“The thing about High Zero is that, in theory, you should really, really go with an open mind,” says musician Tom Boram.

For the 25th year in a row, the High Zero Festival of Experimental Improvised Music will convene for five concerts over four days with musicians of every conceivable discipline from Baltimore, across America and abroad, arranged into unique combinations that have never existed before and may never exist again. That means, for both the performer and the audience, it’s best to rid yourself of any preconceptions of what music is or should be, and just see what unfolds on the stage at the Theater Project in midtown.

In a typical High Zero set, two to five musicians (who may not have even met beforehand) will form a temporary band and try to make a sound nobody’s ever made, listening to each other and exploring the possibilities for roughly 20 minutes. One such set on Thursday, the opening night of this year’s festival, will consist of Simone Baron on accordion, Emily Rach Beisel on woodwinds and electronics, Toshi Makihara on percussion and Chris Taylor on guitar and percussion. A series of guerilla street performances, dubbed High Jinx, will run concurrently throughout the city, so you may run into the festival even without buying a ticket.

Each High Zero program begins with a solo performance, kicked off this year by Boram, who performed at the very first festival in 1999 and is one of a dozen current members of the High Zero Collective that organizes it. When I asked him three weeks before the concert what instrument he was planning to play, though, the talkative and animated Boram was, for once, at a loss for words. “I’m not sure yet,” he said — though he’s excited about possibly bringing a harpsichord to the venue.

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The last time Boram had a solo slot, in 2009, he planned it out too much, and found himself betraying the High Zero spirit of spontaneity. “I had this amplified floor, so I was tap dancing and it went into my synthesizer. I had piano playing through electronics, and I had all these balloons on the piano that I wanted to pop, I had all these things that I wanted to do, almost like a checklist,” said Boram, who’s also a member of the long-running Baltimore experimental duo Leprechaun Catering. “And it’s like, are you really improvising? It was very contrived.”

During the 2016 High Zero Festival, Tom Boram plays a set from the bathroom that was piped onto the stage via video feed. (Stewart Mostofsky)

Boram and I met up on a recent Wednesday morning at Normal’s Books and Records, the stalwart Waverly shop where the festival was first conceived more than a quarter-century ago. A red door near the store’s checkout counter leads to the space dubbed The Red Room (though the interior was painted blue a decade ago), which became the venue for a series of experimental music performances in 1996. The first time Boram attended a show there, he met some of the founding members of the High Zero Collective: saxophonist John Berndt, percussionist Chet Pancake, and Neil Feather, who invents and builds original musical instruments.

Boram, a few years younger than the other early Red Room regulars, wasn’t initially a member of the collective, though he’s now one of its longest-tenured members. “They wanted me to be part of it, but I didn’t want the responsibility,” he said with a laugh. In the early years, High Zero was held in places like The 14Karat Cabaret, The Charles Theatre and even a Moose Lodge before the Theater Project became the festival’s permanent home. Boram cites British avant-garde guitarist Derek Bailey’s Company collective, and its annual Company Week festivals that ran from 1976 to 1994, as a significant precursor to High Zero’s format.

High Zero helped bolster Baltimore’s reputation as a hotbed of experimental music, which in turn brought new faces into the organization: The collective’s current president is Martin Schmidt of the acclaimed electronic duo Matmos, who moved here from San Francisco in 2007. The 20th festival expanded to a tour in 2018, with concerts in New York and Chicago. Partnering with the Recorded label, High Zero has released over a dozen albums of recordings from the festival.

One musician who moved to Baltimore as a direct result of High Zero is Susan Alcorn, a pedal steel guitarist who cut her teeth on conventional country and western music but also enjoys playing in situations without any structure or expectations. “There’s always surprises, when you’re improvising without a key center or a harmonic structure behind you. You have to pull things out from some kind of crazy places,” Alcorn said.

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Alcorn made her first festival appearance in 2004, and High Zero released an album of her performances, “Concentration.” “Living in Houston at the time, I was a little bit isolated. So I came up here and there’s all this music,” Alcorn remembered. “They had a crab boil on Sunday afternoon, and I was like, ‘Baltimore’s kind of a cool place.’”

Alcorn moved to Baltimore in 2007, becoming a more active member of both the Red Room scene and the broader international experimental community, performing in over 20 countries. “Alcorn makes iconoclastic, ambientish music on an instrument that’s not often heard on the stylistic fringe,” Giovanni Russonello wrote of Alcorn’s “Pedernal” in a New York Times list of the best jazz albums of 2020.

Despite eschewing established musical conventions and structures, the festival has fostered a tight-knit community of like-minded individuals. CK Barlow, an electronic musician who can sample the other performers in her High Zero sets and replay and manipulate the sounds they make, became a member of the collective in 2015 after moving here from New Mexico, where she was in another experimental music organization.

“To find this group of people that were clearly my kind of people and doing my kind of thing, it’s just been a godsend. They felt like family almost immediately. It’s been great, I can’t believe I’ve been here eight years already,” Barlow said. “I just got an email from one of my New Mexico buddies, who formed a trio with two people he met here when I brought him out to participate in the festival a few years back.”

Dancer Asimina Chremos, from Philadelphia, performs with analog tape manipulator Marta Zapparoli of Italy at a previous High Zero Festival. (Stewart Mostofsky)

For Lauren Sarah Hayes, a Scottish electronic musician currently based in Arizona who will perform at High Zero for the first time this year, the improv format allows the onstage collaborators to stimulate the others or even surprise themselves. “For me, it’s the most interesting when it allows me to do things that I’ve never done with my instrument before,” she said. “There are those processes of communication and collaboration and cooperation, or maybe the opposite, when there’s resistances and it’s not working. The audience becomes part of that.”

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Although the High Zero Collective has painstakingly curated most of the festival sets with prearranged combinations, one of their traditions is the Night of Randomization, which will be held on Friday this year. Alma Laprida, an Argentinian musician who moved to Maryland two years ago, will make her High Zero debut that night. Laprida, who plays a medieval string instrument called the trumpet marina, attended the festival last year, and has participated in a similar experimental festival in Buenos Aires. She looks forward to the challenge.

“As a spectator, it’s amazing,” she said. “The combination of musicians can be great, or it can be superbad. Knowing that this risk is there can be very thrilling. What’s going to happen? We don’t know.”

Al Shipley is a Maryland-based music and culture writer.