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Altera_Forum

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10-06-2011
10:43 AM

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FFT Megafunction - bit reversed or not

Hi all,

using the FFT megafunction (fixed,streaming architecture), I have been assuming the data is natural order (user guide could be clearer?) Am I wrong? My sim. output looks wrong - with simple sine input , output has two large (same amplitude) peaks per packet I have read the manual, honest! :confused:
4 Replies

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Altera_Forum

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10-06-2011
12:59 PM

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You're aware of the fact, that the frequency domain data will be mirrored around fs/2?

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Altera_Forum

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10-06-2011
02:03 PM

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Ok, thanks very much,

that would make sense.. back to school for me! thanks again,
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Altera_Forum

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10-08-2011
11:29 AM

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If your input is real sine (imag of zero) then you will get two equal mirrored peaks.

If your input is complex sine/cos (well balanced in amplitude and phase) then you get one peak only. If it is complex but unbalanced then the peaks become unequal. The real case is the extreme subset when imbalance is maximum (imag = 0)
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Altera_Forum

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10-10-2011
08:01 AM

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Kaz,

thanks so much for extra info, very helpfulFor more complete information about compiler optimizations, see our Optimization Notice.