When using subtitle('MY TITLE','PorpertyName','PropertyValue'...), or subtitle('MY TITLE') after a group of subplots, then it provides a title MY TITLE with any property used that is defined in the original title function in Matlab, but without affecting the titles, xlables and ylabels of any of the subplots.
Make sure to use the function after the group of subplots.
Example
x = 0:0.01:6;
subplot(221), plot(x,sin(x)), xlabel('x'), ylabel('sin(x)'), title('sin(x)')
subplot(222), plot(x,cos(x)), xlabel('x'), ylabel('cos(x)'), title('cos(x)')
subplot(223), plot(x,sin(2*x)), xlabel('x'), ylabel('sin(2x)'), title('sin(2x)')
subplot(224), plot(x,cos(2*x)), xlabel('x'), ylabel('cos(2x)'), title('cos(2x)')
subtitle('Single title on top','FontSize',12,'Color','r')
See also:
title, suplabel, subplot