Thread: About fft routine in SAC

Started: 2008-03-08 10:59:07
Last activity: 2008-03-08 10:59:07
Topics: SAC Help
2008-03-08 10:59:07

In SAC, I generate a 5Hz sine wave and do fft transforming as follows:
sac> funcgen sine 5 npts 1024 delta 0.01
sac> fft
sac> psp am loglin
and I find that the maximum absolute amplitude is greater than 4 near
frequency 5Hz, but in theory, it should be 0.5 because of amplitude
spectrum symmetry of real series, so could you tell me why?

B.T.W., I also compute the amplitude spectrum using fft program I wrote and
find that the result is not the same with SAC generated, I checked the
program carefully and be sure that it's right and conform with the
theoretical result.

thanks for your attention!

Your sincerely,
Xu W.

Dr. WeiWei Xu
Institute of Geology and Geophysics
Chinese Academy of Sciences
P.O.Box 9825
Beijing 100029
Tel: 0086-10-62007354(Office)
Fax: 0086-10-62010846

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