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RiverFalls
USA
33 Posts |
 Posted - 05/05/2010 : 11:16:10 AM
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(Origin 8.0 SR6 and OriginPro 8.1 both on Windows XP.)
I am running an FFT on a dataset of all real values (with time values running from -10s to 10s), and then trying to use the IFFT to recover the original signal.
In Origin 8.0 SR6, there is no option to obtain a two-sided FFT (even though the online help says that there should be that option), and when I proceed with the FFT/IFFT process (being careful to Shift and UnShift in the FFT and IFFT), I do not recover the original signal. How can I recover the signal in Origin 8.0's FFT?
In OriginPro 8.1, I have the same problem, if I do a one-sided FFT, but if I do a two-sided FFT, then I can recover the original signal-except that the time values run from 0 to 20s. Is there anyway to recover the signal without doing a two-sided FFT originally?
Thank you,
Lowell
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VincentLiu
China
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Posted - 05/06/2010 : 05:46:02 AM
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Hi Lowell,
The following screenshot shows you where the Two-Sided option of the FFT tool is.
Please see whether it can help to solve the problem. If not, please sent your data and more details about the problem through
http://www.originlab.com/www/company/qform.aspx?s=1&
Best regards,
Vincent Liu
OriginLab Technical Support
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Edited by - VincentLiu on 05/06/2010 05:46:26 AM |
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RiverFalls
USA
33 Posts |
Posted - 05/06/2010 : 5:39:47 PM
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Yes, that's the option that I used in 8.1, but the 'Spectrum Type' option box does not appear in the 8.0 SR6 FFT dialog box.
So, there are two issues:
1) Not all the options ('Spectrum Type', for example) appear in 8.0 SR6
2) Is it possible to recover the original signal using only a one-sided FFT?
Lowell |
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VincentLiu
China
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Posted - 05/07/2010 : 04:18:14 AM
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To the 1st question:
I think you are using the standard version of Origin, for only the professional version of Origin has the Spectrum Type and Normalize power to option. We are so sorry that we have not made it clear in the document. We will update it soon.
To the 2nd question:
From the following link, we can find that the one-sided power density is derivate from the two-sided power density.
http://www.originlab.com/www/helponline/Origin/en/UserGuide/Algorithm_(FFT1).html
So we cannot recover the original signal using only a one-sided FFT.
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RiverFalls
USA
33 Posts |
Posted - 05/11/2010 : 1:10:04 PM
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If I recall correctly, Origin 7 used to have the 'two-sided' result as the default. Why isn't it even an option in Origin 8?
Not being able to perform an FFT and IFFT to show that the original function is recovered makes it very hard to be convinced that the FFT is working correctly. (I teach students how to use FFT's in Origin.)
I suggest that the two-sided option be returned to the regular version of Origin in the future.
Lowell |
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minimax
350 Posts |
Posted - 05/12/2010 : 01:51:24 AM
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Hi Lowell,
We have loosen the restriction and made the Spectrum Type option available in the 8.1 Regular version (current latest build is 81SR3).
See attached image, which also clearly indicates the Pro-only options on GUI.
Max
OriginLab Technical Support |
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FFT/IFFT options and confusing results