How to apply a bandstop filter after performing FFT

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Joydeb Saha
Joydeb Saha el 16 de Jun. de 2021
Comentada: Walter Roberson el 17 de Jun. de 2021
How to apply a bandstop filter after performing FFT on the this data, to remove the spikes ? SC is the data matrix.
rows1 =length(SC(:,2));
incr1=1/(rows1+1)*12;
fmax1=12*(1-1/(rows1+1));
X1=[0:incr1:fmax1/2]';
Y1 = abs(fft(SC(1:rows1,2),rows1));
  5 comentarios
Joydeb Saha
Joydeb Saha el 17 de Jun. de 2021
OK, I understood. But how to use the bandstop filter after the fft on this data.
Walter Roberson
Walter Roberson el 17 de Jun. de 2021
Example:
data = randn(1, 50);
plot(data)
title('original data');
Y1 = fft(data);
bins_of_interest = 5:22;
damping = exp(-(1:length(bins_of_interest)));
Y1(bins_of_interest) = Y1(bins_of_interest) .* damping;
Y1(end+2-bins_of_interest) = conj(Y1(bins_of_interest));
back_data = ifft(Y1);
whos back_data
Name Size Bytes Class Attributes back_data 1x50 400 double
plot(back_data)
title('reconstructed')
Your bins_of_interest should be chosen according to the sampling frequency and the number of points, and which frequencies you want to filter out; one of the links I posted shows how "wide" each bin is. Your "damping" could be constant or could be any curve that is appropriate for your circumstances, in recognition that you might not be wanting to filter each frequency equally.

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