FIR filtering & FFT processing for a signal

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MatlabGirl 2014-12-6

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评论： MatlabGirl 2014-12-7

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Hi, I have the question below:

Part 1: 1) I do not know what to design the filters to be, based on what? 2) I am not sure if I displayed the magnitude spectrum correctly. 3) how do i process the signal by the filter?

Part 2: How do I filter by using FFT processing?

please find my code is in the M-FILE attached . Your help is appreciated.

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Image Analyst 2014-12-6

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It looks like they don't care what filter you use. Why not just use a rect filter (a box)? You can do this with just convolving with ones.

firFilter = ones(1, 21)/21; % Or whatever window width you want.
out = conv(in, firFilter, 'same');

Take the FFT of both original and filtered signals and display them. Use subplot(2,2,n) to display the 4 signals all in one figure.

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MatlabGirl 2014-12-7

filter order is the number of coefficients of the filter
segmentation is something like http://dsp.stackexchange.com/questions/13370/fft-the-whole-input-vs-fft-segment they do it in case the memory is small or something

MatlabGirl 2014-12-7

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can you please check if this is correct:

% Determine the first 50 samples of this signal 
signal_first_50_samples= signal (1:50);
% Display its magnitude spectrum. 
N = 2048;
signal_spect = abs (fft(signal_first_50_samples,N));
signal_spect = fftshift(signal_spect);
F = [-N/2:N/2-1]/N;
plot (F, signal_spect) 
set(gca, 'XTick',[-0.5:0.1:1])
grid on;