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jvs:fscan:manual:chapter2:expression:bandpass

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jvs:fscan:manual:chapter2:expression:bandpass [2011/09/18 22:29]
voyvodic 		jvs:fscan:manual:chapter2:expression:bandpass [2023/02/23 18:43] (current)
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  **usage:  -expr bandpass flag slowfreq fastfreq scalefact**\\  **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.+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). 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. SCALEFACT is a scaling factor; FFT output intensity values will be divided by SCALEFACT. Default SCALEFACT is 1000.
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   * 1 - frequencies are in Hertz (default: frequencies are seconds)   * 1 - frequencies are in Hertz (default: frequencies are seconds)
   * 2 - 2-d spatial filtering [not implemented yet] (default is temporal filtering)    * 2 - 2-d spatial filtering [not implemented yet] (default is temporal filtering) 
-  * 4 - make output wordsize same as input (default: output is FLOAT32) +  * 4 - frequencies are number of cycles across time course (default: seconds or Hertz) 
-  * 8 - filter out 0 frequency (default: 0 freq mean signal is preserved) +  * 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:\\ Example:\\
-   %%    -%%expr bandpass 0 30 3            ; filter out frequencies below 30s (0.033 Hz) and above 3s (0.33 Hz) +<code> 
-   %%    -%%expr bandpass 1 0.033 0.33      ; same as above +   -expr bandpass 0 30 3            ; filter out frequencies below 30s (0.033 Hz) and above 3s (0.33 Hz)  
-   %%    -%%expr bandpass 0 10 40           ; filter out frequencies between 10s (0.1 Hz) and 40s (0.025 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) 
 +</code>
  
 **See Also:**\\ **See Also:**\\
jvs/fscan/manual/chapter2/expression/bandpass.1316384996.txt.gz · Last modified: 2014/08/04 16:03 (external edit)

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