>On 13 Okt, 00:22, "Peter123" <p...@[EMAIL PROTECTED]
> wrote:
>> I have implemented Jens Joergen Nielsen FFT code in my windows program
>> that converts V(t) to V(f). =A0I am using 2500 Hz sampling with
N=3D8192 =
>point
>> FFT.
>> I am plotting the FFT amplitude as sqrt(Re^2 + Im^2)/N. Im getting the
>> correct peak frequency after FFT, however, I am getting only about 1/2
of
>> the peak =A0amplitude (of the input sine wave input amplitude) with
>> rectangular window. (If my input wave is 20.0*sin(omega*t) the FFT
gives
>> ~10 for peak height at omega).
>> Using various windows (Hamming, Bartlett, etc) the V(f) peak amplitude
>> becomes even smaller.
>>
>> Any suggestion why do I get 1/2 peak heights?
>
>It's because of Euler's equations:
>
>cos(x) =3D 1/2 (exp(jx)+exp(-jx))
>sin(x) =3D 1/j2 (exp(jx)-exp(-jx))
>
>> What correction factors should I use for the spectrum height for
various
>> window types?
>
>Don't bother. You will not see the exact numbers you use
>for the amplitudes unless the frequency of the sinusoidal
>is an integer fraction of the sampling frequency,
>
>f =3D k/N
>
>wher k and N integers and k < N/2.
>
>Rune
>
Thanks Rune.
I assume 3D is the amplitude.. (why 3D?)
Peter
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