By LARRY ROHTER

For decades jazz cognoscenti have talked reverently of “the Savory Collection.” Recorded from radio broadcasts in the late 1930s by an audio engineer named William Savory, it was known to include extended live performances by some of the most honored names in jazz - but few people had ever heard even the smallest fraction of that music, adding to its mystique.

This year the National Jazz Museum in the Harlem neighborhood of New York City acquired the entire set of nearly 1,000 discs, made at the height of the swing era, and has begun digitizing recordings of inspired performances by Louis Armstrong, Benny Goodman, Duke Ellington, Billie Holiday, Count Basie, Coleman Hawkins, Lester Young and others that had been thought to be lost forever.

“Some of us were aware Savory had recorded all this stuff, and we were really waiting with bated breath to see what would be there,” said Dan Morgenstern, the Grammy-winning jazz historian and critic who is also director of the Institute of Jazz Studies at Rutgers University in New Jersey . “Even though I’ve heard only a small sampling, it’s turning out to be the treasure trove we had hoped it would be, with some truly wonderful, remarkable sessions. None of what I’ve heard has been heard before. It’s all new.”

After making the recordings, Mr. Savory, who had an eccentric, secretive streak, zealously guarded access to his collection . When he died in 2004, Eugene Desavouret, a son who lives in Illinois, salvaged the moldering discs; this year he sold the collection to the museum. Some of the boxes had been sealed since 1940. (According to his son, Mr. Savory was born William Desavouret in June 1916 aboard the ocean liner Mauretania, where his parents were passengers immigrating to the United States from France. Mr. Desavouret said he did not know why his father changed his name.)

Part of what makes the Savory collection so alluring and historically important is its unusual format. At the time Savory was recording radio broadcasts for his own pleasure, most studio performances were issued on 10-inch 78-r.p.m. shellac discs, which could capture only about three minutes of music.

But Mr. Savory, who worked at recording studios in New York and Chicago, had access to 12- or even 16-inch discs, and sometimes recorded at speeds of 33 1/3 r.p.m. That allowed Mr. Savory to record longer performances in their entirety.

Many of the broadcasts from nightclubs and ballrooms that Mr. Savory recorded contain more relaxed and freeflowing versions of hit songs originally recorded in the studio. One notable example is a stunning six-minute Coleman Hawkins performance of “Body and Soul” from 1940 . The collection contains some of the most acclaimed names in jazz playing in unusual settings or impromptu ensembles. Benny Goodman, for example, performs a duet version of the Gershwins’ “Oh, Lady Be Good!” with Teddy Wilson on harpsichord (instead of his usual piano), while Billie Holiday is heard singing her anti-lynching anthem, “Strange Fruit,” barely a month after her original recording was released.

“The record is more like a dance tempo, whereas this version is how she would have done it in clubs,” Loren Schoenberg, the director of the jazz museum, said of the Holiday recording. “You have the most inane scripted introduction ever, but then Billie comes in, and she drives a stake right through your heart.”

Because Mr. Savory liked classical music, the discs also include performances by the Norwegian soprano Kirsten Flagstad and several by Arturo Toscanini’s NBC Symphony Orchestra. There are even speeches, by Franklin D. Roosevelt and Pope Pius XII, and a broadcast of James Joyce reading his work.

The collection also provides a glimpse into the history of broadcasting, thanks to the presence of Martin Block, a radio announcer, on many discs. (The journalist Walter Winchell coined the term “disc jockey” to describe Block.) Because of deterioration, converting the surviving discs to digital form and making them playable is a challenge. Mr. Schoenberg estimates that “25 percent are in excellent shape, half are compromised but salvageable, and 25 percent are in really bad condition.”

The transfer of the collection to digital form is being done by Doug Pomeroy, a recording engineer in New York City who specializes in audio restorations . The process begins with cleaning the discs by hand and proceeding through pitch correction, noise removal, playback equalization, mixing and mastering.

M r. Savory himself played piano and saxophone, and his choice s reflect a musician’s refined tastes. “We’re lucky that he was such a jazz fanatic, because he really knew who was good and who wasn’t,” Mr. Schoenberg said.