It’s an all-Mozart program this afternoon at Tanglewood, yet as I type these words, Mozart from Tanglewood is already pouring from my speakers, full and ripe, of an earlier vintage. Charles Munch is conducting the Boston Symphony Orchestra. It is July 11, 1958.

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About an hour ago it was the summer of 1944, and Serge Koussevitzky was leading a Tanglewood audience in a full-throated rendition of the national anthem. Next came, of all people, Danny Kaye hamming it up with the BSO in 1961.

This week, in short, I’ve been reveling in the digital streams now being released from the vaults of the BSO archives. The orchestra has been offering these streams free from its website, one per day, and will continue through the summer season. Of all the many ways the orchestra is now celebrating Tanglewood’s 75th birthday, this digital cornucopia is by far the most enticing, most revealing, and most generous. Video montages and tribute programs may gesture festively toward Tanglewood’s past, but here is the actual genealogy of a tradition: the performances themselves, as if caught and bottled just before the music disappeared into the Berkshires sky.

The streams, which date to excerpts from the very first concert on the Tanglewood grounds in 1937, are available to anyone with an Internet connection. If you like what you’ve heard, you can purchase and download it the following day, in some cases for around the cost of an iced coffee.

The Munch Mozart I mentioned comes from a performance of the composer’s beloved “Sinfonia Concertante,” here featuring the largely forgotten violin soloist Ruth Posselt and the BSO’s own famed violist Joseph de Pasquale. Listen to de Pasquale’s honeyed tone in the songful opening pages of the slow movement, and to Munch’s rich orchestral support, worlds away from the trimmer Mozart textures now in fashion.

The Koussevitzky-led “Star-Spangled Banner” precedes a forceful account of Mozart’s Symphony No. 25. With wartime gas rationing in effect, the festival of 1944 was reduced to a single group of Mozart performances. The announcer narrates the scene in period-starched voice, telling us that “Serge Koussevitzky has emerged from a summer of rest and quiet study of scores at his own estate nearby.” Yet there is nothing languid about this performance. Keeping the festival alive during wartime was, for Koussevitzky, a moral and spiritual statement, and this Mozart thunders as if to prove the point.

And happily, there is much, much more in these streams than Mozart from BSO patriarchs — the full range of more recent Tanglewood activities is also on view, from James Taylor to James Levine, the latter leading the Tanglewood Music Center Orchestra in a rapturous account of Dvorak’s Symphony No. 8. (Levine’s “Gurrelieder” of 2006 and “Les Troyens” of 2008 are due up later this summer.) There is Verdi’s “Otello” from Erich Leinsdorf, and Seiji Ozawa leading a Shed-lifting performance of Messiaen’s cosmic “Turangalila Symphony” from 1975. The composer was present and the crowd roars as he takes his bow on stage. (Messiaen, we are told, later autographed Ozawa’s score: “To the great Seiji Ozawa — his symphony.”)

On other occasions captured here, composers took an even more active role, mounting the podium to conduct the orchestra themselves. A few clicks and one can hear Copland in the Shed leading his own Clarinet Concerto, here luxuriously floated by BSO clarinetist Harold Wright. Or Luciano Berio in 1982 conducting his own landmark 20th-century work “Sinfonia.” Or John Harbison in 1984, leading a major orchestra for the very first time, in a charged reading of his own First Symphony.

Cumulatively, from assembling the audio sources, to choosing the 75, to preparing the recordings with sound engineers, this project was a vast undertaking and the BSO has done an outstanding job. The selection is only part of the story; no two listeners’ best-of list would ever be exactly the same. More important, broadly speaking, is the intelligent curating of a festival’s past.

You can download the files in MP3 or lossless (FLAC) formats, and each offering comes with both its own essay by former Globe critic Richard Dyer and excerpts from published reviews of the same performance you are hearing. How refreshing, too, that negative reviews are included along with the glowing ones, making the project feel not like marketing but like portions of an aural history.

As such it also implicitly casts a revealing light on present-day trends in Tanglewood programming. The festival has always placed the core classical and Romantic repertoire at its center, but Tanglewood clearly once also encouraged more adventures beyond that canon — not only in the safe environs of the TMC and Ozawa Hall (which did not exist before 1994), but also in the Shed, the populist heart of the festival. If Berio were alive today, could you picture him leading a mostly-Berio program in the Shed on a Sunday afternoon this August? Or Messiaen’s epic “Turangalila” performed once more for picnickers on the lawn? It seems almost inconceivable.

At least we now have these recordings, adding up to a kind of musical diary of place. And it is precisely that sense of place that makes this collection fascinating in a different way than a similar grouping of historic streams from Symphony Hall would be. Tanglewood’s geographic remoteness — the improbable concentration of high culture in the middle of the woods — lends an added dimension to these aural snapshots. You may find yourself thinking: “This happened, here?”

And for now, the streams just keep coming one a day. In the near future, keep an eye out for a Phyllis Curtin recital from 1964, a Monteux-led performance of Bartok’s Concerto for Orchestra, Jacqueline du Pré performing her signature Elgar Cello Concerto, Gunther Schuller leading his own “Spectra,” and Sir Colin Davis leading Mozart’s Requiem. Bug spray not required.