You wouldn’t immediately tag the baritone Simon Keenlyside as the British singer most likely to don black tie and waltz into operetta. This is the baritone, remember, who took on Prospero in Thomas Adès’s opera The Tempest, who sings with muscular expression, not the vocal equivalent of the soft-shoe shuffle.

Yet here he is, partnered with another K, Angelika Kirchschlager, in My Heart Alone, a lusciously recorded twirl through familiar European operetta territory, with duets and arias from six composers, Lehár and Emmerich Kálmán predominating.

How does he manage? I hate to summon the word “adequately”, but when he’s pressed against Kirchschlager’s lilting vocal pearls, let alone rivals in history such as Hermann Prey or the golden tenor of Richard Tauber, you must admit, with regret, that he does come up a little short. Though he shapes and shades lines with refinement, there always seems something lacking: genuine warmth, a sparkle, the sense of being at home.

Keenlyside sings operetta like a student, learning the ropes, too quick to pitch volume and intensity at a level fit for Verdi, but not the sweetmeats of Vienna. In The Merry Widow do we want a Danilo who bellows? Not really. Still, bless the fellow for trying, and for willingly embracing repertoire that people too easily mock.

Best to concentrate on the other K, who is frequently marvellous. As an Austrian, the operetta lilt lives in Kirchschlager’s blood; she’s a natural at pausing and easing the speeds, and she sings with that indefinable glow. In duets such as Mia bella Florentina, one of two selections from Suppé’s superb Boccaccio, she outshines Keenlyside rather brutally. From her solo numbers, it’s hard to pick which is best: her tender Viljalied, perhaps, or the twinkling Meine Lippen from Lehár’s Giudetta.

Accompanying, Alfred Eschwé and the Tonkünstler Orchester Niederösterreich sweep along with a light touch fleetingly compromised by some overinsistent plucked bass lines. As for the selection, it’s safe and wise, though Kálmán sounds kitsch after Suppé, and I missed Leo Fall, a neglected “Silver Age” master whose melodies can turn iron constitutions to jelly.

And a brickbat to Sony Classical for being so cavalier with the documentation. There’s no setting up of each selection, no song texts. These things matter, even in operetta.

(Sony Classical, TMS £12.99, call 0845 6026328)

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