Still, the producers preferred to spare Wood's feelings, complimenting her frequently at playback sessions. (In Nixon's sparkling, hard-to-put-down 2006 book "I Could Have Sung All Night," Nixon recounts how studio musicians were a lot less diplomatic during Wood's recording sessions.)
The goal appeared to be to keep the actress from walking off the set. If so, it worked. When filming was completed, Wood moved on to another studio to start work on "Gypsy," a musical that better suited her voice — she did her own singing in that one. Meanwhile, cleanup for "West Side Story" began.
"With Natalie, the powers-that-be didn't pay attention to the fact that she was not quite in sync with her own track all the time," Nixon said. "Her own lip-syncing was off. She was not with the orchestra."
Nixon had to re-record several tracks that could, after considerable editing, be made to fit with what Wood's lips were doing onscreen, a painstaking process. It earned Nixon increased respect.
"Saul Chaplin [the film's associate producer] told me, 'We hired you not for your voice, but for your iron nerves,' " Nixon said.
The singer's chameleon ability to produce the right voice as needed was not put to the test just in the case of Wood.
Nixon also ended up dubbing some of Rita Moreno's singing in the picture. The actress was out sick when the "Quintet" number was recorded, so Nixon did double-duty dubbing — she's the voice of Wood and Moreno in that piece.
She also made a crucial, nonsinging contribution to "West Side Story." As Nixon tells it, the cast was a little punchy by the time they shot the final scene — the death of Maria's beloved Tony (played by Richard Beymer). The scene called for a distraught Wood to run to the body.
"She falls on him and says, 'You keeeled heeem.' All the actors would find something silly about that," Nixon said, "and would start giggling instead of weeping. Natalie would start laughing, too. They finally got one take they could use, but you could tell that Natalie was still trying to stifle her laughing. So they had me dub her lines in later — without the giggle."
Nixon had an easier time when she was hired to do the singing for another celebrated actress, Audrey Hepburn, in another hugely popular movie musical, "My Fair Lady."
"Audrey was very astute," Nixon said. "She could listen to her own track and know full well it was not quite right."
In the end, Nixon sang almost all of the score in that 1964 film. And by that time, her work as "ghost" singer was more publicly recognized (though still not with a film credit) and better compensated. For "West Side Story" and all the above-and-beyond that went with it, the studio refused Nixon's request for royalties.
"In the end, Lenny Bernstein gave up one-quarter of a percent of his own royalties," the singer said. "That was spectacular."
Nixon, who received the George Peabody Medal for Outstanding Contributions to Music in America from the Peabody Institute in 2011, has always been more than a dubber.
Her long career includes acclaimed performances of opera ("I loved Mozart") and musical theater, including stage productions of "The King and I" and "My Fair Lady" that gave her a chance to sing and act the lead roles.
She also tackled thorny works by the likes of Arnold Schoenberg and Pierre Boulez with great success, toured with Liberace ("A great showman, a good piano player … very funny") and Victor Borge.
Nixon doesn't seem to mind that her ghost work in films invariably gets so much attention to this day, and she has not tired of "West Side Story."
"It's just a brilliant musical, and they made it into such a good movie," she said. "I think it holds up very well. In the end, the play's the thing. You don't want to be aware of the dubbing."
If you go
"West Side Story," with live accompaniment by the Baltimore Symphony Orchestra conducted by Marin Alsop, will be presented at 8 p.m. Thursday at the Music Center at Strathmore, 5301 Tuckerman Lane, Bethesda; 8 p.m. Friday and Saturday, 3 p.m. June 16 at Meyerhoff Symphony Hall, 1212 Cathedral St. Tickets are $33 to $95. Call 410-783-8000 or go to bsomusic.org
A roundtable discussion with Marni Nixon and three actors from the 1961 film "West Side Story" will be held at 7 p.m Friday at Meyerhoff Hall.