6.4. Fast Fourier Transform
Time to Frequency Domains (and vice versa)
Figure 1: Fast Fourier Transform menu.
All Fourier Transforms in geopsy are based on the algorithms developed by Matteo Frigo and Steven G. Johnson (MIT) and encapsulated in FFTW library. Called the "Fastest Fourier Transform in the West", it accepts arbitrary input size for signals. On the contrary, the classical Fast Fourier Transform required the size to be a power of 2. Various papers are found in the litterature about FFTW the references of which are given at www.fftw.org.
Changing from Time Domain to Frequency Domain is not considered as a modification of the signal amplitudes, but it only alters the header information (TYPE). Hence, the transformed signals are never saved as spectra. Theoretically, successive transformations do not modify the original signal. However, due precision limits, the signal may be slightly modified. If you suspect errors of this kind, select "Revert to saved" in "Waveform" menu to get the original signal back.
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