Trpguyy is right, pre-record is common and we have all been enjoying it for decades.
Can you imagine having to listen to the actual singing during the finale of A Chorus Line, ONE, with live voices all kicking and panting into their headmics for seven minutes? The heavy breathing alone would overpower the sound of anyone actually singing if those mics were turned on.
When the dancers are in the circle half of them are actually facing the upstage wall and yet it sounds completely full.
ONE always sounds as perfect as the orig cast recording each time you hear it … and there is a reason for that.
Most production numbers have a track in them these days, you can hear it kick in since it sounds too good to be true.
Pre-recorded tracks are very common in London.
Here's a clue if yu're not sure- look for radio mics eg when the guys are wearing swimwear in Mamma Mia...
Think I have told this before.
A show I was in had a certain 'sound' and we pre-recorded all the vocals with piano /bass and drums.
We[all ensemble] sang live on stage[no mics.] along with the tape=yes-reel to reel= and orchestra.
As there was a lot of dancing this was necessary.
Occasionally the tape would break-talk about 'sing out Louise then' till it was fixed.
Each song would begin---3 rim shots and you're in---true.
I would imagine any show that has Marissa Jaret Winokur in would need to have a recorded track. If they didn't, it would be too expensive to refund all of those tickets.
"When the dancers are in the circle half of them are actually facing the upstage wall and yet it sounds completely full.
ONE always sounds as perfect as the orig cast recording each time you hear it … and there is a reason for that. "
Well keep in mind as well that most ACL productions (including the original, revival and recent London revival,) have the dancers who are kicked out of the first number singing in a microphoned booth for these ensemble songs (One, some of the Montage, What I Did for Love, etc.)
Videos