Cecilia Bartoli/Il Giardino Armonico, Barbican Hall

Cecilia Bartoli’s latest album and road show – "Sacrificium – La scuola dei castrati" – comes courtesy of an era characterised by the unkindest cuts of all. The composers' names are all but forgotten but those of the genitally compromised superstars are not. We have heard only simulations of the kind of sound these surgically adjusted males could produce but from all the documentary evidence it was bigger and more pungent than the undeniably engaging Bartoli is apt to produce. But where she does share a certain kinship with the castrati is in her ability to make a three-course meal of second-rate music. The album, the concert, was choc full of it.

So enter the popular Italian diva done up like Dick Turpin in tatty pantomime garb – swishing cloak, thigh-length boots, and plumed hat hurled theatrically across the stage to launch her into the first of a succession of bravura arias, this one by Nicola Porpora (remember him?). Bartoli’s way with coloratura is a little too close to yodelling – or even gargling when the sound is so far back as to have you wishing you could reach out and pull it forward. And all the while her diaphragm is working overtime to achieve the aspirated "rapid-fire" effect of the passage-work.

Who knows how the castrati of the day sang it but any singing teacher will tell you that this is definitely not a healthy way to sing this repertoire. On the other hand Bartoli is able to achieve a dazzling degree of punchy rhythmic precision that would not otherwise be possible. And in the closing number of the first half she picked up on the fizzing virtuosity of her “band” – the stunning Il Giardino Armonico – mimicking the explosively accented string dialogue and thrusting natural horns with terrific aplomb and hitting the Italian consonants like grenade attacks on the text. It was engaging and it was thrilling but more by virtue of Bartoli’s boisterous personality – legs butchly astride, jaw jutting defiantly – than the impact of her voice.

The fact is there isn’t a lot of voice and when swallowed in the way I have described, and without the scrutiny of a recording microphone, it can resemble the clucking of an overanxious hen. But artistry such as Bartoli displays can make you forget and forgive the more freakish aspects of her coloratura singing and when she slips into the lyric numbers and floats a plaintive romance it can be quite ravishing. Numbers like the trill-festooned "Qual farfalla" from Leonardo Leo's Zenobia in Palmira or better yet "Misero pargoletto" from Carl Heinrich Graun's Demofoonte were riveting for the wealth of expression she was able to invest from so little capital, so to speak. In the latter aria, the plaintive lamentation was produced from so little air passing over the vocal chords that phrase lengths could be eternal. Il Giardino Armonico provided an exquisite cushion of sound on which her voice could recline.

She saved the damsel in distress until last – Porpora's Adelaide – weathering the storm over two octaves and more reminding us as she hit rock bottom of the contralto range that this damsel was once a chap.