In a recent interview Elton John conducted with Elvis Costello, the rejuvenated John (whose two-decade slump ended three years ago when he once again tapped into the spirit of his early, best, music) said this: "With certain older records you can't even describe what it is that makes them sound so unique, whether it's the studio or the group of musicians. Those elements just had a way of working in conjunction with one another."
As with the finest records, there's an ineffable alchemy at the core of the best shows which comes to define them. You can point to a high standard of playing or songwriting or sound and say that's why it works. And you'd be half-right: the cerebral half.
For example, quite aside from Elvis Costello's songwriting, the band he has now can play pretty damn well by any criteria.
Drummer Pete Thomas and bass player Davey Farragher do everything necessary superbly with not a superfluous, grandstanding note more, while Steve Nieve is an often astonishing whirl of improvised organ runs, electric piano stomps, theremin squalls and delicate spirals.
But what marks them out in concert now, three years into their partnership (when the American Farragher joined the long-established English trio) is feel. Over and around the brain of these songs is the blood, bone and sweat of a group so in tune with the music and each other that matters flow without thinking.
And that's true whether it is rugged as in the thumping simplicity of "Uncomplicated" and the slashing pinpoints of "Needle Time," very danceable as in "13 Steps Lead Down" and "I Can't Stand Up For Falling Down" or more sensitive as in the delicacy of "Heart Shaped Bruise" (coming out of a lovely "Good Year For The Roses" and featuring "Daveylou" Farragher standing in for Emmylou Harris on backing vocals) and "Nothing Clings Like Ivy."
In the company of a new batch of songs steeped in, but not simply beholden to, the basics of rock 'n' roll in post-war rhythm and blues and unfussed country, this approach makes Costello's less refined guitar playing - where angularity, tone and absence where necessary are key - not just appropriate but vital.
It also positively encourages moves such as the rolling thunder of the uninterrupted opening four songs (which climaxed in a throbbing-vein-in-the-temple version of Radio Radio); the perfectly judged Johnny Cash walking rhythm of "Hidden Shame" (which Costello wrote for Cash) alongside the southern soul touches in "Either Side Of The Same Town" and Peter Green's "Love That Burns"; and the pairing of Dave Bartholomew's 1954 New Orleans stomper "Monkey" with its "answer song", Costello's own "Monkey To Man."
To get this energy and thought matched by feel meant that this 30-plus song, 2-hour show, including an hour-long encore which was in effect a more energised second set, never felt anything but pulsating. It was a great rock (and country, and rhythm and blues) band playing great rock (and country, and rhythm and blues) songs. Sounds simple doesn't it? Hardly.