Desktop environment: Ubuntu 12.04 uses Unity as shell over Gnome desktop environment while Ubuntu Studio 12.04 uses Xfce as
Linux kernel: Ubuntu Studio 12.04 uses realtime kernel (for reducing the amount of latency, which is extremely beneficial for audio work) while Ubuntu 12.04 uses generic kernel(more about kernel types).
Installation: Ubuntu 12.04 has live CD for installation but Ubuntu Studio 12.04 only has live DVD.
Applications: Ubuntu Studio 12.04 contain a lot more pre-installed multimedia software (several audio, video and graphical applications) than Ubuntu 12.04.
Appearance: Ubuntu Studio 12.04 has blue-on-black theme instead of Ubuntu's default purple and orange and also a new sound theme replaces the default Ubuntu theme.
JACK Sound System : Along with the ubiquitous Pulse Audio sound server, the powerful JACK sound server is also included in Ubuntu Studio. Both are already configured to work well together.
System Configuration : There is a different configuration of the system so as to "not-limit" you audio/video processing.