lab4 - Spring 2009 EE 341 Lab 4: The FFT and Digital...

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Spring 2009 EE 341 Lab 4: The FFT and Digital Filtering Due: In your discussion section June 2-5 When using a digital computer, frequency analysis means using a Fast Fourier Transform (FFT). This necessitates we spend some time becoming familiar with using the FFT to study the frequency content of a discrete-time signal. 1. MATLAB function FFT In this problem you will learn how to use the MATLAB command fft . First, use the help feature in MATLAB to learn the syntax of the fft function. The FFT function computes the Discrete Fourier Transform (DFT) of a sequence. In general the FFT of a sequence will be a complex function so you will need to look at the magnitude and phase separately. The MATLAB commands abs and angle are useful for obtaining the magnitude and phase of a complex valued sequence. Also, since the FFT only has values at discrete frequencies, it may be useful to do the plots with stem to reinforce that idea, but continuous frequency plots (i.e. using plot ) are often used since they are closer to the DTFT that you are ultimately interested in. The FFT outputs a sequence that corresponds to the range π 2 0 Ω , where is the discrete frequency (or Ω 1 0 f for normalized discrete frequency f ; 2 / Ω = f ). You are probably more familiar with seeing the spectrum plotted over the range Ω (or 5 . 0 5 . 0 f ). The fftshift function can be used for this purpose.
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lab4 - Spring 2009 EE 341 Lab 4: The FFT and Digital...

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