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general fft question

Jun 22, 2011 at 8:08 PM
Edited Jun 22, 2011 at 9:19 PM

FFT has about 1024 Complex Arrays as parameter.

But if i only what to draw about 20 i get a problem because i am only drawing 20 out of 1024. So i would like to calc average.

I am calculating that with a algorithm like that. I am just creating a new Complex variable. Then I am adding to the X and Y of the variable the values and divide in the end. A simple complex calculation.

But I have seen that after a number of complexes in the array of 1024 the values of those complexes (X/Y) are sooo small that i don t want to calculate them into the average. I know my english is bad so here is a screenshot:

http://s1.directupload.net/images/110622/lohcustk.png

What would you say is the average array index of the yellow line because i don t want to calc that in my programm. I want to calc so less as possible

 

EDIT:

In this screen: http://s1.directupload.net/images/110622/d7g3uw2j.png it seems like that is 1024/3 is that always something around that value or only in my livestream?

Jul 1, 2011 at 9:40 PM

You usually get the magnitude sqrt(real * real + im * im) and then take the log base 10 of it before plotting FFT.