A lack not of taste but of fire

Duets are a way of life for Emmylou Harris. She’s a veteran country-folk-rock artist with her own long history of solo albums and hits, but her soft, high twang is also much in demand elsewhere, recruited over the years to sing alongside the likes of Neil Young, Bill Monroe and, most memorably, Gram Parsons.

Harris’ newest singing partner is former Dire Straits frontman Mark Knopfler, whose vaguely Dylanesque growl makes a surprisingly fine counterpoint to her elegant understatement.

At the Gibson Amphitheatre on Wednesday, their voices mingled with ease during nearly two hours of romance and regret, even though much of the material lacked the emotional fire they deserved.

Harris and Knopfler settled mainly on songs from their new album of duets, “All the Roadrunning,� a pleasant enough collection of midtempo ballads. With a six-man band that included fiddle, accordion and Knopfler’s silver dobro, the results were always tasteful and too often enervated.

The album’s most moving song, Harris’ teary country ballad “Love and Happiness,� was left out of the concert, which was a shame. But the singers found needed adrenaline on “This Is Us,� their voices in tandem and set against the band’s atmospheric rumble.

Ironically, the two-voice concert got a subtle bolt of energy whenever Harris stood alone in the spotlight, beginning with her regretful “Michelangelo� and “Red Dirt Girl� (both from 2000), as she strummed an acoustic guitar to the faint backing of the band. Knopfler also delivered Dire Straits’ streetwise “Romeo and Juliet� in a stirring barroom whisper.

They closed the night’s second encore with a dreamy “If This Is Goodbye,� another of their finer moments at the Gibson and on the album and proof enough that this worthy collaboration requires only more material up to their potential.