Every artist has the right to evolve, to advance his or her talent, to obey personal aesthetic zenith.

Unfortunately, in pop music, most, in fact, the vast majority find a comfortable niche that sells records and tickets and fade eventually into some artistic graveyard. There are always battalions of new, cliche-ridden pop stars ready to throw on that last shovelful of oblivion.

Alas, there are some who do recognize the importance of growth, even if that means becoming less immediately accessible or may prove unpopular to fans.

Joni Mitchell can be regarded as one of these whose aesthetic judgment takes precedence over popularity.

When she appeared here several years ago with the Tom Scott LA Express, I felt she was trying to be just a little bit hip, leaving her folk music roots for a semblance of jazz that might curry favor with critics.

Wrong. With her new tour and album, she's taken on a project associated with jazz that has gone to the very soul of the late Charles Mingus, with whom she collaborated before his death.

The results came to Portland in a live show Monday night in Memorial Coliseum with about 8,500 fans looking on. Her efforts proved to be truly genuine, musically, lyrically, and in the choice of musicians backing her. A six-piece band made up of some of the finest young jazz and fusion artists playing today.

Ms. Mitchell hasn't left her guitar-and-vocals totally behind; she's advanced her music into new areas, writing new lyrics and singing with what seems more grace than before.

The concert was more than 90 minutes long and had enough variety to keep all but the most narrow fans happy. She opened with a series of songs from many of her previous LPs, including "Paradise," "Hijira," "In Summer Lawn," and a beautiful tune that began with the words, "No Regrets, Coyote."

The Mingus material was eloquent, occasionally complex and marvelously heady. Her lyrics to the legendary bassist-composer's music were occasionally hard to pick up in the sound vacuum of the coliseum, but the backing band was not. Much of it was biting, some humorous, including "God Must Be a Boogie Man," a piece that had a "gospel" vocal from some of the band playing percussion instruments.

Ms. Mitchell's vocals have taken on a new smokiness and definitely reflected her study and apparent appreciation of jazz singers such as Billie Holiday, Annie Ross, Jackie Moss and others.

There were many highlights in the show. One, a contemporary piece of electronic music by bassist Jaco Pastorius, was excellent. Another tune featuring guitarist Pat Metheny was a wistfully long appreciation course in meaningful guitar that didn't have to resort to flashing, flying fingers.

After several trips into new sounds, she returned to play solo again, getting later into some wispy effects with saxophonist Michael Brecker, a musician whose tenor and soprano solos were driving and forceful looks at jazz.

Ms. Mitchell finished the concert with a couple of tunes with the Persuasions, five singers who accomplish a cappella singing like no one. The six singers were abetted by some vast chording on organ and the sound was quite "churchy." Very interesting.

The Persuasions opened the concert with a beautiful set of "street corner" music that had some of the crowd up front to sing on "Tom Dooley" and dance to other songs.