Earlier this month, the New York Times Magazine published an exhaustive investigation into the 2008 fire that destroyed thousands of Universal Music Group's master recordings, a trove of irreplaceable, priceless originals made over the span of nearly a century. The blaze at Universal Studios Hollywood completely ravaged "nearly all" of the masters in UMG's foremost vault, where the world's largest record company kept its "most prized" material, according to the Times.

In total, somewhere between 118,000 and 175,000 masters went up in flames. By UMG's own estimate, they contained about 500,000 individual songs from hundreds of world-renowned artists. Louis Armstrong, Ella Fitzgerald, Chuck Berry, Joni Mitchell, Al Green, Elton John, R.E.M., Tom Petty, Iggy Pop, Sonic Youth, Nirvana, Tupac—these are just a fraction of the musicians who lost massive swaths of their discographies in the disaster.

So why is that so devastating? What is a master, exactly, and what did we lose when so many of them burned?

Imagine yourself inside the room, at Apple Studios in 1969, when The Beatles recorded Let It Be. Paul McCartney is at the piano. John Lennon holds the bass. George Harrison clutches his guitar, and Ringo Starr sits behind the drums. As they play "Let It Be," as McCartney wails into the microphone, the sound goes directly onto a reel of tape; the moment goes directly onto a reel of tape. From that tape, known as a multitrack, we get the master recording. The master captures a piece of history that will never exist again, a sound that can never be recreated: It is the sole, original, physical document of the sound in that room, at that time.

Every song ever cut has a master recording, whether it's captured on tape or digitally on a hard drive. It is the purest form of that recording; there are details, textures, and sounds that you can hear on a master recording but that are imperceptible once they have been transferred off of it. Every step you take away from the master is a step away from that pure sound: You lose detail from master to LP or CD; from CD to MP3; from MP3 to Ogg Vorbis, the file type used by services like Spotify. To stream "Let It Be" into your headphones, and then to hear the master, could almost feel like listening to two different songs.

It's not just quality that makes a master so valuable. Often, during the course of a session, artists record songs—sometimes dozens of them—that never actually make it onto their albums. Often, the only place this unreleased material exists is on the master recording and the multitracks. When those burned in UMG's vault in 2008, we lost an untold number of songs that have never been heard. They are now gone forever. Of the 500,000 songs that were destroyed, there is no way to know how many were never put out, how many we never got the chance to hear, but would've cherished.

As the Times notes, our ability to record music, and the quality with which we can do it, has always outstripped our ability to play it back in full detail. That's why so many artists go back to the vault—go back to their masters—and release "remastered" albums, which, for the first time, allow us to hear records how they were intended to sound when they were made; how the artists themselves heard them, and wanted you to hear them. Often, on these remastered records, musicians will put out previously unreleased material. If any of the hundreds of artists whose music burned in the Universal fire want to do this—if they want to go back to their masters, make their songs sound exponentially better than they did when they were first issued, and treat us to songs we've never heard before—they can't. That music is gone.

This fire did not destroy just any master recordings: It destroyed tens of thousands of the world's most important albums from the world's most cherished artists on the world's biggest record labels. In some cases, as the Times notes, entire catalogs from labels that UMG absorbed, like Chess, Decca, and Interscope, were annihilated. That's to say nothing of the hundreds of masters from obscure, virtually unheard-of artists—artists who made incredible music yet to be discovered by labels like Soundway or the Numero Group, who specialize in dredging up phenomenal, forgotten acts from the past—that are now gone forever.

What we know we lost in the Universal fire is devastating. Even more so, perhaps, is what we don't know we lost: the music we never heard, the artists we never discovered, the songs that never got released, and never will.

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