[pstricks] beats in postscript

[aratyn at uic.edu]

The project is to graph oscillations :
y (x) = A sin (omega+omega_0)t/2  sin (omega-omega_0)t/2
which are called beats for small values of omega-omega_0.
Is there a way of improving the ugly figure I got below
or is it an intrinsic problem of postscript
not being able to handle quick changes in direction.
Thanks, Henrik
-----------------pstricks file follows-------------------
\documentclass[12pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{pst-plot}
\thispagestyle{empty}
\begin{document}
\begin{center}
\begin{pspicture}(-0,-2)(12,2)
\psset{xunit=1.2mm,yunit=.5mm}
\psaxes[Dx=10,Dy=10,linewidth=1.2pt]{<->}(0,0)(-1,-65)(120.5,65)
\psplot[plotstyle=curve,%
	linewidth=.3pt,%
	linecolor=black]{0}{120}
	{95 x mul 180 mul 3.1415 div sin  
	.8 x mul 180 mul 3.1415 div sin mul 
	50 mul}	
\end{pspicture}
\end{center}
\end{document}
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