extracting required information from the received wave

I'm trying to perform demodulation of the received wave at the receiver end. The problem is that after receiving the wave i want to extract my required data from that wave. Could someone please help me with that. I'm sharing the code i've written here. I can't figure out how to cut short my x axis so as to get all my required data and eliminate any unrequired data.

%MATLAB CODE FOR DESIGNING THE RECEIVER

A=5;
f1=150;   
fc=500;
fs=8000;
a=audiorecorder;
disp('start')
recordblocking(a,5);
disp('stopped');
y=getaudiodata(a);
% audiowrite('p.wav',y,8000);
% [p,fs]=audioread('p.wav');
                                            
% Assign figure number to original recording
N = length(a);                                          % These lines set the x axis of the original plot to time in seconds
                                           
dt = 1/fs;                                              % "
t = dt*(0:N-1); 

figure(1)
plot(y);                                             % Plot the recorded audio
title('Original Recording');                            % Add title to original audio plot
sound(y);   
dd=cos(2*pi*f1*t);              
fd=dd.*y;                           %multiplying with high frequency carrier now
figure(2)
plot(t,fd)
                   
        
%filtering starts here
wn=fc/fs;
[s,t]=fir1(50,wn,'low');
figure(3)
freqz(s,t) 
 x=filter(s,t,y);
 figure(2)
 plot(t,x),title('filter')
figure(3)
 plot(t,result);