Low pass filtering
- To: mathgroup at smc.vnet.net
- Subject: [mg41665] Low pass filtering
- From: Bob.Buchanan at millersville.edu (Bob Buchanan)
- Date: Fri, 30 May 2003 03:56:14 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hello, I have a question about recovering a filtered signal from a Fourier transformed input signal. I have read a time series of real sampled values into Mathematica. I can use Fourier[] to compute its DFT. As I understand the DFT, the kth value represents the "amount" of the kth frequency present in the original time series. To implement a simple low pass filter I set all the elements of the Fourier series below a certain threshold frequency to zero. Now I want to do the IDFT to recover a filtered time series containing only the low passed frequencies. However the IDFT I compute is not a real series, but contains complex entries with nontrivial imaginary parts. What about this filtering operation am I misunderstanding? Thanks, Bob Buchanan