ATHENS - As a child in West Georgia, Hugh McGraw didn't appreciate the unique tradition of the music his parents sang. He ran and played while older relatives lifted their voices in songs from 100-year-old hymnals passed down from generation to generation. As a young man, that same sacred music took hold of him, and he had to learn to sing in that style.

"The first time I heard it in 1953, it just sent chills all over my body," said McGraw, now 79.

On Sunday, a few dozen people, including McGraw, gathered in the visitor's center at the State Botanical Garden of Georgia to sing those old songs in the traditional way, a singing style called Sacred Harp.

Performed a cappella, Sacred Harp uses shapes to denote pitch in musical notes; "fa" is a triangle, "sol" an oval, "la" a rectangle and "mi" a diamond. More than 150 years ago, the shapes helped music teachers who traveled to rural areas quickly to teach children to read music, so that an entire town could follow a hymnal in only a couple of weeks.

The vocal parts in Sacred Harp music are written with equal importance - no dominant alto or supportive bass - and since everyone sings at full volume, only a few voices fill the room.

"The music does not follow conventional rules," said John Garst, a retired professor who edited the modern reprinting of "The Social Harp," a Sacred Harp hymnal originally published in 1855 by a Hart County man named John G. McCurry.

"Each part is a good, singable melody, and you don't have discords," Garst said. "Otherwise, we pay no attention to what modern theorists would call harmony."

While the style started in New England, it flourished and survived in the South.

Today, pockets of people in rural areas still sing Sacred Harp, but more people travel to annual gatherings such as the one in Athens this weekend to share the tradition.

The Sacred Harp Musical Heritage Association publishes minutes from meetings conducted across the country each year, listing the page number and leader of every song the choir performed that day. Most of the meetings are in Georgia, Alabama and Mississippi, but the minutes record meetings in California, Oregon, even the United Kingdom.

Many Sacred Harp adherents have sung in the style their whole lives.

Others are reaching back to a part of their heritage that fell out of practice in their grandparents' generation.

"Most of the singers who come are not reconstructors," Garst said. "They are people whose parents and grandparents sang Sacred Harp. They came up in it.

"But those people are mixed in with people who came to it recently."

Michael and Jane Spencer didn't know about Sacred Harp singing before they moved to South Georgia a decade ago, he said, even though her mother was a professional Appalachian storyteller.

But when they arrived in Hoboken, they discovered a group that sang in the traditional way.

"They were isolated. They didn't know anyone in the world was singing that style," Michael Spencer said.

Today, the Spencers live in Bishop and are active with the local Sacred Harp group, which has staged the annual gathering for 37 years.

Some of the traditions of Sacred Harp may be lost to history. The back cover of the reprinted "The Social Harp" contains a disclaimer that some of the information may be incorrect since only a handful of the original copies survived and none had an intact cover. (Since that printing, one copy has been found.)

Still, more people are learning about the tradition. A 2007 PBS documentary, "Awake My Soul," told the history of Sacred Harp singing and how it survived in the South.

McGraw, who now lives in Bremen, did his part to spread the tradition.

He still gets tiny royalty checks for his appearance in the 1980 movie "The Long Riders," starring the Carradine brothers and Dennis Quaid, among others.

He was hired to sing in a funeral scene of the movie about outlaws Frank and Jesse James.

The producers knew nothing about Sacred Harp except that it would have been sung in the James' time, so they allowed McGraw to pick his hymn.

He chose No. 34, "To the Land."