Starting tomorrow, Durham’s 9th Annual Warehouse Blues Series inaugurates four Fridays of outdoor shows at the Pavilion in Durham Central Park, with the theme of all of the shows being a focus on the slide guitar. This week’s featured performers include Jon Shain, Melissa Swingle (Trailer Bride, The Moaners) and duo the River Otters.

The performance kicks off in the park at 6 p.m. with performances in the round by the three acts. After they’ve traded tunes, the audience can join in a “Community Blues Jam” onstage with the performers. Everyone’s encouraged to bring a guitar.

How exactly all of this will work out is still a little up in the air. This is the first time the organizers are attempting this format, but it seems fun, adventurous and certainly unpredictable. The choice of a thematic focus is also a first for the series.

“We’ll be the guinea pigs and hopefully it will be good,” Shain says.

Shain laments a bit that he’s known primarily as a blues player, despite the fact he’s released several albums that have explored Piedmont country-folk and flat-picking. That said, Shain still has an abiding love of the slide guitar first gleaned from the Allman Brothers.

“It sounds a lot closer to speech. It’s easier to sustain notes on the slide and obviously, you get between the notes like people speak. We don’t speak like autotune,” chuckles Shain. Though he picked it up in high school, he really learned the instrument during the dead time working at Brian’s Guitars in Carrboro (then known as Gibson Music) in the ’90s.

“The slide is a personal thing too,” he says. “You can almost tell who you are listening to. They don’t have to say it’s Derek Trucks on the radio. You can tell it’s that sound.”

Shain points to the way the slide guitar is played as providing lots of opportunity for personal expression. When the guitarist passes the (typically) cylindrical object over the strings, there’s only a narrow contact point that’s truly in tune, mostly the guitarist slides it up and down the note creating a vibrato effect.

“You have to go equal parts sharp and flat on the note, so you’re playing out of tune to the note more than you’re playing in tune. The average is what our ears interpret as the intended note,” he says. “You can make that swing of sharp and flat, wider on both sides or you can make it narrow. The wider the swing in the vibrato, the kind of crazier it sounds. Another factor is also the speed of the vibrato.

“Contained in that is where you have so much room for people’s styles to creep in,” says Shain, with a pause. “But I don’t know if my slide paying is tell-tale yet.”

The gig this week isn’t the only thing on Shain’s calendar right now: he’s awaiting the pressings from the plant of his new disc, Reupholstered. It features a dozen covers chosen for Shain by producer Jackson Hall, who produced two other records by Shain (2007’s Army Jacket Winterand 2010’s Times Right Now). The disc also features guest appearances by members of Birds & Arrows, Lizzy Ross and Tom Maxwell, to name but a few.

“He assigned a tune for me to cover every month for a year. There’s no blues. It’s all obscure pop tunes and stuff from as far back as Cole Porter and Hank Williams on up to Elliott Smith,” he says.

As for the rest of the Warehouse Blues Series schedule, look for slide guitarist Selwyn Birchwood (July 18), Lakota John and Kin (July 25) and cigar box guitar artist Justin Johnson (August 1) through the next few weeks.