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???
11/12/06 15:56
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 		 #127820 - Re: Fundamental and harmonics.
Responding to: ???'s previous message

FFT delivers harmonics and fundamental!


Thats correct, But How does FFT algoritham know what exactly is fundamental. Albertos code which essentially seems to use Danielson-Lanczos algoritham gives an array amplitude that has 32 elements and according to the commenting in his code.
amplitude[0] = DC
amplitude[1] = Fundamental
amplitude[2] = 2N freq. and so on

But according to some other texts I found on net.
amplitude[1] = 1Hz
amplitude[2] = 2Hz and so on.

Now the confusion is which one of the above two is correct and how does the fft algorithm know the fundamental freq.

In my case the fundamental is close to 50Hz/60Hz.

Thanks & Regards,
Prahlad Purohit



List of 32 messages in thread
TopicAuthorDate
Measuring THD [ Total Harmonic distortion ]            01/01/70 00:00      
   ANalogue method.            01/01/70 00:00      
      Re: Analogue method.            01/01/70 00:00      
         fundamental flaw?            01/01/70 00:00      
            Re: Fundamental Flaw.            01/01/70 00:00      
               Digital filter            01/01/70 00:00      
                  Re: Fundamental Frequency.            01/01/70 00:00      
               FFT            01/01/70 00:00      
                  mains frequency            01/01/70 00:00      
                     Why rely on an assumption?            01/01/70 00:00      
                  Re: FFT            01/01/70 00:00      
                     FFT            01/01/70 00:00      
         What use?            01/01/70 00:00      
   Goertzel filters, maybe ?            01/01/70 00:00      
   FFT is the first choice            01/01/70 00:00      
      Is it?            01/01/70 00:00      
         If you know the fundamental.            01/01/70 00:00      
            Re: Fundamental            01/01/70 00:00      
               Multiple cycles            01/01/70 00:00      
                  The 50Hz fundamental must dominate            01/01/70 00:00      
               Fundamental and harmonics!            01/01/70 00:00      
                  Re: Fundamental and harmonics.            01/01/70 00:00      
                     You're getting into theory            01/01/70 00:00      
                     That is very simple!            01/01/70 00:00      
         I think, yes            01/01/70 00:00      
   Alfredos Code Doesnt seem to work properly.            01/01/70 00:00      
      Do you want it to write in "C"?            01/01/70 00:00      
         Yes Kai,            01/01/70 00:00      
      Eh? Endian issue.            01/01/70 00:00      
         Tags            01/01/70 00:00      
   How about this method for THD.            01/01/70 00:00      
      Mix of numerical calculation and FFT            01/01/70 00:00      

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