With Lou Reed’s wavering tenor and jangling guitar ringing in my ears, I stared down at the cassette tape in my hand. Was it possible I had really discovered an unknown Reed album? I was at the Andy Warhol Museum in Pittsburgh, in July 2017, doing research for a book about Warhol’s relationships with, and influence on, musicians in the 1970s — and listening to any tape I could find that had something about music on it. The collection contains thousands of tapes, and I’d heard all kinds of things on them, from Warhol’s gossipy dinner conversations about rock stars to bootleg recordings of Led Zeppelin and Elton John concerts. Warhol taped everything.

But this tape was different, and it wasn’t labeled, as most were, in Warhol’s handwriting. The initials “A.W.” were scrawled on the first side, and “Philosophy Songs (from A to B and Back)” on the second.

“A.W.” presumably stood for Andy Warhol, but on Side 1 I heard a mix of several live performances by Reed. Warhol hadn’t recorded them, though. As I would later figure out, Reed had selected and dubbed songs from different soundboard recordings from his 1975 tour to create an ideal set list for Warhol. As an example of a personalized mix tape, this was a stunning find in and of itself.

But the second side! It held 12 full songs that I had never heard before. I’ve taught courses on rock and punk for more than 20 years at Cornell University, so I know Reed’s catalogue well, from his influential 1960s band the Velvet Underground to his beautiful tribute to Warhol, “Songs for Drella” (1990), and beyond.

Unlike the mix of prerecorded songs on the first side, the songs on this second side of the cassette sounded like a demo made, most likely, in Reed’s apartment. He sang softly and close to the microphone, accompanying himself on an acoustic guitar with simple rhythmic strums. I couldn’t hear anyone else on the tape; only the sounds of traffic and Reed shuffling paper disturbed the quiet between songs.

Most of the lyrics in these “Philosophy Songs” are based on catchphrases and stories drawn from Warhol’s book “The Philosophy of Andy Warhol (From A to B and Back Again),” published in 1975. Reed runs though such topics as being a success, “business art” (a term Warhol used to describe his art in the 1970s), drag queens and fame. At times he turns Warhol’s pithy remarks into fodder for critical barbs: Warhol writes, “People used to say that I tried to ‘put on’ the media,” and Reed sings, “I’m a put-on.” Musically, a few of the songs resemble others Reed was working on at the time, such as the boogie groove of “I Wanna Be Black” and the hard-rocking “Leave Me Alone” (both of which would appear on “Street Hassle,” in 1978).

These songs were never professionally released, so it was entirely possible that no one else had ever heard them before, except maybe Warhol. And no one but me was going to hear them anytime soon: The Warhol Foundation forbids all notetaking, transcribing, quoting or audio reproduction of the tapes. Since I couldn’t copy the songs or transcribe the lyrics or music, for two days I listened to the tape over and over, desperately memorizing details of the dozen songs — lyric phrases, tempo and key, guitar chords and rhythm.

Driving home from Pittsburgh to Ithaca, N.Y., I was agitated — both exhilarated and bewildered. What was the story behind this tape? When, exactly, was it made and why? Where could I go to find out? As it happens, I was heading directly to my next important find: a treasure trove of firsthand Reed knowledge in my own backyard.

After that six-hour drive, I needed to unwind, so I headed to a local bar, a favorite haunt. As I blathered on to several of my bar buddies about my big discovery, beer in hand, one of them broke in: “I know Lou Reed’s bass player. He lives close by. Want me to give him a call?”

That was how I came to know Bruce Yaw, a member of the jazz fusion group the Everyman Band, which got its start as Reed’s backing band from 1975 to 1978. Yaw was part of the “back to the land” generation and eventually escaped the grind of city life for rural tranquility in Upstate New York. (Doug Yule, Reed’s Velvet Underground bandmate, once lived in the area too.)

Yaw, who died in September, at 73, shared with me his personal archive of tour documents, soundboard recordings and demo tapes and, as important, his memories of touring with Reed. Using his archive, I was able to piece together the live performances that Reed included on the “A.W.” mix tape and hear echoes of a few “Philosophy Songs” in the demos for the 1976 album “Coney Island Baby” (including early versions of “I Wanna Be Black” and “Leave Me Alone.”)

My research eventually led me to more digging in the recently opened Lou Reed Archive at the New York Public Library. There I made another discovery: a second partial copy of “Philosophy Songs” on a tape that also contained the Eagles’ album “One of These Nights,” recorded from the vinyl. (Who knew Reed was an Eagles fan?) On this tape Reed is listening to his acoustic demo of “Philosophy Songs” and messing with the audio playback, even running it through a distortion box to make a roaring blast of noise.

Lou Reed: untitled excerpt from "Warhol Philosophy Songs." From the Lou Reed Archive, New York Public Library for the Performing Arts. (Courtesy of the Lou Reed Estate)

By reading documents in the collection and listening to Warhol’s taped dinner conversations with Reed, I gradually unearthed the story behind the cassette: In early 1974, Warhol approached Reed to create a Broadway musical based on Reed’s “Berlin” recording of 1973, a bleak concept album about a couple’s struggles with addiction, domestic violence and death. It would have been their first major collaboration since working together with the Velvet Underground, for whom Warhol served as mentor and manager in its early years. After the “Berlin” musical fizzled, Reed went on tour with his new songs for “Coney Island Baby,” and Warhol went on to write the “Philosophy” book, giving a copy of the prepublication proofs to Reed. Did they ever revive their plans for a new joint project? The “Philosophy Songs” suggest they had. But once again the discussions came to nothing. Reed recorded the tape in the late months of 1975, after his tour ended — and probably after the hopes for a musical collaboration ended, too. As performed, the “Philosophy Songs” sound more like a bitter parody than the basis for a creative partnership.

The tape functions as an audio double portrait: One side is Reed, the other is Warhol, whom Reed does not portray in a particularly good light. The lyrics hint at Warhol’s aura of vacuity and his callousness toward the deaths of regulars at the Factory — Warhol’s studio — such as Candy Darling and Eric Emerson. It is also a musical document of their decade-long friendship, filled in equal measure with admiration and disappointment.

Discovering such an artifact in an archive is a music historian’s dream. Discovering Bruce Yaw through my network of Ithaca friends was dumb luck and an immense pleasure. Altogether, as Lou Reed sang on his “New York” album, stumbling on this remarkable musical document was the “beginning of a great adventure.”