FFT, an abbreviation for Fast Fourier Transform, is an algorithm to transform time series signal to frequency axis signal. A continuous signal voltage from sensors such as vibration detector or microphone is sampled in regular intervals, and performed analog-digital conversion to FFT calculation. To avoid aliasing phenomenon that provides us with the frequency components which do not exist in actuality, low pass filter is used before sampling. FFT processed signal is calculated to power spectrum, frequency response or others and made best use of presuming abnormal part of the instrument or natural vibration measurement of structures which is difficult in waveform analysis. For more details, see the page [Ono Sokki Technical Report (FFT Analyzer)].