Sorry, I should have clarified further... 'lip sync' and 'mime' are not the same thing. 'Mime' is a different type of performance altogether!

A 'lip sync' performance is usually performed 'live' by the chorus members to lend some ambience, even though it is also on the pre-rec.

We used to do this with the 'Childrens Pageant' at the Royal National Eisteddfod of Wales because of the difficulties of miking up a large number of children who were often on stage for a very short time. The children did perform 'live', but lip sync was used to ensure the audience could hear! I don't know about the current practice, because we haven't been involved with it for a number of years.

The tapes were recorded like 'radiogram stereo' - the accompaniment on one track and the vocals on the other, so it could be properly balanced in the live mix.