> On 2004-12-08 11:06:20 +0100, Stephan M. Bernsee
<spam@dspdimension.com> said:
>
> > On 2004-12-08 10:52:35 +0100, johnbesel@web.de (Eugene) said:
> >
> >> If I have right, then I should get only one peak in FFT spectrum.
> >
> > One peak, yes, and possibly other non-zero bins (many people forget
> > about that).
>
> And actually, if your input signal is real you should get *two*
Why not try something simpler to start with ? You could input 1 2 3 4 1
2 3 4 ... repeating to fill your input ( I am assuming that it's a
power of two length > 4 ) with a nice repeating pattern - make sure
that your imaginary inputs are all zero - then when you look at the
output you should be able to check that the DC component is = sum of
the input values (if your FFT doesn't rescale internally) with no
imaginary part and that you get repeated zeros at the positions you
expect and that the peaks you see are the right values and phases. Then
you can just scale the input till it starts to fall apart due to
arithmetic errors. Once you are happy that this simple input with a
period that fits exactly into your FFT size is producing the values you
expect you can have another look at the sine input.
Best of luck - Mike
Reply by Stephan M. Bernsee●December 8, 20042004-12-08
On 2004-12-08 11:06:20 +0100, Stephan M. Bernsee <spam@dspdimension.com> said:
> On 2004-12-08 10:52:35 +0100, johnbesel@web.de (Eugene) said:
>
>> If I have right, then I should get only one peak in FFT spectrum.
>
> One peak, yes, and possibly other non-zero bins (many people forget
> about that).
And actually, if your input signal is real you should get *two* peaks, not one.
--
Stephan M. Bernsee
http://www.dspdimension.com
Reply by Stephan M. Bernsee●December 8, 20042004-12-08
On 2004-12-08 10:52:35 +0100, johnbesel@web.de (Eugene) said:
> If I have right, then I should get only one peak in FFT spectrum.
One peak, yes, and possibly other non-zero bins (many people forget
about that).
> but if I use fft function, and then show my result in "code composer
> studio" in praph/time:frequency, then I see a lot of peaks.
Not without knowing what you do exactly.
If your FFT is complex-valued and your sine wave is real, are you sure
you assign the input values correctly?
--
Stephan M. Bernsee
http://www.dspdimension.com
Reply by Eugene●December 8, 20042004-12-08
Hello,
I just started to work with DSP 320VC5416 and I try to build the FFT
of the sine signal.
If I have right, then I should get only one peak in FFT spectrum.
but if I use fft function, and then show my result in "code composer
studio" in praph/time:frequency, then I see a lot of peaks.
I think, I should do some operation with output of the fft, but wich
operation should I do?
My output is symmetrically, and I have positiv and negativ magnitude.
Can anybody help me?
thanks in advance