SACRAMENTO, Calif. - This week the center of the universe for all things harmonica is in Sacramento.

More than 400 harmonica players from around the nation and the globe will descend on the city starting today for the 46th annual convention of the Society for the Preservation and Advancement of the Harmonica, or SPAH.

Some of the biggest names in the harmonica world will partake, like legendary blues player Charlie Musselwhite, Hollywood session player Tommy Morgan, and Nashville legend Jelly Roll Johnson. And this year the festival has invited one of the world's best classical harmonica players: Jia-Yi He.

"Audiences will have the opportunity to see the best players in the world this year," said Tom Stryker, president of organization. "And the best thing about this convention is that you can sit down and rub shoulders with them."

The performance roster reads like a who's who of the harmonica, as does the list of harmonica manufacturers that will have a presence, including M. Hohner, Seydel, Suzuki, and a group of boutique manufacturers.

One of the most noteworthy things about this convention is its intimate scale. Although more than 400 players will attend, the organization likes to make the convention an approachable experience for beginner and professional alike. And the focus, musically, is an ecumenical one, including blues, jazz, classical and world harmonica.

Unlike other instruments, the harmonica has always had a populist image, given its portable size and its low cost. And it can be easily thought of as the show-up-and-play jamming instrument.

The jam sessions are one of the most appealing aspects of the convention. For Nashville-based country harp player Jelly Roll Johnson, it's a big reason to fly across country to attend. Johnson has been blowing into the harmonica for the last 37 years; he can be heard on an impressive number of country recordings, from Kenny Rogers discs to those of Trisha Yearwood.

Johnson won't perform at this year's festival. Instead, he will lead a seminar on the harmonica. And he is looking forward to taking part in the jam sessions.

Those sessions begin late, usually after 11 p.m. Johnson is drawn to them because of their democratic nature.

"The jams are very cool. You'll have maybe two or three guitar players and sometimes an upright bass player next to a snare drum in a circle of harmonica players that could be 35 harmonica players in all," he said.

The players that participate come from all skill levels.

"Some of the best players can be sitting next to a player who has only been playing a year or two. Everyone gets a turn," Johnson said. "And sometimes it's the guys you've never heard of that impress you the most."

The roster this year includes players who transcend our notions of what can be done with the harmonica, such as Bruce Kurnow, who accompanies himself on stringed harp while playing diatonic harmonica bolstered by a neck rack. And then there is Jia-Yi He, the harmonica wizard who performs classical music while holding four or more harmonicas.

"Jia-Yi is a flawless player," said Stryker.

The Chinese-born He will make his convention debut when he performs the four-movement Yellow River Harmonica Concerto and other works.

"This is an extremely difficult piece, and Jia-Yi will use 18 different harmonicas from the tremolo to the chromatic harmonica."

The importance of Jia-Yi He at the convention cannot be underestimated as he represents the largest market for the harmonica: China.

"The harmonica is very popular in China," said He, who lives in Queens, N.Y. "There are millions of young and old harmonica players there."

Some of the largest harmonica events in the world are held in China, including the Asian Pacific Harmonica Festival, which was held last year in Hangzhou, China. That festival drew 1,500 competitors.