Sitting at the Yamaha grand piano in his Brooklyn apartment, surrounded by two laptops, an iPad, a monitor, a video camera and studio lights, Dan Tepfer plays the first of Bach's "Goldberg" Variations. The piano is a Disklavier, which can record and play back. When he finishes, Tepfer taps a button on his iPad, triggering the piano to play back what he's just recorded with the notes inverted, as if the score were turned upside down.

Tepfer says the project, called "#BachUpsideDown," was a result of his live performances grinding to a halt last year. "As soon as the pandemic hit, I asked myself, what can I do?" he says. "What can I do that's going to be meaningful musically right now, when the bottom has dropped out? And the first thing that came to mind was this #BachUpsideDown project, because it was something I knew I could do from home easily."

It helped that the 39-year-old musician could also write code to program his piano to invert the familiar Bach work. "When you describe what he's doing, it sounds like a gimmick," says New York Times chief music critic Anthony Tommasini. "But then when I actually heard them, I thought, oh no no no: it's beyond gimmick. It's really interesting. Ultimately, I think the point of the upside down stuff is to make us hear better, or in a new way, Bach's 'Goldberg' Variations."

The next project Tepfer tackled during the pandemic was a series of jazz concerts with other musicians in their apartments miles away, streamed live over the internet. But to make that happen, he had to find a way to overcome the lag between the signals.

"Necessity is the mother of invention," he says. "I discovered this software, JackTrip, that's actually about 10 years old, this pretty obscure academic piece of software that's brilliantly written. And it ferries musical information over the internet as quickly as possible—much, much more quickly than something like Zoom, for example."

Tepfer began to host weekly concerts, more than 50 in all, with noted musicians, including saxophonist Melissa Aldana, percussionist Antonio Sanchez and bassist Christian McBride. Last summer he streamed a program of French songs with vocalist Cécile McLorin Salvant, who says she admires Tepfer for the breadth of his knowledge. She describes his talents as vast—beginning with his mastery of livestream technology.

"He teaches people who are completely technologically inept like me how to set it up and make it work—that's one thing," Salvant says. "But then to bring it in with his beautiful piano playing, his incredible taste, his sensitivity as a musician, and then he writes his music... it's just so exciting to see somebody that bold with how they blend their interests."

Dan Tepfer was raised with blended interests. He was born in Paris in 1982 to American parents: his mother sang at the Paris Opera, and his father was a biologist. He started classical piano lessons when he was six, but spent his summers in Oregon with his grandfather, who was a jazz pianist. He started writing programs for his father's Macintosh Plus when he was nine.

At the University of Edinburgh, Tepfer majored in astrophysics. "This is what always fascinated me, is the structure underlying the surface of what we see," he says. "And physics shows you that you can explain an amazing amount of that in the language of mathematics."

That way of seeing the world, he says, has directly influenced his work: #BachUpsideDown is about extracting the music's DNA, then improvising on it. His background in math is at the heart of another project he calls Natural Machines, a project that involves an algorithm he wrote that allows his piano to accompany him while he improvises.

Tepfer says his next project is a virtual reality app that will allow users to experience Natural Machines inside 3-D visualizations of the music. But the more he branches out with algorithms and Bach experiments, he says, the more he feels the need to deepen his roots by playing with jazz musicians. Tepfer studied jazz composition in graduate school at the New England Conservatory. When he moved to New York, he played and recorded with the late saxophone legend Lee Konitz to launch his career.

Now, between 60 and 300 fans from around the world log in for each of his current livestream concerts, during which and he reads and responds to their comments in real time between the musical numbers. Tepfer says that's the thing he's most proud of achieving during the pandemic: "engaging in a real dialogue with my audience and creating a sense of community.

"At the end of the day, I think the most important thing about music is that it brings us together," he adds. "That's its role. And especially when we're so isolated, we need that more than ever."