Brain Imaging & Analysis Center

usage: -expr bandpass flag slowfreq fastfreq scalefact

The BANDPASS function will filter out both low and high frequency signals. 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).

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.
FLAG:

• 1 - frequencies are in Hertz (default: frequencies are seconds)
• 2 - 2-d spatial filtering [not implemented yet] (default is temporal filtering)
• 4 - make output wordsize same as input (default: output is FLOAT32)
• 8 - filter out 0 frequency (default: 0 freq mean signal is preserved)

Example:

   -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
   -expr bandpass 0 10 40           ; filter out frequencies between 10s (0.1 Hz) and 40s (0.025 Hz)

See Also:
fScan Home, fScan Manual, CmdLineOptions, Expression Command, Manual Help