There is an applet to show sound spectrum and play sound effect: [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1073.0]EJS version of Fourier Synthesis (You can hear the sound,too!)[/url]

You might want to check out [url=http://audacity.sourceforge.net/]audacity[/url] if you want to record and show sound spectrum.