Re: Discrete Fourier Transform

*To*: mathgroup at smc.vnet.net*Subject*: [mg43863] Re: Discrete Fourier Transform*From*: Mariusz Jankowski<mjankowski at usm.maine.edu>*Date*: Thu, 9 Oct 2003 01:54:38 -0400 (EDT)*Organization*: University of Maine System testbed server*References*: <bm0juq$prl$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Catherine, Fourier[x] gives you N=Length[x] Fourier coefficients. The resoution is 1/N Hz or 2 Pi/N radians per second (assuming, of course, that the samples of the time series x are spaced 1 second apart). To change the resolution pad the sequence with zeros: Fourier[PadRight[x, M]] For more details consult any modern undergraduate EE textbook on signals and systems, such as Oppenheim, or Haykin, or Carlson. Mariusz >>Hello everyone, >> >>I am attempting to perform a discrete Fourier transform on a time series >>using Mathematica 4.0. (I'd like to determine the period of the signal.) >>Unfortunately, I noticed that I cannot control the frequency resolution of >>this transform. I also have no idea what units the frequency is in. >> >>Do you know of any way to get around the problem? >> >>Thanks so much. >> >>Catherine Neish