filtering sin signal with fft

Hi all, Ihave a problam about filtering a sin signal ı must filter low frequencies(under 52 hz) and do this with fft. So ı try to do it with a fir low pass filter then fftfilt command. Did anyone suggest something else or commeny on it.

Answer 1

[Image Analyst]

What frequency is your sine signal? Why do you think there are any frequencies other than that one? Anyway, to filter, you call fft, zero out low frequencies, which will be at the low end of the array, and the high end, then inverse transform. Or you can use fftshift and zero out the middle of the fft array.

[geem]

my frequency is 50 hz which is like below fo=50; f1=52; y = 10*sin(2*pi*fo*t) + 5*sin(2*pi*f1*t); ı try to filter 52 hz interharmonic.

[Image Analyst]

OK, did you try what I said? Did you see 4 spikes in your FFT spectrum?

[geem]

if i'm wrong please correct me first i use fft then fftshift but i saw only one 2 spike

Fs=25600;

T=1/Fs;

% Length of signal

L=5120

 t = (0:L-1)*T;                % Time vector

fo=50; f1=52;

y = 10*sin(2*pi*fo*t) + 5*sin(2*pi*f1*t);

 NFFT = 2^nextpow2(L); % Next power of 2 from length of y

 Y = fft(y,NFFT)/L;

 f = Fs/2*linspace(0,1,NFFT/2+1);

% % Plot single-sided amplitude spectrum.

figure(1)

 stem(f,2*abs(Y(1:NFFT/2+1))) 

 title('Single-Sided Amplitude Spectrum of y(t)')

 xlabel('Frequency (Hz)')

 ylabel('|Y(f)|')

filt_Y2=fftshift(Y);

figure(2)

stem(f,2*abs(filt_Y2(1:NFFT/2+1)),'y');