The frequence in the above applet is very small (I also slow down the time step otherwise the change will be too fast for us to view it).
Normally we would not be able to hear sound at so low frequency.
It is only a simulation.
I need to find out the way to program it to make it more realistic.
May be you can try to do it with [url=http://audacity.sourceforge.net/]Audacity[/url] (which is a free audio editor).