- ifftshift
- fft
Time-shift after fft & filter?
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Shaula Garibbo
el 12 de Jun. de 2020
Comentada: Shaula Garibbo
el 12 de Jun. de 2020
I tried to implement a simple LP filter on an audio file, but I'm slightly confused by the apparent shifting of the signal in the time domain. What have I overlooked / misunderstood? Thanks.
filename = 'Raw_Wav_20180425_000226.wav';
[y,fs] = audioread(filename);
subplot(1,2,1)
plot(t,y)
xlabel('Time (s)')
ylabel('Amplitude')
title('Raw')
fmax1 = 40; %end of pass band
fmax2 = 60; %end of transition band
nt = length(y);
t = [0:nt-1]/fs;
y = y-mean(y);
dF = fs/nt;
f = -fs/2:dF:fs/2-dF;
yft = fftshift(fft(y));
I = find(abs(f)>fmax2);
yft(I) = 0;
I = find( abs(f)>fmax1 & abs(f)<=fmax2 );
yft(I) = yft(I) .* hanning(length(I));
y = ifftshift(ifft(yft));
subplot(1,2,2)
plot(t,y)
xlabel('Time (s)')
ylabel('Amplitude')
title('Post-filter')
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Sugar Daddy
el 12 de Jun. de 2020
As you have taken fft first and then fftshift, so if you want to do inverse of this, you need inverse of fftshift first as it is performed at the end. so the order of inverse must be
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