For slack-key guitarist Ledward Ka'apana, ki ho'alu evokes "a Hawaiian feeling ... always."

"It's the feeling of relaxation," said Kaua'i strummer Paul Togioka.

For Dwight Kanae, it's an opportunity "to meet up with other slack-key artists to share ideas and share tunings and technique."

Ki ho'alu is calming — "nice and melodic with a relaxing style with rhythm, a beat and a melody you get with just one guitar," said Albert Kaai.

These musicians are part of an all-star cast of strummers performing at Sunday's Hawaiian Slack Key Guitar Festival, the go-to event that assembles the cream of the crop and newbies of the genre.

For Milton Lau, a guitarist who also is the chief mover and shaker of the annual event, "slack key has become synonymous with Hawai'i."

And there's an emerging market elsewhere.

"I'm just amazed with the progress of slack-key and the popularity over the years," said Lau, whose Kahoku Productions is presenting the festival here as well as similar gatherings Sept. 3 on the Big Island and Nov. 19 on Kaua'i.

Ka'apana has toured the Mainland extensively and usually exhibits his slack-key tunings along with his vocals, so his groundbreaking work has been one of the uncharted factors in the renewed popularity of ki ho'alu.

Of course, with two CDs taking the Hawaiian Grammy Award the past two years — the first was Charles Michael Brotman's compilation, this year's was another assembly by Daniel Ho — the floodgates have been flung wide open.

"When I was at the Grammys last February, I met several (Mainland) musicians," said Lau. "And because I was wearing a name tag that said Hawai'i, the first thing these guys said was 'slack key,' and they associate Hawai'i with ki ho'alu, and vice versa. It's almost like wearing a brand."

Ka'apana and Togioka both have new CDs timed to the slack-key festival, released on Lau's Rhythm & Roots label. Kanae and Kaai are among 15 ki ho'alu musicians featured in a third new R&R release, "Hawaiian Slack Key Kings," due after the weekend event.

Ka'apana's disc, "Grandmaster Slack Key Guitar," mixes vocals with instrumentals, much like his live performances. "I love playing guitar, but if a song matches my voice and fits my range, I'll sing," he said.

Togioka, 46, is a full-time engineer and finds escape and release through his music. "It's good therapy; I feel real fortunate and lucky in this life to have this serious hobby. I don't have a regular gig anymore, but I do about 15 to 20 special functions a month."

Togioka's new CD, "Here, There and Everywhere Slack Key Guitar," includes a salute to Israel Kamakawiwo'ole, linking "Over the Rainbow" with "White Sandy Beach." "It's a tribute to Iz because at a lot of my bookings for weddings, the song is highly requested," he said. "I arranged it in a slack-key tuning. I don't know how to explain it, but when I do something like this, the right tuning makes it work; very often, what I do is tape it as I'm arranging, so I don't forget."

Kanae is a full-time musician with regular gigs. On Tuesdays and Wednesdays, he performs at the Mai Tai Bar of The Royal Hawaiian hotel; on Thursdays, Fridays and Saturdays, he's part of Kawika Trask and Friends, playing poolside at the Renaissance Ilikai Waikiki; on Sunday nights, he's at the Hula Grill at the Outrigger Waikiki Hotel.

His original composition, "The Lokelani Lullaby," will be part of Lau's compilation disc, though the title tune may change. Now 50, Kanae said he learned his slack tunings from his mom when he was 17. "I've been playing slack key since," he said.

Kaai, also performing on the new compilation, said the joy is in the listening. "To me, when somebody hears slack key, along with the squeak, heads turn," he said. "When I play for friends, surrounding hotel rooms, the visitors all come out; it's hard to describe. I remember what Raymond Kane told me: 'When you play slack key, you play it sweet.' Martin Pahinui also told me that."

Kaai offers a medley of "Ke Honi" and "Lihu'e" on the album. By day, he's a driver with The Bus, on the No. 4 route (University and Nu'uanu). He has been playing slack key for 35 years, learning in a backyard jam with then-neighbor Iaukea Bright and now plays Fridays with a trio called the Ko'olau Serenaders at Honey's at the Ko'olau Golf Club in Kane'ohe.

Ka'apana is thrilled "to get the younger generation to consider this music," he said. "They always say, 'Uncle, I like learn to play slack key,' and they come to classes and I help them out with the basics. Haole from the Mainland — the younger ones — are really interested and take our workshops at the Outrigger. I guess it's because the music's sweet and smooth. When I travel, I always bring my guitar and play at the airport while waiting for flights; immediately, you see the people put their books away and they start listening, then clapping. Makes us feel good."

Reach Wayne Harada at wharada@honoluluadvertiser.com.