Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
14 years ago

FFT length doesn't correspond to output? DSP builder

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

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    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.

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    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?