load handel; %Load an audio signal built into MATLAB
%Array y contains the data. Fs equals the number of samples per second,
%usually 8192.
n = length(y);
plot((1:n)/Fs,y)
xlabel('Time (s)')
ylabel('Amplitude')
sound(y) %Play the audio signal
z = fft(y);
m=(n-1)/2;
z_half = z(1:m+1);
figure
plot(Fs*(0:m)/n,abs(z_half))
xlabel('Frequency (Hz)')
ylabel('Amplitude')
f_cutoff = 2500; %Hz
z_half(round(n*f_cutoff/Fs):end) = 0; %This zeros out the coefficients of terms corresponding
%to frequencies of f_cutoff Hz or more.
figure
plot(Fs*(0:m)/n,abs(z_half))
xlabel('Frequency (Hz)')
ylabel('Amplitude')
pause
z2 = [z_half; conj(z_half(end:-1:2))]; %Reconstruct the full fft
y2=ifft(z2); %ifft is the inverse fft algorithm
sound(y2) %Play the filtered audio signal