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Let’s acknowledge, right from the outset, that Kurt Elling commands a dizzyingly brilliant vocal technique.

Sure would be nice if he used it.

Not that Elling didn’t show flashes of inspiration Friday night at the Old Town School of Folk Music, where he sold out the first of two shows. His high-flying scat singing – though delivered in tiny doses – remains a marvel of technical acuity and improvisational daring.

This is the work that caused a stir when Elling first emerged as a vocalist in Chicago, in the early 1990s. Similarly, his vocalese – the art of applying original lyrics to already conceived instrumental solos – marked Elling as an artist with something freshly original to say. Here was a jazz musician doubly endowed with remarkable vocal prowess and obvious intellectual firepower.

In recent years, however, Elling has slowed everything down, preferring unhurried tempos, long-held notes and nice ‘n’ easy phrase-making. A sense of middle-age contentment defines much of his music these days, which clearly makes matters easier on his instrument. But it doesn’t quicken the heart.

For his current tour, Elling is singing work from his newest recording, “The Gate” (Concord), which shows Elling in supple voice but leaning toward low-key, slow-burn, pop-tinged crooning. Yet Elling – a jazz singer at his core – may not be the ideal interpreter for songs of Stevie Wonder, King Crimson and Earth, Wind & Fire.

His jazz-lite versions of this music cling closely enough to the originals as to pale alongside them. Inexplicably, he doesn’t transform these tunes as thoroughly or as boldly as the art of jazz allows.

As a result, one hears dutiful, mildly embellished, well-sung covers of overly familiar music. You can admire Elling for pushing beyond conventional jazz repertoire while regretting the mostly bland, warmed-milk quality of the results.

At the Old Town School, Elling generally put a high sheen on long-lined melodies that barely taxed his vocal resources. Though this music proved livelier than on the generally soporific new recording, Elling’s sequence of easy-breezy nocturnes ultimately induced drowsiness.

His plodding version of King Crimson’s “Matte Kudasai” preserved the luster of his voice but proved rhythmically stagnant and melodically dull. His fat, cloying vibrato on Earth, Wind & Fire’s “After the Love Has Gone” was not exactly a model of elegance and grace (though it’s even more egregious on the recording). And his account of Lennon and McCartney’s “Norwegian Wood” was unnecessary.

Still, there were high points in this set, which featured evocative accompaniments from pianist Laurence Hobgood, drummer Ulysses Owens and bassist Harish Raghavan.

In Wonder’s “Golden Lady,” Elling briefly cut loose with fleet, thrilling, mercurial vocal flights, each heightened by guitarist John McLean’s pungent responses. Elling’s vocalese on “Samurai Cowboy,” based on music of Marc Johnson, hinted at the glory days of Elling’s youth. And “Dedicated to You,” from Elling’s Grammy-winning CD of the same title, showed more urgency than on the recording.

Overall, however, sparks were in desperately short supply, as Elling’s music faded into the night.

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