j = square root of negative one ( sqrt(-1) ) Remember the DFT returns complex numbers. --- [EMAIL PROTECTED] wrote: > 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 > > > > > > > > > > > > > >_________________________________________________________________________ > >Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm > >Mersenne Prime FAQ -- > http://www.exu.ilstu.edu/mersenne/faq-mers.txt > > > > > > > > _________________________________________________________________________ > Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm > Mersenne Prime FAQ -- http://www.exu.ilstu.edu/mersenne/faq-mers.txt __________________________________________________ Do You Yahoo!? Yahoo! Photos - 35mm Quality Prints, Now Get 15 Free! http://photos.yahoo.com/ _________________________________________________________________________ Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm Mersenne Prime FAQ -- http://www.exu.ilstu.edu/mersenne/faq-mers.txt
