Re: Filters

[kessler@xxxxxxxxxxxxx (Billy Kessler)]

Easy. Low-pass and subtract: Original - Low-pass = High-pass

I like the low-pass filter @spz, which is a triangle. Any of the
filters except the boxcar will do the job, though. The boxcar can
have "ringing" that may contaminate your time series. Try the
following experiment to see the ringing:

yes? let zigzag=sin(x*3.14159)
yes? plot/line/sym=27/x=0:10 zigzag,zigzag[i=@sbx:3]

Ringing means that you get energy at opposite phase (or negative
frequency).

An alternate, where you can see that @spz does not produce ringing,
just smoothing:

yes? let zigzag=sin(x*3.14159/2)
yes? plot/line/sym=27/x=0:10 zigzag,zigzag[i=@sbx:5],zigzag[i=@spz:5]

Billy K