This is what Silverman has to say in _The Acoustic Mirror_ (46):
 
"[A]lthough Reynold's voice is in fact used for most of the songs, it is
replaced by that of Betty Noyes for the number "Would you," which is sung
in _The Dancing Cavalier_.  Thus, whereas Lina seems to sing the song in
the film-within-the-film, and Kathy [Reynolds] within the diegesis proper,
a third third voice, outside both fictions, actually generates the melody.
Most baroque of all, in the scenes where Kathy is depicted as postdubbing
Lina's dialogue for her, what we in fact hear is the normal speaking voice
of Jean Hagen, the actress playing Lina--a voice which contrasts
dramatically with the one Hagen employs whenever Lina speaks _in propria
persona_."
 
Silverman's footnote sends us to Rudy Behlmer, _America's Favorite Movies:
Behind the Scenes_ (1982), 267-68.
 
Cheers!
 
--Jim Buhler
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