clear all 
close all
pkg load signal
[y,fs] = audioread('modulator22.wav');
sound(y, fs);
n = length(y); 
t=0:1/fs:(n-1)/fs; % time range
spectrogram(y,fs,5,30);

[y, fs] = audioread('modulator22.wav');
n = 8;
Wn = 0.0453;
[b, a] = butter(n, Wn);

y = filter(b, a, y);
spectrogram(y,fs,5,30);
sound(y, fs);
audiowrite('butter.wav',y,fs);