Re: Calculating Jitter

[Fred Baker <fred () cisco com>]

you saw marshall's comment. If you're interested in a moving average, 
he's pretty close.

If I understood your question, though, you simply wanted to quantify 
the jitter in a set of samples. I should think there are two obvious 
definitions there.

A statistician would look, I should think, at the variance of the set. 
Reaching for my CRC book of standard math formulae and tables, it 
defines the variance as the square of the standard deviation of the 
set, which is to say

        sum of ((x(i) - xmean)^2)
     ------------------------
                 n - 1

where the n values x(i) are the members of the set, xmean is the mean 
of those values, and n is the number of x(i).

A sample set with a larger standard deviation or variance than another 
set has contains more jitter.

In this context, the other thought that comes to mind is the variation 
from nominal. If the speed-of-light delay between here and there is M, 
the jitter might be defined as the root-mean-square difference from M, 
which would be something like

        sum of ((x(i) - xmin)^2)
     -----------------------
              n - 1

with the same variables except that xmin is the least value in the set.