Cassandra Wilson is the only jazz singer worth listening to these days, and now she’s not even a jazz singer anymore.

Whatever that means.

In fact, there have never been more fine jazz singers to choose from, but a precious few are serious about bringing something new to the art.  The danger is of the rock-and-hard-place variety: if you bring jazz singing into today’s music, it seems to become something else altogether, but if you don’t—you risk singing Gershwin less well than Ella for the rest of your life.  Cassandra Wilson has dared to leave the trappings of jazz behind, and yet her artful voice has somehow made the idea of “jazz singing” new again.

Thunderbird is the latest in a series of reimaginings of jazz singing.  Without question, it is Ms. Wilson’s furthest departure from the jazz nest, but it also ultimately proves that Cassandra can fly.  This record was produced by T Bone Burnett and is a clear break from the string of discs Ms. Wilson has made for Blue Note since 1993’s Blue Light Til Dawn.  Those records were dominated by a neo-folk sound of acoustic guitars and percussion—and they lilted gently and intimately on a mixture of Robert Johnson, Van Morrison, and various originals.  Both crystalline in sound and a bit junk-shop rough around the edges, records like Blue Moon Daughter and Belly of the Sun set the table for Norah Jones and were in sync with the resurgence of roots-folk artists like Gillian Welsh and Neko Case.

Thunderbird, in contrast, is dominated by scrappy-gorgeous electric guitars (Marc Ribot and Colin Linden), pop-hop drumming (Jim Keltner and Bill Maxwell), crisply synthed keyboards (Keefus Ciancia), and bass (electric by Mike Elizondo and acoustic by Reginald Veal).  Mr. Burnett places Ms. Wilson’s voice against a much more busy, more electric, more artificial field of sound.  But it is a smashing success because the production never overwhelms Cassandra’s trademark vocal style—her subtle bends, her swooping contralto, her wordless moans and cries—and because the tracks are punctuated by two magnificent vocal-guitar duets that quietly destroy the jazz vocal competition with the flick of a high-E string.

Thunderbird establishes itself as different from the first sound.  “Go to Mexico” begins with a sample that announces itself as such by stuttering the song into being.  “Hey Pocky-A-Way” (a Meters tune with the great rhythm section behind a black Mardi Gras “tribe”) isn’t exactly the usual JB sample, of course, and so this particular bit of hip-hop influence is still raggedly strange.  Mr. Veal and Mr. Keltner lock down the rhythm under the sample, and Ms. Wilson finds herself singing harder and higher than usual, telling a vague tale of entrapment and fantasized escape.  This album, it seems, is providing that escape.

After this rattling opener, the disc comes at you two ways.  There are five tracks that present themselves as idiosyncratic pop songs, and four tracks that trail their dirty roots in blues, country, and jazz across the album’s face.  The pop songs are dirtied-up and grooved, without nearly the prettiness of Ms. Wilson’s other Blue Note records.  Each one is a small treasure chest of musical details not to be missed.

Jakob Dylan’s “Closer to You” is announced by a series of atmospheric whooshes and keyboard plinks, followed by Mr. Veal’s acoustic bass and a Keltner pocket that is dry and tight.  Ms. Wilson sings the pleasing song without over-affectation (and even a little acoustic guitar of her own) and with a soaring simplicity.  “It Would Be So Easy” is even better, a funky set of licks that allows a series of incredible pleasures:  a double-voiced chorus (“Tell me that you love me / Tell me that you need me / Show me that you love me / It will be so easy”), a verse underpinned by Ribot’s hypnotic guitar, a spaced-out bridge over a few bars of keyboard swirl, a funky break for clavinet and acoustic bass, and even an out-chorus where the drums rave up some and take the tune home.  The closer, “Tarot”, combines looped percussion, lush background vocals, call-and-response on the chorus, and a hip harmonica solo by Gregoire Maret.  “Poet” contains a noisy breakdown in the middle that is the furthest thing from jazz—all distortion composed into rhythm and a two-note guitar figure.  “Strike a Match” has a psychedelic sound, alternating between a funky figure in 7/4 time and various hazy settings for Ms. Wilson’s voice that include strings and various keyboard sounds.

The other side of the records exhibits its transcendent take on more traditional music.  Willie Dixon’s “I Want to Be Loved” allows no argument.  Keb Mo guests with a tasty blues solo, and Cassandra eases her way through the vocal, making it all sound perfectly languorous.  “Easy Rider” is a true 12-bar blues, but its journey is unusually complex—an out-of-tempo pair of choruses with just the two electric guitars, two gloriously sloppy choruses with the full band rocking like gang of drunk geniuses, then a hushed chorus against only piano before a full band ending.  An exhilarating seven minutes.  “Lost” is a duet waltz with Mr. Ribot’s guitar, a delicate piece of minor-keyed wordplay and pleading.  It’s the jazziest tune on the record—something that lets Ms. Wilson carve out the melody and move through the changes like Billie Holiday in a reminder of where she comes from as an artist.

But the centerpiece of Thunderbird—its masterpiece too—is Ms. Wilson’s duet with Colin Linden’s slide guitar on “Red River Valley”.  That’s right: it’s an old cowboy song that the jazz diva ultimately spins into gold here.  Using the bent strings and vocal mannerisms of blues, the duo makes a ditty into a novel. Ms. Wilson and Mr. Linden take their time, sculpting the song in sound. Ms. Wilson takes the simplest of tunes and uses her invention to gradually build something complex, personal, and continually alive.  It’s the kind of thing you can climb around on for hours, in and out of its crevices, up and down its slopes.  That’s what makes her a jazz singer—no matter what style of music she may be singing.

It seems a fair bet that some of Ms. Wilson’s fans may find this record a sell-out or a betrayal of her “purer” style.  But Cassandra has never had a pure style.  She’s been morphing from the very start, finding different collaborators and allowing her art to be reframed and pushed in new directions.  Maybe it’s the most “jazz” thing about her—her Miles-ian restlessness.  Also like Mr. Davis, she has an always-identifiable sound that benefits from its collisions and fusions with pop music.

Thunderbird is the best work that Cassandra Wilson and T Bone Burnett have done in years.  It is jam-packed with invention.  It is something strange and something appealing—and something special.