Preemphasis Digital Filter , MATLAB

clc
clear all
close all
t=0:0.01:2*pi;
x=sin(2*pi*0.5*t)+0.2*sin(2*pi*4*t);
subplot(2,1,1);
plot(t,x);
title('Original Signla');
num=[1 -1];
den=[1];
h=filter(num,den,x);
subplot(2,1,2);
plot(t,h);
title('Filtered Signal');