Two Fretless Bass Giants Unite: Steve Di Giorgio and Jeroen Paul Thesseling on Quadvium’s “Tetradōm”

The seeds of Quadvium were planted long before a single note was recorded. For Steve Di Giorgio and Jeroen Paul Thesseling, the idea of collaborating had been circulating for well over a decade. Whenever their paths crossed on tours or festivals, the conversation would eventually come back to the same question: how could two fretless bassists merge their voices in a single project?

It wasn’t until recently that the idea became reality. The duo completed the lineup for the band Quadvium and released Tetradōm, a bold and immersive debut that draws from their collective backgrounds in classical music, metal, jazz fusion, and world traditions. The album is now available on vinyl and digitally (Apple Music, and Amazon Music), capturing a shared vision years in the making.

Fretless Bass and World Music: Influences Behind Quadvium’s Sound

“It was a big mystery how we were going to do it and what it would even sound like,” Steve said. But both bassists knew they wanted to combine the full spectrum of their experience: flamenco, death metal, Arabic scales, Moorish music, and hard fusion. Instrumental and cinematic in scope, the compositions allow each voice to move independently, yet remain interconnected.

Much of that cohesion is thanks to Eve, Quadvium’s guitarist and primary composer. Many of the compositions began as rough sketches—some rooted in world music, others in metal chaos—that Eve developed into full pieces. “Some of the songs came from older folders of ideas, and some were totally new,” Steve explained. “But once we started layering our parts, everything fell into place more naturally than we expected.”

Recording Tetradōm: Inside Quadvium’s Studio Process

Recording the album brought its own surprises. Jeroen had already worked out many of the arrangements before Steve joined him in Amsterdam, but tracking together revealed something unexpected: their tones didn’t clash. Despite using two different signature fretless basses—Jeroen’s Warwick and Steve’s Ibanez—they found their sound palettes complemented each other without stepping on one another.

“We kind of had this brief pre-notion that we’d have to plan everything carefully to stay off each other’s toes,” Steve said. “But once we started playing, it was weird how naturally it came together. We didn’t have to scoop out frequencies or adjust much—it just blended.”

Jeroen agreed, noting that the pairing benefited from each bassist’s sonic identity. “If we had used two Warwick Thumb basses or two Ibanez basses, it could have easily clashed. But the blend of instruments and styles just worked.”

Quadvium’s Bass Arrangements: How Two Fretless Players Wove Their Parts

That blend is more than tonal. It’s also structural. From unison lines to call-and-response phrasing and layered harmonies, the bass arrangements throughout Tetradōm are as carefully woven as they are expressive. And while Eve’s vision shaped much of the album’s architecture, both bassists contributed crucial ideas to the final arrangements.

“We had recorded till like 3:00 in the morning, and I was walking back to the hotel when I got a rough mix from Eve,” Steve recalled. “She was like, ‘Dude, check it out—it sounds so cool together.'”

A New Chapter for Progressive Fretless Bass

Quadvium’s debut reflects years of friendship, exploration, and experimentation. What began as a hypothetical conversation between two like-minded fretless pioneers has become something far more tangible: a new chapter in progressive bass-forward music.

And while Tetradōm stands as a singular achievement, it’s not the end of the road. Both players hope to continue the collaboration. As Jeroen put it, “I would love to start again with a fresh mind and begin working on a second album.”