jvs:fscan:manual:chapter2:expression:bandpass

**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.

FLAG:

- 1 - frequencies are in Hertz (default: frequencies are seconds)
- 2 - 2-d spatial filtering [not implemented yet] (default is temporal filtering)
- 4 - frequencies are number of cycles across time course (default: seconds or Hertz)
- 8 - make output wordsize same as input (default: output is FLOAT32)
- 16 - filter out 0 frequency (default: 0 freq mean signal is preserved)
- 32 - no filtering (test FFT → reverse FFT)

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, 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)

**See Also:**

fScan Home,

fScan Manual,

CmdLineOptions,

Expression Command,

Manual Help

jvs/fscan/manual/chapter2/expression/bandpass.txt · Last modified: 2014/08/04 16:03 (external edit)