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s2d2
Germany
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 Posted - 03/26/2007 : 10:54:18 AM
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Origin Version (Select Help-->About Origin): 6.0
Operating System: XP
Hello,
I would like to use the resulting curve of an FFT analysis in another Plot (together with other FFT curves; building sth. like an order analysis...).
The curve in the FFTPlot generated by Origin says that the FFT curve consists of Freq(X) and r(Y). But if I copy these two columns into a new worksheet, remove or hide the negative frequency part and generate a simple diagram that should show the same FFT curve as the automatically generated one, I get sth. different instead. Amplitudes in general are much lower, peaks are at different positions...
If you want, I can upload some pictures so you can see the differences.
So, what am I doing wrong? The FFT curve obviously consists of more than just Freq(X) and r(Y). Some mathmeatical funtion including the Power(Y) column? How can I copy the FFT curve data correctly?
Forgive that I am not much into the principle funtioning of an FFT. I just need the results...
Thanks for helping me out.
Oli
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Mike Buess
USA
3037 Posts |
Posted - 03/26/2007 : 12:10:01 PM
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Hi Oli,
The Amplitude curve is simply column r versus column Freq. You can convince yourself of that by selecting column r and plotting it separately. That plot must be identical to one obtained from copying columns Freq and r to a new worksheet. Perhaps you copied the Real column - which is next to Freq - rather than column r.
...Another possibility has occurred to me. Perhaps the graph of the copied data is using speed mode which limits the number of visible points to 300 by default. If your spectrum has many more points than that the apparent peak positions and amplitudes will be wrong. Speed mode is 'off' by default for FFTPlot but 'on' for most other Graph templates. Activate the graph containing the copied data, select Format > Layer, click the Size/Speed tab and uncheck the speed mode option for Worksheet data.
Mike Buess
Origin WebRing Member
Edited by - Mike Buess on 03/27/2007 4:07:00 PM |
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s2d2
Germany
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Posted - 04/02/2007 : 12:47:41 PM
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Hi Mike,
thanks for the help. Yes, the error occured due to the limitation to 300 drawn values in the speed mode.
But the problem is, that in my case (3 curves with about 1200 values each in a 3d-waterfall diagram), if I try to uncheck the speed mode option, Origin hangs up. If I try to raise the number of values to more than 800, Origin hangs up as well...
I need at least 2000 values per curve to get realistic curves. There are quite narrow but high peaks and therefore quite relevant peaks in all 3 curves...
In single curve diagrams, Origin 6.0 by default uses 3000 values. Also, I can can uncheck the speed mode.
Therefore my question: is that limitation to approx. 800 values in multiple curve diagrams a 'feature' of Origin v6 or does the same restriction exist in v7.5?
Thanks again for the help.
Oli |
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Mike Buess
USA
3037 Posts |
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Using FFT results in aanother worksheet...