Over the years, the World Saxophone Quartet has played with different instrumentations, adding a rhythm section, an African drum ensemble or a guitar. But it's those four saxophones that have always defined the group's sound, and that's what will be on display when the group performs on the North Side Saturday night.

When the quartet organized in the mid-1970s, the original members were Oliver Lake, Hamiet Bluiett, David Murray and Julius Hemphill. Murray and the late Hemphill will be replaced by saxophonists Greg Osby and James Carter, two performers and band leaders.

"Osby and James are two of the best players on the scene," said Lake from his home in New Jersey. "They are really strong players."

Lake, who is making his third appearance in Pittsburgh as part of the City of Asylum Jazz Poetry Concert, said this year will be different because he gets to perform with the quartet. In previous years, he performed solo and with a local rhythm section.

"This is a wonderful event," said Lake, who is also a poet and painter. "I get to work with poets, and that's special for me. But I also get to perform with the band."

When the quartet takes the stage, Lake said the group will mine its discography for old nuggets as well as perform pieces from "Political Blues," their latest recording.

"We were looking to make a political statement with this one," said Lake, who said the band had never previously recorded a politically charged album. "This is something that Max Roach and Abbey Lincoln did in the 1960s. We were inspired by that but also by the current political situation, particularly as it relates to New Orleans and the war in Iraq."

The World Saxophone Quartet has come a long way from its roots -- Lake said it started out almost accidentally.

The four original members were living and performing separately in New York when New Orleans saxophonist Ed "Kid" Jordan invited them to the Crescent City to perform, Lake said.

"Ed came to New York, and he wanted to bring each of our groups to New Orleans, but he couldn't afford to do that, so he asked if the four of us could come and he would pair us with a local rhythm section. We went there, and honestly we were nervous. We didn't think the crowd was going to enjoy the music. The response to the first concert was so incredible that we decided to keep the group together."

When the quartet returned to New York, they tried to find the appropriate rhythm section but were unable to agree upon one.

"We went with just the four saxophones," continued Lake. "We did our first gig at a place called the Tin Palace, in the Lower East Side. And we've been going ever since."

During the early years, Lake said Hemphill was writing and arranging most of the music.

"He provided the sound that we started out with," Lake said. "He was an incredible composer and had a way of voicing the instruments. When you heard a piece of his music, you knew it was Julius. He covered the spectrum in his music and wrote to the strengths of each member.

"When we started out everyone was very strong individually. That was great because when we took a solo, it was very strong. I think that was one of the things that made the group unique, in addition to the types of tunes we played."

After Hemphill left the band, Lake, Murray and Bluiett began to share the writing responsibilities.

"We still have our signature sound," Lake said. That cutting-edge sound is characterized by group improvisation like few others.

To get a feel for what that sound is like, all you have to do is listen to "Hattie Wall," the group's theme song written by Bluiett nearly 30 years ago.

"That song embodies how all of us approach the music of the group," Lake said.