dspLowPassFilter

%% spectrum
clear;
clc;
audioSpectrumLow = 20; % 20 hz
audioSpectrumHigh = 20000; % 20 khz
[input Fs] = audioread('sample.wav');
%sound(input,Fs)
N = length(input);                %% get the length of the audio signal
spectra = abs(fft(input, N));     %% do the fast fourrier transformaiton
spectra = spectra(1:N/2 + 1); %%
freqs = (Fs / N) * (0 : N/2);
stem(freqs, spectra);
figure
ylabel('amplitude');
xlabel('f(hz)')
%xlim([audioSpectrumLow audioSpectrumHigh]);
% noise frequency = 6000hz


cutoffFrequency = 3000;   %noise frequency /2
T = 1./Fs;
t = 1./(2.*pi.*cutoffFrequency); % tau
output = zeros(N,1);
for n = 2:N
    output(n) = output(n-1).*exp(-T/t) + input(n-1).*(1-exp(-T/t));
end
%sound(output,Fs);
%plot spectrum
spectra = abs(fft(input, N));     %% do the fast fourrier transformaiton
spectra = spectra(1:N/2 + 1); %%
freqs = (Fs / N) * (0 : N/2);
stem(freqs, spectra);

audiowrite('output.wav',output,Fs);