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