Improving on Mozart?

Everyone who saw “Amadeus” remembers Mozart desperately trying to finish the Requiem in D minor before he died. But he lost the race with time, and the work was completed--not by rival composer Antonio Salieri, as depicted in Peter Shaffer’s 1979 play--but by Mozart’s pupil Franz Xaver Sussmayr.

Sussmayr, most scholars agree, botched things up, although his edition has become the standard one.

Many people since then have rushed to Mozart’s aid.

The latest is Harvard pianist and professor Robert Levin, whose performing edition of the Requiem will be sung by the Pacific Chorale led by John Alexander on Sunday at the Orange County Performing Arts Center in Costa Mesa.

“I’ve always been a staunch advocate of the Sussmayr edition,” Alexander said in a recent phone interview from his home in Laguna Beach.

“Last time I did it, I made a big statement that 20th century reconstructions were not necessarily going to be any better than an 18th century composer’s, especially one who was a student of Mozart.

“But I have changed my tune. And it’s this particular reconstruction that has changed my tune.”

For the ordinary listener, spelling out the differences among any of the editions can be numbing, especially when recounted in detail. Many are minute. But several changes in Levin’s edition are major and noticeable.

“The ‘Osanna’s’ of the Requiem that we all know and love are all weak movements,” Alexander said. “They’re short. They’re awkward.

“Sussmayr doesn’t lead them through the normal process a fugue goes through. He does an exposition and then quickly ends it. Even to a novice listener, it sounds strange.”

Levin has rewritten and considerably extended these sections.

“It’s really extraordinary what he’s done with them,” Alexander said. “In this instance, I think Levin did a better job than Mozart’s pupil did.”

The Harvard professor has also regrouped some of the material and purged the instrumentation.

“Sussmayr used a heavy orchestration that Mozart never used,” said Alexander. “There’s a tremendous amount of doubling in the winds. The trombones double the choir continually. Mozart never used them that way, only at structural points.

“Levin has taken all the doublings out. He’s gone back to Mozart’s principals of orchestration and created a texture that is so much clearer and more beautiful.”

Alexander discovered Levin’s 1991 version thanks to one of his conducting students who was working on a comparative study of the editions. This is his first time conducting it.

“He came up with the thesis that this was the best one,” he said. “I was skeptical at first. Then I looked at it. Then I decided it was.”

The Pacific Chorale, according to the conductor, basically has to learn only three new fugues and several new parts of other sections.

“Levin left most of the choral writing alone,” Alexander said. “Most of it will sound like home territory. Then in three movements, you’re someplace else.

“This just puts a new light and freshness to it that I think is valuable. It’s not just playing with something that should not be done.”

Haydn’s “Lord Nelson” Mass, named in honor of Admiral Horatio Nelson’s defeat of Napoleon at the Battle of the Nile in 1798, will complete the program.

As it turns out, Alexander will conduct this work, too, in a new edition that omits the traditional wind parts.

“The wind parts didn’t have anything to do with Haydn,” Alexander said. “They were put in by his publisher after Haydn’s death because he didn’t think it would be performed the way Haydn had written it--for trumpets, timpani and strings. So, this also creates a kind of brand new work of Haydn.”

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* John Alexander will conduct the Robert Levin edition of Mozart’s Requiem on Sunday at 7 p.m. at the Orange County Performing Arts Center, 600 Town Center Drive, Costa Mesa. The program also will include Haydn’s “Lord Nelson” Mass. $14-$48. (714) 662-2345.

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Chris Pasles can be reached at (714) 966-5602 or by e-mail at chris.pasles@latimes.com.