Joni Mitchell continues to evolve like some unfathomable yarn, in the process becoming one of the truly original and singularly unique singers around.

In a time when crazes and dazes abound, and glitter is in and pop music is into a drawn-out dead period, the long-haired Miss Mitchell continues to march very much to her own drum, ignoring cycles and latest in sound.

She started out by being a kind of fey-wispy-flower-child-folkie-in-a-bottle at a time when Joan Baez, Judy Collins, and to a lesser degree, people like Buffy St. Marie and Mary Travers of Peter, Paul and Mary were the top folk singers.

The image, and the sound was something soft and fragile, pretty songs from a high-pitched voice still evolving. The flower child stance was heightened by her album covers: simplistic drawings and paintings full of flowers and color. Writing the song "Woodstock" didn't hurt on bit either.

What has happened over the last year or so, especially with her last three albums, is a startling and radical departure.

What emerges is a kind of auto-biography, an ongoing story of past promiscuity, dead but sharply-remembered loves, pockets of time and feeling etched sharply, painfully and with a gifted eye for detail.

There is little doubt that she's writing about herself, about being who she is. What makes all that exceptional is that you do more than empathize. The words are at once poetic, ordinary and familiar. It is her happening, her feelings, her past and present, somehow transmitted to be ours.

On paper, the lyrics are a stark, often stinging recitation of the times of Joni Mitchell. The lady has obviously been somewhere and may even do it again.

".....but when he's gone...the bed's too big, the pan's too wide."

That's from "My Old Man", one of the songs on her album "Blue", from which I can't take out one bad song, one of those rare happenings on eight-song albums of any kind.

"Blue" marked, I think, the giant leap away from the waif and into the feeling woman, the inward trip that becomes outward art.

Some tart, sharp feeling entered into her songs, small notes of resignation, acceptance of desire and fear, ruminations on mistakes. And small portraits of singular lifetimes.

For instance:

In "A Case of You", she sings "...just before our love got lost you said, 'I am as constant as the Northern star...And I said, "Constantly in the darkness, where's that at? If you want me..I'll be in the bar'...."

It reads like a real conversation and it is territory (lost it again, why can't we get together. I hate you-I love you) that has been covered by other singer- writers, but never, I think, quite so on-target.

It doesn't read like much of a song, however, even when it's all laid out properly and in line. That's where the other side of her talent comes in, a side that is a little more difficult to pin down.

She has been called, quite correctly, I think, a jazz singer, by at least one critic.

it's as good a description as any, jazz meaning taking wild chances with phrasing, limits and boundaries, range and pitch, while some-how remaining in precise control.

Her voice can do things that most female singers don't even bother with. It makes, for instance, Barbara Streisand's attempts at holding notes, stretching vowels and feelings, seen at best only adequate.

Range is a lot more than noise and opposite ends of the scale. It's being able to take sharp turns in speed and pitch, as well as emotions, and making them quickly to fit a word, a thought or a feeling.

Joni manages, in the best of her songs, to sound at once bitter and loving, like a skipping pebble and a quickly-sinking, pain-filled rock. That she could touch all those bases within a single line or two is a measure of her talent.

Combining the voice and feeling with the writing is what makes her unique. But she leaves you with more than admiration. She manages, even when singing about places and parties that are unfamiliar, to stir and move your own past.