# How to remove noise from a certain frequency using FFT

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Shern Wei Lee on 20 Sep 2020
Commented: Shern Wei Lee on 21 Sep 2020
I would like to know how to remove noises at a certain frequency using only the code below. Don't worry I have attached the sound file in the above so you use it. The problem I am facing is that I do not know how to do to find the index for this array to help cancel out all the noise greater than 3500 Hz or in this case the freq = 3500. I have the question of the code in here as well.
clear;
close all;
clc;
dt = 1/Fs;
N = length(y(:,1));
nu_Ny = 1/(2*dt);
nu = linspace(0, 2*nu_Ny, N);
f = Fs*(0:(N/2))/N;
F = fft(y);
figure(1);
plot(nu, abs(F))
freq = 3500;
[~, ind] = min(abs(f-freq));
F_filtered = F;
F_filtered(ind:end-ind) = zeros(length([F_filtered(ind:end-ind)]),1);
%
figure(2)
plot(nu, abs(F_filtered))
%
y_filtered = ifft(F_filtered);
%
audiowrite('filtered_sound.wav', y_filtered, Fs)

Shern Wei Lee on 21 Sep 2020
Looks like someone whispering LMAO Sindar on 21 Sep 2020
what about compared to the original signal? Does it look like it is filtering the right area? If not, my first guess would be that 'f' and 'nu' are not consistent (or at least, not what you expect)
Shern Wei Lee on 21 Sep 2020
nope it does not