[Seisunix] VSP Processing Bandpass filtering

Hello All I am trying to move step by step on Zero Offset VSP Processing. Now, I am trying to apply band pass filtering to my data using this: *sufilter < xcor_output_20_sources_B1.su f=5,10,15,20 amps=0,1,1,0 | filter_data.su <http://filter_data.su>* However, I did not understand how I should define the frequencies. I tried to leave the first two frequencies constant and changed the next two frequencies little by little. Then, I tried to subtract each other, using this: *sudiff file1.su <http://file1.su> file2.su <http://file2.su> > diff.su <http://diff.su>* Is there any effective way to choose these 4 frequencies in bandpass filtering? How should I learn my frequencies? If you would like to check, I added my file here. Thanks Best Regards Erdi