There is a rotary control I have seen that is like the edge-on view of a knurled volume control wheel on an old Walkman.
Without knowing what it's called I can't search for it - I'm pretty sure that the app was based on Qt.
Edit - having tried it on a couple of people younger than me it seems that the iPod generation don't know volume knobs! Looks like I need to use up-down arrows instead (it's not actually a volume it's a rotate view)