During his shows, Michael Hedges madly twists the tuning keys on his acoustic guitar before every song. He plays almost every tune in an unorthodox tuning of his own devising and then attacks the strings with brash hammer-ons, quick pull-offs and bluesy slides and pushes. He has expanded the musical vocabulary for the acoustic guitar just when everyone thought the instrument was nearly exhausted.

"I'm trying to take the guitar in its traditional form," insists Hedges, who plays at Blues Alley tomorrow, "and tune it weird and play it weird but not have it sound too weird. It's got to sound different, though, and that's hopefully how it comes across."

The 30-year-old guitarist is one of the most popular artists on the pastoral folk-jazz label, Windham Hill; his second album, last year's "Aerial Boundaries," was on Billboard's jazz chart for 24 straight weeks. Last year he toured Europe and Japan, and this month he appears on the cover of Guitar Player magazine.

Now based in Palo Alto, Calif., Hedges grew up in Oklahoma but moved to Baltimore in 1975 to study classical guitar and composition at the Peabody Conservatory of Music. "I spent four years studying modern music at the conservatory and studying jazz guitar with Larry Woolridge on my own," he recalls, "but I earned my living at the same time playing Neil Young songs in bars by myself. That's how I developed my hybrid style."

Hedges' next album, due on Windham Hill's subsidiary, Open Air, later this year, will be his first with vocals, drawing on his songwriting since his Baltimore bar days. "I was never one to go in a straight line; I always wanted to go this way," he exclaims, spreading his arms to take in the entire room and its imaginary jars of different musical styles, "like I threw a stone in the water."