fScan Reference Manual, Chapter 2 (CmdLineOptions:Expr): Bandpass
usage: -expr bandpass flag slowfreq fastfreq scalefact
The BANDPASS function will filter out both low and high frequency signals from a time series data set. Usually, frequencies slower than SLOWFREQ and faster than FASTFREQ will be filtered out.
For convenience, frequencies are typically expressed as wavelengths in seconds, so a slow frequency cut-off would be something like 30-60s and a high frequency something like 2-3s, depending on what frequency wavelengths you want to preserve. If SLOWFREQ is faster than FASTFREQ, then BANDPASS acts as a notch filter to remove frequencies between SLOWFREQ and FASTFREQ (instead of frequencies outside that range).
Note: For temporal filtering, the data set time dimension should have the correct data sampling units (e.g. TR interval) specified; if the time unit is 0 (or negative) a 1s sampling interval is assumed.
SCALEFACT is a scaling factor; FFT output intensity values will be divided by SCALEFACT. Default SCALEFACT is 1000.
The FLAG argument can be used to select filtering options.
-expr bandpass 0 30 3 ; filter out frequencies below 30s (0.033 Hz) and above 3s (0.33 Hz) -expr bandpass 1 0.033 0.33 ; same as above, specified in Hertz -expr bandpass 4 10 100 ; filter out frequencies below 10 cycles and above 100 cycles -expr bandpass 0 10 40 ; filter out frequencies between 10s (0.1 Hz) and 40s (0.025 Hz)