While I do love openings in shows like Phantom and Sunset Boulevard, are they really overtures? No these are NOT overtures. They are correctly termed "Preludes." The "Carousel Waltz" is also not an Overture, even thjough it is wonderful piece of music: quite possibly the greatest conceryt piece to emerge from Broadway in the 20th century.
An Overture is a short concert piece to introduce a program. For musicals it is usually a medley of proposed hit tunes. Some (GYPSY, CANDIDE) are outright classics. Others are more generic but still enjoyable if well played.
Many people here list the Overture from WEST SIDE STORY. I know teh movie had a 5 minute Overture (it can be heard on the DVD) but there was no Overture for the Broadway production which opened cold with danced Prolgue.
Early operettas often had 8-10 minute Overtures and some of these are famous: The overture from DIE FLEDRMAUS for example, or any of the Gilbert and Sullivan operetta Overtures, especially THE MIKADO.
I especially like Kern's original 1927 Overture for SHOW BOAT, Gershwin's OF THEE I SING and GIRL CRAZY overtures and Rodgers' KING AND I Overture. Also the classic Overtures from the 40s/50s: ANNIE GET YOUR GUN, FINIAN'S RAINBOW, KISS ME KATE, CALL ME MADAM, SOUTH PACIFIC, PAJAMA GAME.
Not many recent shows have used overtures. THE PRODUCERS did in try-out but it was mostly cut to segue into "Opening Night" before opening night.
Problem is modern audiences talk all the way through Overtures and don't pay attention. They don't seem to think it is part of the show.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com