gmdistribution--std before and after don't match

Hi all,

I am trying to create zero-mean, random gaussian noise to add to a signal, however, the standard deviation (std) that I specify is not the same as the std of the random points drawn from the object created by gmdistribution. I have attached my code below, can you please tell me what is wrong or give me alternatives to try?

Thanks!

sigma=0.16;
obj=gmdistribution(0,sigma);
noise=random(obj,100);
s=std(noise);

If I run the example above, I get a value of s anywhere between 0.36 and 0.45 (but I want it to be 0.16).