On Quartet, Pat Metheny and Brad Mehldau exhibit the kind of unspoken chemistry of two musicians who have been collaborating for years.

But in fact the two jazzers had never made music together until last year's Metheny/Mehldau. The 2006 release brought together iconic jazz-guitarist Metheny, 53, and rising jazz-pianist Mehldau, 37, for a stellar album of original material.

The pair had long admired each other before working together. Mehldau first heard the Pat Metheny Group's Travels album (1982) at 13 and Metheny heard Mehldau's piano chops on saxophonist Joshua Redman's 1994 Moodswing. With shared admiration, the two finally decided to play together after they both signed to Nonesuch. Their 2006 collaboration proved an important addition to the label's catalog, merging a jazz legend and a poised-to-be one.

Metheny and Mehldau's collaborative creativity rises to a new level on Quartet, where boundaries are played with, stretched and challenged via tempo and mood shifts. Bassist Larry Grenadier and drummer Jeff Ballard, who have played in the Brad Mehldau Trio since 1994 and 2005 respectively, round out the solid four-piece sound.

The album opens with "A Night Away," which establishes the four musicians' superb balance and tight sound. Ballard's beat is ocean-like, with rolling drums and spontaneous cymbal crashes. Mehldau and Metheny play off each other's melodies - something they will do throughout the rest of the album - and display a keen perception of one another's improvisational styles. The first half of this eight-minute track is dominated by Mehldau's complex chromatic lines, but Metheny takes the reigns in the last four minutes, displaying a flurry of fast and controlled melodies.

Each subsequent song brings yet another mood to the album. "Sound of Water" starts with Metheny imitating falling water with a sparkling, descending glissando. Mehldau follows his lead, echoing on piano. It's a symbolic moment - Metheny guiding and making clear the mutual, musical trust built between him and Mehldau in only a few short years.

"Fear and Trembling" exhibits Metheny's versatility, producing frighteningly dissonant intervals with a bright, erratic tone. This track's disturbing, scream-like twangs invoke the disorientation of fun-house background music.

"Towards the Light" is the biggest achievement in Metheny and Mehldau's collaborative body of work to date. Mehldau plays an almost atonal improvisation in hemiola with Ballard, while Metheny solos using a bright, brass-like sound. A distortion-packed rock section materializes from nowhere, but the head-banging frenzy dissipates back into soft jazz before you can fully comprehend its tonal scope. The fluid shifting of moods, qualities and tempos in this piece comprises the most imaginative Metheny/Mehldau statement yet.

It's already clear this album goes beyond any of the Pat Metheny Group's previous records because of its sheer dedication to spontaneity and experimentation. Quartet is fearless in its musical exploration. Metheny and Mehldau's creative capacity and ability as well as desire to search continually for original sounds makes this collaboration, and hopefully future ones, a significant contribution to jazz.

Four Stars out of Five

Pat Metheny and Brad Mehldau
Quartet

Nonesuch