How can I implement FFT (y-axis:Power, x-axis:Frequency) with 4 cases: Lowpass/Hi​ghpass/Ban​d/Notch

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Thuan
Thuan 2014-4-1
回答： Thuan 2014-4-6
Hi,
Currently I implement FFT (y-axis:Power, x-axis:Frequency) as below: (based on http://www.mathworks.com/help/matlab/math/fast-fourier-transform-fft.html)
d1=-250
d2=250
data= d1 + (d2-d1).*rand(1,256)
Fs=30
m = length(data); % Window length
n = pow2(nextpow2(m)); % Transform length
y = fft(data,n); % DFT
f = (0:n-1)*(Fs/n); % Frequency range
power = y.*conj(y)/n; % Power of the DFT
plot(f,power)
xlabel('Frequency (Hz)')
ylabel('Power')
title('{\bf Periodogram}')
Currently, I don't know how to customize source code above for Lowpass/Highpass/Band/Notch.
Please help me, thanks for your support.
Best Regards,
Thuan Phan

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采纳的回答

Carlos
Carlos 2014-4-1
If you want to filter a signal in the frequency domain you just need to multiply your signals' frequency response (y in your code) by the frequency response of your filter.
In order to calcute your filter coefficients and if you have the filter design toolbox this tutorial has all the information you might need http://www.mathworks.com/tagteam/55876_digfilt.pdf
You can also design your filter using the fdatool or using the signal processing toolbox (here you can find all of the filter functions in the signal processing toolbox http://www.mathworks.es/es/help/signal/analog-filters.html)
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Thuan
Thuan 2014-4-1
Dear Mr. Carlos,
There are two domains to use: Digital Domain and Analog Domain. Currently, I use eeg data (in microVolt). And I will choose Digital Domain. Is this right? Thanks for your support.
Best Regards,

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更多回答（1 个）

Thuan
Thuan 2014-4-6
Dear Mr. Carlos,
I have implemented FFT with 4 filters. Thanks for your support.
Best Regards, Thuan Phan

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