[SAC-HELP] a problem while downsampling sac data with decimate

[Arthur Snoke]

Based on looking at the code, I can confirm that interpolate does not 
itself have the capability of running an anti-aliasing filter.  You would 
have to do that first yourself.

Sometimes one wants to increase the number of points.  In some 
applications I increased npts to be an exact power of 2.

If you want to compare the effects of interpolate and decimate, here is a 
suggestion.  (I have not tried it, so ...)

Take a file for which you have a RDSEED RESP file and use the evalresp 
response in transfer with FREQLIMITS set to filter the low frequencies 
but not the high.  That will give you a lot of amplitude at high 
frequencies in the saved file.

Take that file and apply interpolate and decimate separately and compare 
the outputs.