One year after the Second Annual Pacific Pythagorean Music Festival’s cancellation, Del Sol Quartet returns to Old First Concerts to host an online festival highlighting the experimental innovators and traditional masters of pure-ratio harmonies. Although the Bay Area has long been a hotbed of alternate tunings, the Pacific Pythagorean Music Festival is the first local event dedicated to hearing these resonant harmonies. This year’s online format provides a unique opportunity to invite performers whose work involves large instruments that cannot easily be moved for live performance, including deVon R. Gray and Michael Harrison’s specially tuned pianos and Ellen Fullman’s Long String Instrument. Santur master Dariush Saghafi and erhu virtuoso Hong Wang will perform non-European classical tunings. Stephen Kent will work his didjeridu magic sure to expand the space inside our headphones. The festival’s featured performers also include cult vocalist Daisy Press, guitarist Giacomo Fiore, Seattle-based composer Marguerite Brown, Canadian innovator Gayle Young, and the Bay Area’s own Cornelius Cardew Choir.