process using audio device

[Bram Kuijper]

Hi all,

I am using Ubuntu Gutsy. Due to some strange bug in rhythmbox, 
apparently my audio device is unreachable for any other applications 
(such as kaffeine).

Of course, I have to file a bug sooner or later on this strange 
behavior, but first I want to know how I can find out which process is 
using my audio device. Is there a command to find out what PIDs are 
using my audio device?

thanks,

Bram Kuijper