fs = 8000; 
t = [1:fs*0.5]/fs;
f = [220, 330, 263];
x = [cos(2*pi*f(1)*t), cos(2*pi*f(2)*t), cos(2*pi*f(3)*t)];
f1 = f*2;
x1 = [cos(2*pi*f1(1)*t), cos(2*pi*f1(2)*t), cos(2*pi*f1(3)*t)];
f2 = f1*2;
x2 = [cos(2*pi*f2(1)*t), cos(2*pi*f2(2)*t), cos(2*pi*f2(3)*t)];
sound([x, x1, x2], fs)


