Different Sound-Peaks from the Sound-Card-Input (Line-In) or from a CD-Rom

Hi there!
Does anyone know how I can get the different Sound-Peaks from the
Sound-Card-Input (Line-In) or from a CD-Rom? I want to do some kind of
VU-Meter.
At this time i've got a VU-Meter, I only need something were I can get the
Data for it now.

Thanks,
   Lars

PS: Is there a package to handle  the Data?