x = randn(100, 1);   % generate some data
db1 = 2;             % large bin width
db2 = 0.5;           % small bin width
bins1 = -4:db1:4;    % large bins
bins2 = -4:db2:4;    % small bins
[h1,b1] = hist(x, bins1);
[h2,b2] = hist(x, bins2);

bar(b1, h1)
hold on 
bar(b2, h2, 'facecolor', 'r' )
xlabel('x')
ylabel('Frequency')
hold off