fs = 48000;
[xn,fs] = audioread('eric.wav');
nf=1024;
Y = fft(xn,nf);
f = fs/2*linspace(0,1,nf/2+1);
plot(f,abs(Y(1:nf/2+1)));

d = designfilt('lowpassfir' , 'FilterOrder' , 8 ,'CutoffFrequency' , 4000 , 'SampleRate' , fs);
filteredf = filter (d, Y);

filteredt = ifft (filteredf);

sound(filteredf,Fs);
t = [1:1000];
Fc = 100000;
Fm = 500000;
[p,q]=rat(fs/Fm);
filtere=resample(filteredt,p,q);
filte = fft(filtere,nf);
x = cos (2*pi*Fc*t);
z = filte.*x;

demod = z.*cos(2*pi*Fc*t);
[b,a] = butter(5,Fc*2/Fm);
demod = filtfilt(b,a,demod);
z1= awgn(z , 0 ,'measured');
demod1 = z1.*cos(2*pi*Fc*t);
[b,a] = butter(5,Fc*2/Fm);
demod1 = filtfilt(b,a,demod1);
z2= awgn(z , 10 ,'measured');
demod2 = z2.*cos(2*pi*Fc*t);
[b,a] = butter(5,Fc*2/Fm);
demod2 = filtfilt(b,a,demod2);
z3 = awgn(z ,30 ,'measured')
demod3 = z3.*cos(2*pi*Fc*t);
[b,a] = butter(5,Fc*2/Fm);
demod3 = filtfilt(b,a,demod3);


z1f = fft(z1,nf);
z2f = fft(z2,nf);
z3f = fft(z3,nf);

plot(z1f);title('SNR =0 in  frequency');
plot(z2f);title('SNR =10 in  frequency');
plot(z3f);title('SNR =30 in  frequency');
plot(z1);title('SNR =0 in  time');
plot(z2);title('SNR =10 in  time');
plot(z3);title('SNR =30 in  time');
[p1,q1]=rat(Fm/fs);
z1fs=resample(z1f,p1,q1);
z2fs=resample(z2f,p1,q1);
z3fs=resample(z3f,p1,q1);
sound(z1fs,fs);
sound(z2fs,fs);
sound(z3fs,fs);

fc2 = 100100 ;
z4= awgn(z , 10 ,'measured');
demod4 = z2.*cos(2*pi*fc2*t);
[b,a] = butter(5,fc2*2/Fm);
demod4 = filtfilt(b,a,demod4);



z5= awgn(z , 10 ,'measured');
demod5 = z2.*cos(2*pi*fc*t+20);
[b,a] = butter(5,fc*2/Fm);
demod5 = filtfilt(b,a,demod5);