Academy of Ancient Music/Hogwood, St John's, Smith Square, London

"Are my ears on wrong?" Charles Ives once plaintively asked when nobody seemed to hear his music the way he did. Surrounded by a large and enthusiastic audience including many of the musical great and good for the Academy of Ancient Music's visit to St John's, Smith Square, your critic continually caught himself agonizing over this very question.

It was not so much the mechanical beat, the scrambled tempo and the minimum of phrasing with which Christopher Hogwood propelled his players into the opening Allegro of Mozart's Symphony No 35 in D Major ("Haffner") K385. Such characteristics have been part of the AAM's "authentic" philosophy these 30 years, even if they now sound less redolent of "cleaning off the varnish" than of limitations in Hogwood's own musicality.

What distressed this pair of ears was the orchestra's instability of pitch and intonation – its persistent "distonation", to borrow Hans Keller's useful term. Despite tuning to the fortepiano, the wind section sounded recurrently sharp of the strings throughout Moz-art's long and stormy Piano Concerto No 24 in C Minor K491, while not even that lively soloist, Robert Levin, could compensate for the fact that his instrument sounded flatter still. Granted, period instruments are specially vulnerable to atmospheric conditions, but the AAM is stuffed with experienced players well able to make interim adjustments. Could it be that, as a body, they have gone too long uncorrected because their conductor simply does not hear anything very wrong?

Levin, an engagingly impulsive player behind whose historically-informed cultivation of the Viennese Classical repertoire one suspects a post-Lisztian Romantic rampaging to be let out, opened the second half with a lengthy improvisation on four randomly selected themes submitted by the audience. This proved more engrossing in short-term thrills and spills than clear and coherent overall, but then, even on the level of 18th-century clichés, the themes were pretty inept.

The programme culminated in a brisk rendering of Mozart's Concert Rondo in D major K382, and the finale of the "Haffner" Symphony, left over from the first half, because 18th-century practice sometimes split symphonies in this way. Hogwood then chose to overturn the latter touch of "authenticity" by conducting as his first encore, the March K408 No 2, which Mozart wrote to precede the entire symphony. After all this, your critic felt lonelier still amid the euphoria in finding the second encore, a cod-Figaro arrangement of Eddie Cantor's "If you knew Suzie", no joke at all.