
The skill behind the cartoon is credited to two different people. The first saxophonist to be the chops for Lisa was a man named Kim Richmond. Richmond is a professional saxophonist as well as a composer. He played in the Air Force Big Band and arranged the California Jazz Orchestra to perform his own pieces.
The second man to play for Lisa is Terry Harrington. Not only does he play as Lisa, he writes (or improvises) her solos in various episodes.
The actual music that Lisa (or in reality, Harrington) plays is all jazz and blues. The intro to the show has some of Lisa's sax playing in it, which is distictively blues-y. Also, some of the solos she does are simple blues chromatic scale. In many of her solos, she plays very techincally, adding triplets to the jazz and blues scales many of her solos are based off of. And since this is a comedy cartoon, many of the solos are silly, like loud shrieks or playing off rythym on purpose. In fact, when Lisa plays horribly, blatting and off-rhythym, Homer says "Now you're swinging honey!"