It’s a rather simple formula, really. Great singer + great band = Great show. Such is Karen Marguth’s “Heavy Sugar Jazz Improv” show.

Walking into Starline to see it at 5:30 p.m. on Saturday, was like walking into a time warp. Suddenly, there was no sun outside. It wasn’t Fresno anymore. No, it felt like late night at some swanky, big-city jazz club.

Marguth’s very capable band features local all-stars Rich Severson (guitar), Kevin Hill (bass) and Gary Newmark (drums), as well as featured guest pianist Jason Wanner.

And Marguth has this smooth and sultry voice that defies her look – definitely more school teacher than jazz siren (and she actually is an elementary school teacher). Her vocals, nonetheless, are downright delightful.

Not only that, but she has a good sense of pace when it came to the show. The whole thing was improv, with the musicians just taking cues from each other and letting the music go where it went. Marguth knew when to back off and let her band take over – even heading into the crowd to chat with people for a few minutes at one point. Wen it came time to sing again, she was more than ready. And so was the crowd.

At a Rogue Festival with a lot of great jazz options, this show should be near the top of your list.

Playing: 8:30 p.m. Sunday and 7 p.m. Wednesday at Starline, 831 E. Fern Ave. Cost: $7. Rating: G.