The San Francisco Electronic Music Festival, founded twenty years ago, is an artist run, multi-day showcase at the Mission District’s Brava Theater Center that reliably spotlights an international cast of composers, improvisers, synthesists and sound artists. Programmed by a rotating committee of local artists, the lineup this year features headliners John Wiese, the noise figure known from Sissy Spacek and Sunn O))); Carl Stone, the minimalist and sample-based electronic music innovator; and the electro-acoustic composer Maggi Payne, a Bay Area experimental fixture through her longtime post at Mills College. (The Space Lady, psych-pop busker of the 1990s lately enjoying a resurgence, is no longer playing.) The roster balances academic or programmatic work with less cerebral yet still challenging fare, and brings together different generations of artists. A separately ticketed prequel to the festival occurs Thursday at Envelop, an immersive audio venue involving 32 speakers within the Midway (“the entire room is an instrument”), with prerecorded multi-channel works by Amy X Neuburg, Jim O’Rourke and My Cat is an Alien. —Sam Lefebvre