discrete fourier transform
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hi everyone,
i want to analyze the signal with disturbance using DFT and suppress those disturbance. so pls give me an idea to suppress the disturbance.
thank you in advance.
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Wayne King
2011-10-27
Hi, probably the easiest thing to do is to look at the data's spectrum and identify which frequency content you want to retain. Then, design a filter to attenuate those frequency regions you do not want to retain.
You can use spectrum.periodogram to look at the spectrum. Then, you can use fdesign.lowpass, fdesign.bandpass, fdesign.highpass to design a filter for your data.
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Wayne King
2011-10-31
Fs=1000;
t=0:1/Fs:.3;
x=cos(2*pi*t*200)+randn(size(t));
Hs=spectrum.periodogram; % Use default values
plot(psd(Hs,x,'Fs',Fs))
Then visually inspect the spectrum to see where you would like to pass and where you would like to attenuate. Also note how many dB you would like to attenuate.
thangam
2011-11-1
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Wayne King
2011-11-1
you have to provide more detail if somebody is going to help you.
Did you read the reference material for fdesign?
Wayne King
2011-11-5
Hi, because the filter has been designed as a lowpass filter. When you filter a signal, you multiply its Fourier transform by the Fourier transform of the filter impulse response.
You have designed a lowpass filter, so its action on any input signal is to lowpass filter it and since much of what we call "noise" is higher-frequency oscillations, you get an output with less noise.
However, people often design filters with specific specifications and goals in mind, so it can very well be that a filter that works well in one scenario, must be redesigned to work in another.
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