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Old 31st August 2013, 12:11 AM   #11
SY is offline SY  United States
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Nope, you're right on base.
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Old 31st August 2013, 02:12 AM   #12
JMB is offline JMB  United States
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Thanks. Then to take it one step further, I assume one would use the same windows that you have used for FR for CSD and for Tone burst and for the same reasons?
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Old 31st August 2013, 02:46 AM   #13
Jay is offline Jay  Indonesia
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. Would anyone be kind enough to explain this in light of frequency response, THD and IMD measurements, burst measurements, and CSD? John K had advised to just stick with Blackmann Harris for SE while the ARTA manual suggests different windows for different circumstances. thnx.
I don't know why you ask this because it is clear that each windowing has compromises so you will want to compromise frequency accuracy or transient accuracy depends on the information you want to seek and the nature of the input signal.

If you know too much about the subject of course it is good to use the most appropriate windowing for each cases. But let me tell you that the interpretation of measurement regardless of accuracy is still a weakest link. So you will need long time to be able to well interpret the result of any windowing. In your situation it is best to stick with one type. A type that is in the middle compromise for general purpose measurement is probably the BH4. I choose Hann because most important masurements require the frequency domain accuracy.


Windowing option is also related with FFT size and processing speed. For final measurement the accuracy should be better than trials.
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Old 31st August 2013, 03:06 AM   #14
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FFT size and processing speed.
No longer relevant in most cases.
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Old 31st August 2013, 03:25 AM   #15
Jay is offline Jay  Indonesia
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Originally Posted by scott wurcer View Post
No longer relevant in most cases.
I don't know what you mean with no longer relevant but I think it was me who is not clear about what I was saying. My main point was about choosing different "accuracy" for trial and final. Because the more accurate the measurement the more processing is required hence time. I'm not talking about BH7 for final and no windowing for trials, no, but in general term including choosing the sample size.
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Old 31st August 2013, 03:28 AM   #16
jcx is online now jcx  United States
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if you are using the same clock, say a soundcard or DAQ, for both source, record then you can skip windowing altogether if you make any frequency input an exact integer fit

asynchronus frequency interference like power line noise will splatter though

Last edited by jcx; 31st August 2013 at 03:34 AM.
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Old 31st August 2013, 03:31 AM   #17
Jay is offline Jay  Indonesia
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Btw, my computer was top when I bought it, now I realized that I'm way behind. Actually I work with computers but that feeling when I bought my computer blinded me that my computer is only 2GHz and 2G RAM when the last time I checked.

Indeed software development is left way behind hardware development. And I don't play games so Photoshop is the critical software for me then
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Old 31st August 2013, 12:20 PM   #18
JMB is offline JMB  United States
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Thanks all, for helping me to better understand this. Sy, between your explanation and feyz over at the PE forum

FFT and Windowing

along with the links:

Windowing: Optimizing FFTs Using Window Functions - National Instruments
The Fundamentals of FFT-Based Signal Analysis and Measurement in LabVIEW and LabWindows/CVI - National Instruments
Characteristics of Different Smoothing Windows - LabVIEW 8.2 Help

, I feel like I have a much better ability to apply this.

Jay
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Old 31st August 2013, 12:33 PM   #19
SY is offline SY  United States
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Wow, he's a more prolific typer than I am!

The value of a tool is proportional to the user's understanding of it. You're taking the right approach.
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Old 1st September 2013, 10:31 PM   #20
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Originally Posted by Jay View Post
I don't know what you mean with no longer relevant but I think it was me who is not clear about what I was saying. My main point was about choosing different "accuracy" for trial and final. Because the more accurate the measurement the more processing is required hence time. I'm not talking about BH7 for final and no windowing for trials, no, but in general term including choosing the sample size.
My bad, I misunderstood your comment.
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