One of the consistent joys of seeing a performance by the Royal Academy of Music's opera school is that they bring in world class conductors. At last night's La vera costanza, the orchestra, conducted by Trevor Pinnock, was exceptional. The whole evening's music was played with sprightly elegance, lightness of touch and perfectly weighted changes of pace and strength as the music shifted moods between comedy, pathos and storm-laden drama. Haydn's sense of humour came through especially clearly: the music is infused with a sense of joy and fun.

La vera costanza is a light romantic comedy with a happy ending: our heroine Rosina is a common fisherwoman who has been secretly married to the tenor, Count Errico, who has abandoned her and shows signs of being, er, barking mad. The Baroness is trying to marry Rosina off to the soft-headed bass, with added interest from Rosina's brother, the Baroness's lover and the Baroness's maid. The resulting action is sufficiently batty as to defy any attempt at synopsis but is easy and pleasant enough to follow when you're seeing it on stage. It provides a suitable backdrop for the traditional set pieces of Italian opera: individual arias, duets, trios and some sparkling ensemble numbers, all kicked off by a shipwreck scene in which Haydn can display his sturm und drang abilities to great effect.

In no uncertain terms, the piece provides a vocal workout for its cast. The vocal lines go through all manner of jumps, swoops and changes of pace, and I was very much aware of how much was being demanded of young singers: diction, accent, intonation, phrasing, balance, dramatic intensity. La vera costanza is similar to Mozart operas in overall nature, but it seemed to me that the vocal lines don't fall as naturally as they do in Mozart and the singers were being required to do a whole lot more work to give their arias the desired lift.

Broadly, this was a strong cast who made a very good fist of it. Diction was excellent: although this is the first time I've seen the opera, I could get away for most of the time without reading the surtitles (although the Italian accents needed some work, with the odd estuary vowel creeping in uninvited). But everyone was well capable of producing sound that was lovely to listen to while also making something out of their character, and the ensemble numbers were in perfect balance and generated real excitement. Acting was also generally good within the limitations of the roles which are somewhat caricatured.

Credit goes to all seven singers, with the most impressive (for me) being Rosalind Coad as the Baroness. Immaculately costumed, wigged and made up to look like a Meissen porcelain figurine, she produced a light, breezy coloratura well capable of a steely edge when hitting the high notes without ever going brittle. As Rosina, Helen Bailey has a difficult role in which she is required both to be the butt of comedy and also to lift proceedings to a more serious level with a bit of genuine pathos: she made a fine effort at this without ever completely lifting me out of my seat, which Stuart Jackson did succeed in doing for Errico's aria in Act II when he is musing on whether to go back to his faithful wife.

Director Jamie Hayes and designer Tim Reed produced a setting that was simple, fun and effective. Masked stage hands manipulated a simple wooden structure to serve as ship, fisherman's landing or grassy bank, movement was good and period costumes very good. There were plenty of nice comic touches: I loved the moment when, after the interval, we see the fisherman Masino dangling a fishing line hopefully into the orchestra pit and the surprise on everyone's face when he reels in a violin.

What lets La vera costanza down is Pasquale Anfossi's libretto. It's not the most inventive or poetic, and I did eventually get fed up with the number of times when characters turned to the camera to explain that they were amazed, trembling, having palpitations, didn't know what to do next or generally needed advice or assistance from the heavens. Haydn's wonderful music makes it all worth listening to in spite of this, and Hayes did a manful job of providing visual and acting interest to cover the resulting dramatic hiatus, but by the middle of Act II, the production was beginning to run out of ideas. It made me wonder what Haydn could have achieved with a librettist of Lorenzo da Ponte's class rather than Anfossi.

So plaudits to Royal Academy Opera on two counts. Firstly, despite the libretto, I'm glad to have seen this rarely performed work: the overall opera has genuine charm, and the music is really lovely. It's also interesting as a marker for the historical development of opera, containing both Handelian da capo arias and some early examples of the cavatina/cabaletta style that would be so popular in the early 19th century. Secondly, La vera costanza was a brave showcase for their singers, who rose to the challenges of a difficult piece. It was an interesting and enjoyable evening.