions of the measuring object: a spectrum search portion for searching sequentially the specific spectrum selected by the spectrum selection portion from the spectrum data computed by the FFT computation portion; and a search range computation portion for computing a search range of the spectrum searched by the spectrum search portion based on a frequency of the specific spectrum, the search range computation portion determining an upper limit of the search range based on a frequency less than two times a frequency of the specific spectrum, and determining a lower limit of the search range based on a frequency larger than half of the frequency of the specific spectrum, wherein, when the frequency of the specific spectrum varies, the search range computation portion computes the search range based on a varied frequency of the specific spectrum and makes the search range track the varied specific spectrum.