# low-pass filter problem

From: Guangshan Chen <gchen9_at_nyahnyahspammersnyahnyah>
Date: Fri, 5 Jun 2009 11:11:52 -0500

Hi all,

I would like to use a low-pass filter on one monthly data to remove
the signal with period less than 1 year.
When I check the result, I find there still a signal in high frequency
band.

My script as follow:
print("generates the weights for low pass filter")
ihp = 0
nsigma = 1.
befaft = 17 - 1 ; number of points to use before and after
current point
nwt = 2*befaft + 1 ; total number of weights
fca = 0.06
fcb = -999.
wts_t = filwgts_lancos (nwt, ihp, fca, fcb, nsigma)
; opt=0 is chosen for wgt_runave when applying the weights to, say, a
time series
opt = 0

; low pass data
x_pass = wgt_runave_Wrap(x,wts_t,opt)
x_new = x_pass(lat|:,lon|:,time|24:tmax-24)

x_org_ts = x({lat|0},{lon|180},time|:)
printVarSummary(x_org_ts)
x_new_ts = x_new({lat|0},{lon|180},time|:)
printVarSummary(x_new_ts)

;------------------------------------------------------------------
; set parameter for spectrum
;------------------------------------------------------------------
print("calculating spectrum of eof time series....")
d = 1 ;Remove the series mean and least squares linear trend.
sm = 7
pct = 0.10

spec_org = specx_anal(x_org_ts,d,sm,pct)
splt_org = specx_ci(spec_org, 0.1, 0.95)

spec_new = specx_anal(x_new_ts,d,sm,pct)
splt_new = specx_ci(spec_new, 0.1, 0.95)

Any suggestions??

Also I have another question: how to set the precision of the Y axis?
I used these two sources:
res_spec_at_tmYLAutoPrecision = False
res_spec_at_tmYLPrecision = 4
Anything else??