[pstricks] adding noise to a signal

[jmpapy]

Dear pstricks users,

does anybody knows how to generate a realization of a normally 
distributed random variable b(n) and to add it to an existing 
discrete-time signal s(n) drawn using pstricks ?

For instance s(n) can be drawn as follows:
\documentclass[a4paper,10pt]{article}
\usepackage{pst-all}
\usepackage{pstricks,pstricks-add}
\begin{document}
\begin{pspicture}(-5,-0.2)(5,5)
\psline{-}(-5,0)(5,0)
\psplot[linecolor=red,plotpoints=50,showpoints=true,linestyle=none]%
{-1}{3}{4.7 39.48 x 1 neg add 2 exp mul 1 2 exp add div}
\end{pspicture}
\end{document} 

I would want to display s(n)+b(n) with b(n) white and Gaussian noise.

thank you in advance

JM

Ps: I got some strange error messages when sending this e-mail, so I 
apologize if you recieve multiple copies of this message