Thread: About fft routine in SAC

Started: 2008-03-08 10:59:07
Last activity: 2008-03-08 10:59:07
Topics: SAC Help
wwxu
2008-03-08 10:59:07
Hi ALL,

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
China
Tel: 0086-10-62007354(Office)
Fax: 0086-10-62010846
************************************************


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