Ok, I have arrived at this point in trying to understand the DFT.
X(k)= x(n)[cos(2*PI*n*k/N) - j sin(2*PI*n*k/N)]
In this equation, N is the number of samples we are processing,
n is the sample index, starting at 0,
x(n) is the value of sample number n,
k is the frequency index,
j is ???? What is the value of j????
For any value of k, we get X(k), which is the content of the signal at the
frequency
kF/N, with F being the sampling frequency.
Example:
If we sample at 50Hz and take 50 samples. Each value of k would represent a
frequency of: kF/N=k*50/50=k*1=k, so, for k=1, X(k)=X(1) is the content of
the signal at 1Hz. For k=2, X(k)=X(2) is the content of the signal at 2Hz.,
and so on.
My 2 questions are:
1. Using the above equation for X(k)=X(2), with 50 samples sampled at 50Hz,
with n=2 and x(n)=9, what is the value of X(2)?
2. What is j in the equation and is it always the same, how can I determine
it, how can I use it?
Thank you.
Dan
At 03:12 PM 9/19/00 -0500, you wrote:
>"If you are not well founded in the calculus there is precious little
>available in the literature."(Quote from the book UNDERSTANDING THE FFT by
>Anders E. Zonst)
>
>I totallt agree. I bought this book because it states on the cover "A
>tutorial on the algorithm & Software for Laymen, Students, Technicians &
>Working Engineers"
>
>Well, I am a laymen and I still can't follow this book. I haven't even been
>able to understand even one complete chapter.
>
>What ever happened to the teachers? I have always believed that if a
>person really knows a subject, he can teach it. He just goes step by step,
>giving examples (in real number calculations, not greek and latin).
>
>Can anyone help me find a true tutorial, book, or guide to the FFT? I have
>looked at about 15 different Web pages on the topic and the only book I
>have seen, on the net, that might present FFT's in a way that a layman
>could learn from is priced at about $80.00. And from what I have seen and
>experienced I wouldn't bet on this book either.
>I am a good student when I set my mind on a subject.
>
>Thanks
>Dan
>
>
>
>
>
>
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>
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