THE magic of Tanglewood, the summer festival in western Massachusetts, has many parts. There is the music of course, this being the summer home of the Boston Symphony Orchestra. There is the beauty of the surroundings, both on the meticulously maintained campus in the quaint town of Lenox and all around in the Berkshire Hills.


There is a spirit that has evolved over three-quarters of a century, stemming from the festival’s founder, Serge Koussevitzky, the music director of the Boston Symphony from 1924 to 1949; nurtured under music directors like Charles Munch and Erich Leinsdorf, and influential guests like Leonard Bernstein and Lukas Foss; and now combining the youthful energy of students at the Tanglewood Music Center with a unity of purpose across generations. That spirit splintered briefly some 15 years ago, when Seiji Ozawa, the orchestra’s music director at the time, crossed swords with longtime faculty members, but it seemed to come back stronger than ever under James Levine, the music director from 2004 to 2011.


There is even a tinge of pride — a slight sense of indomitability, perhaps — shared by performers and audiences alike, born of their having repeatedly weathered terrifying flash storms and survived the annual plague of mosquitoes. Mud is part of the creation myth, as witnessed in the photograph of well dressed patrons tiptoeing over the newly soaked grounds at a Wagner concert in 1937 — in the festival’s first season, before the concert shed was built — often printed in the Tanglewood program.


Alas, this disparate yet potent mix of elements cannot be bottled. But happily the music can be, to some extent, and has been, in the form of archival recordings now being made available in quantity.


The Boston Symphony begins its two-month series of concerts at Tanglewood on Friday, with Christoph von Dohnányi conducting Beethoven’s Fifth and Sixth Symphonies and “Leonore” Overture No. 3. You should not assume that the storm movement in the Sixth (“Pastoral”) will be merely figurative. Then, on July 14, the orchestra celebrates its 75th anniversary in Lenox with a gala concert featuring a number of Tanglewood regulars, including the conductors John Williams and Keith Lockhart, the cellist Yo-Yo Ma, the pianists Emanuel Ax and Peter Serkin and the house balladeer James Taylor.


To broaden the celebration the Boston Symphony is also releasing daily downloads from its archives over 75 days, reliving its past in all its variety. The downloads, digitized and remastered, are streamed free for a 24-hour period, starting at 8 each morning, and available thereafter for purchase on the festival’s Web site, tanglewood.org.


They began on June 20 with a concert performance of Verdi’s opera “Otello” by the Boston Symphony from 1969, starring Richard Cassilly, Sherrill Milnes and Maralin Niska, and conducted by Leinsdorf. They continue on Sunday with a 2009 performance by Mr. Taylor, the Boston Pops and the Tanglewood Festival Chorus, conducted by Mr. Williams. And they end on Sept. 2, with Mr. Ozawa’s first Tanglewood appearance and last performance there as music director: Bizet’s Symphony in C with the Boston Symphony, from 1964, and Randall Thompson’s “Alleluia” with the Tanglewood Music Center fellows, from 2002. (The Thompson work was commissioned by Koussevitzky in 1940 for the opening exercises of what was then called the Berkshire Music Center.)


The Boston Symphony’s season, meanwhile, ends on Aug. 26 with — as always of late — Beethoven’s Ninth Symphony, conducted this year by the veteran Rafael Frühbeck de Burgos. Like mud, the Ninth was intimately tied to the festival’s creation, a point driven home by a couple of the downloads.


The earliest item in the collection is not a musical performance at all but an intermission lecture by Olin Downes, then a critic for The New York Times, for radio broadcast. Its main subject is Beethoven’s Ninth, for a performance conducted by Koussevitzky on Aug. 5, 1937, and it is delivered in an academic style not much in favor these days, but it imparts genuine insights about the work and its place in music history.


“Now he was seeking a new path,” Mr. Downes says of the Beethoven of the Ninth as distinct from the composer of the eight earlier symphonies. “Now he was talking of infinity. Now he himself was gazing into chaos, seeking his own path, creating a new form, of which he himself could not see the full extent and limitations.”


(Many of the downloads include radio commentary: as here, often fascinating in itself. It is often delivered in the distinctive dulcet tones of William Pierce, the radio voice of the Boston Symphony from 1954 to 1991. With a slight lilt in his delivery, he managed to sound authoritative without seeming authoritarian, though again, his manner now sounds a bit stilted and dated.)


The 1937 Beethoven Ninth does not appear here, since only two to three minutes survive on acetate discs, but the one from the next season, on Aug. 8, 1938, also conducted by Koussevitzky, does. It does not make for easy listening. You hear rotation and surface noise from the acetate discs on which it was recorded, and the shift from one disc to the next often produces a radical change in the quality and character of the sound. And you have to think that a badly tuned landing in the lower strings at the end of the introduction to the finale stems from issues of recording, not performance. (Koussevitzky was, after all, a double-bassist.) Late in the finale of my CD transfer, there is a fade-out and a skip of many measures, said to be repaired for download.