TV's Frink said:

Here's something really tedious, but provided some impressive results IIRC.

Http://originaltrilogy.com/forum/topic.cfm/Isolating-Music-and-Voices-in-Star-Wars/post/668489/#TopicPost668489

The only way you will ever get any decent results if you do everything manually by Hand.

I use Audacity because it's similar to Cubase which I started using when I was about 15 years old.

The best way to achieve any isolation with voices is to delete everything outside of the voice... That being music and sound effects wise on center channel. i.e strip it clean apart from the where the voice appears in the timeline.

Then with the vocal clips you have left with the music underlying you have to make a judgement call on equalizing out what you can from the sound. Dropping out everything outside of the vocal range is a first step.

Then the judgement call on how much you could or should slice in to what is left to remove anything else if the music / sound effects clashes in frequency.

If you have a trumpet horn say while someone is saying something it's basically game over you will never remove that and keep the voice because they are sharing the same space.

So then you need to either find an impersonator or a clean Audio sample which you probably wont get the luxury of.

To identify what you can remove boost the frequencies up. If it does not effect the vocal then you can drop it out totally.

Sometimes giving something a small dip will give you the leverage to cover it.