Author Topic: FFT Speed  (Read 6250 times)

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SAMIII

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FFT Speed
« on: December 14, 2010, 06:52:24 AM »
Hello.  I'm new to this forum and was wondering if anyone could point me towards where I may be able to find data on how fast the FFT is performed in SignalScope Pro for the various sample sizes identified?  Would greatly appreciate your help.
Thanks.

FaberAST

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Re: FFT Speed
« Reply #1 on: December 14, 2010, 09:00:46 AM »
Is your question related to the actual computation time of the FFT, or are you asking about how often the spectrum display gets updated?

The actual computation time is very short (I don't know off the top of my head, and it will vary from machine to machine). However, the longer the FFT window, the more data needs to be gathered, which means it will take longer before a valid spectrum is available. For example, if you sample at 48 kHz and perform a 48,000-point FFT, you will need to gather 1 whole second worth of data (48,000 samples) before the FFT can be computed, and you'll get a new spectrum every second (with 0% overlap). If you increase the overlap to 50%, you'll get a new spectrum every half a second.

SAMIII

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Re: FFT Speed
« Reply #2 on: December 15, 2010, 06:44:14 AM »
Hi, and thanks for responding.
My question was related to computational speed.  I understand the sampling time may be the long pole in the tent, and the computational speed will vary from platform to platform....but was thinking about using the iPhone4 with remote data aquisition equipment to provide it with a faster stream of sample data and processing multiple FFTs per seconds on the streaming data set.  I don't need much time to perform other functions once the FFT is complete, but I'm concerned that the iPhone (of any variety) may not be able to keep up with, say, 10 each 4K or 8K FFTs per second.  Was hoping someone may be able to throw a ballpark number at me. 

Thanks for your great work on this product, by the way.  We're trying to buy a copy of it right now for testin and other uses.