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FFT length doesn't correspond to output? DSP builder

Altera_Forum
Honored Contributor II
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I'd really appreciate some help, I've been working at this for some time now, 

 

I'm trying to verify my fft megafuntion in dspbuilder. I'm using a 64 point length streaming architecture, for the input just a sine wave source block. I've been plotting the results in matlab and what confuses me is the output frequency components don't repeat within my transform length. I would expect the output to be a stream of data each sample between my source sop and source eop, but in stead I See the data begin to repeat after maybe several or more sop - eop cycles. Can anyone tell me why? I know the output is dependent on the sampling frequency,is this my simulation clock? Thanks :D
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Altera_Forum
Honored Contributor II
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One possibility is that your sine input is played broken in phase per 64 frame. Try set your sine input to 16 or 32 or 64 data points per cycle.

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Altera_Forum
Honored Contributor II
227 Views

Thanks Kaz, 

 

that was my problem. This seems to restrict the frequencies I can transform. Is this a reason to use a different architecture/higher precision?
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