What makes a performance release-worthy? There are those who would like to see any recordings made by an artist released in some fashion, and with the advent of digital downloads there are artists doing just that. Still, just because it can be done doesn't necessarily mean it should. While greater discretion is undoubtedly a good thing, having released the mammoth ten-LP (now six-CD) Sun Bear Concerts (ECM, 1978), it's clear that pianist Keith Jarrett is bold enough to buck marketing trends when he feels the music warrants it. It's been over 25 years, in fact, since Jarrett last released a multiple performance box set of solo piano improvisations—the three-LP Concerts (ECM, 1982), still awaiting full release on CD—but he clearly feels the music on Testament - Paris / London deserves to be heard. Based on these two performances, recorded five days apart in the fall of 2008, it's hard to argue with him.

Since returning to solo performance earlier in the decade, Jarrett has shifted from the continuous, near-stream-of-consciousness style of Sun Bear and classic The Köln Concert (ECM, 1975) to the shorter, but conceptually connected improvisations of Radiance (ECM, 2005) and The Carnegie Hall Concert (ECM, 2006). While it's still about grabbing music from the ether, there are a number of defining markers that can be expected in almost any Jarrett performance: oblique and often dramatic classicism; the occasional overt jazz reference, often via bop-inflected lines and even the occasional stride reference; tender, economical lyricsm; hints of gospel, Americana and blues; and hypnotic, ostinato-based soloing.

In the hands of almost any other pianist, having such well-defined stylistic signposts might result in redundancy, but it's a testament to Jarrett's remarkable talent that each performance sounds fresh; distanced from each other but coming, unmistakably, from a single voice. Despite pauses between the eight parts that make up the 70-minute concert from Paris, and the twelve-part, two-disc set of improvisations from the 93-minute London performance, the pieces come together as a narrative whole, with each night distinct in its emotional arc. Both performances begin in relatively dark territory, but the Paris show quickly turns frenetically free, while London remains sparer and more profoundly emotional, with Jarrett's vocalizations a clear channel from his ears to his hands. That London ultimately turns to similar turf in "Part II" only contributes to a performance that speaks in Jarrett's distinctive voice, but unfolds in a different fashion.

The manner in which the two concerts end is another indication of how, despite personal qualities that can't help but surface, Jarrett is absolutely working without a roadmap. After the Americana-tinged penultimate part, Paris ends in something of a return to the frenzied contemporary classicism of its opening; London, on the other hand, moves through three final movements that start with a pulsing ostinato that alternates between 3/4 and 5/4, gradually building only to dissolve as it moves into the closest approximation of a jazz ballad, only to end with a buoyant taste of the gospel roots that are one of Jarrett's many foundations.

Why one night is so fundamentally different from another is likely a combination of factors—some significant, others mundane, but all of which are internalized into an indescribable something that ultimately takes form when Jarrett hits the stage. Testament - Paris / London is yet another high water mark for Jarrett, and all the more remarkable considering how many solo performances he's already released. We may never truly know why Jarrett chooses to release one concert over another, but as long as he continues to deliver performances this stellar, perhaps it's a question that really doesn't need to be answered.

Tracks: CD1 (Salle Pleyel, Paris: November 26, 2008): Part I; Part II; Part III; Part IV; Part V; Part VI; Part VII; Part VIII. CD2 (Royal Festival Hall, London: December 1, 2008): Part I; Part II; Part III; Part IV; Part V; Part VI. CD3 (Royal Festival Hall, London: December 1, 2008): Part VII; Part VIII; Part IX; Part X; Part XI; Part XII.

Personnel: Keith Jarrett: piano.