Two creative forces in Philadelphia are teaming up to put on a show during the Fringe Festival. The popular rock band Dr. Dog and the award-winning experimental performance group Pig Iron Theatre are staging a performance that defies categorization.

Knowing the facts about this production will not help you understand it. So we will start with the fiction:

Fifteen years ago, members of Dr. Dog received in the mail an unsolicited cassette tape from someone named Phrases. It's a collection of lo-fi songs and homemade advertisements bathed in audio muck. It was created by Phrases in a primordial place called the Psychedelic Swamp.

"There's this guy named Phrases. He lived a very humdrum life. A 9-to-5, wake-up, go-to-bed lifestyle. He wanted to get away from it. He was fed up. He was done," said Toby Leaman, bassist and singer with the band. "He found a way to get into the swamp. He loved it at first. Then he realized he's doing the same thing, but now he's got dragonflies, cattle frogs, dry rot, and weird psychedelic stuff, but it's still the same. Nothing has changed."

The band accepted the songs as a message, a warning, and a challenge: the Psychedelic Swamp is a fun and fascinating place, but not one that will change your life.

"If you're trying to escape something, you're just going to repeat it in a strange abstract way," said Leaman.

None of this is true.

Dr. Dog made the Psychedelic Swamp tape itself, when the band first formed in 2001 as an offshoot of a previous ensemble called Raccoon. "Psychedelic Swamp" was self-produced and self-released. It was not the album that broke Dr. Dog.

Now, 15 years later, the band is going back into the swamp, re-interpreting its own origin story to make more accessible pop music out of that earlier dirge. Dr. Dog is recording tracks for an upcoming release, expected later this fall.

Enter Pig Iron Theatre. The experimental theater company and the pop-rock band have shared members in the past. They had been talking informally about doing something together for a long time.

"We talked about all kinds of different things," said Dan Rothenberg, co-founder of Pig Iron. "Then Dr. Dog said, 'There is a cassette tape, and a story of Phrases, a tape sent in the mail, and we have a mission to bring the music to the world. But that's not something Pig Iron would want to do.'"

Rothenberg knows a weird story when he hears it. "We said, 'No! Tell us more!'"

For "Swamp is On," a show performing at the concert venue Union Transfer, Dr. Dog plays the subject of an elaborate scientific experiment, involving a radio antenna picking up signals from the Psychedelic Swamp and a giant machine that consumes magnetic tape and spits out wavelengths of light and imagery. A team of scientists and security agents prowl the stage as the experiment devolves.

Audience members will be invited to bring cassette tapes to submit them to the onstage machine designed by Matt Saunders.

"Not submitting, as much as sacrificing," Leaman corrected. "These things are being shucked like an oyster. Tape is fuel. There's only one way to run this thing, and it's magnetic tape."

Following the hour-long theater piece will be an actual concert by the band, no frills.