Prom 66: Cameron Carpenter, Royal Albert Hall, London ***; Prom 69: Leipzig Gewandhaus/Chailly, Royal Albert Hall, London *****

The young American organist Cameron Carpenter proclaims 'I'm not the next Liberace - I'm the first Cameron Carpenter'.

He's certainly more interested in music than Liberace was, and he's made a speciality of styles which would make your average organist’s hair stand on end. In his view organists are the enemy: every one of them, he told Front Row last week, must decide 'if he's going to be an entertainer, or remain a specialist' - as if the two were mutually exclusive.

His great sorrow, he said, was that stuck up in the loft he couldn't be seen, and when he pranced on to deliver his take on Bach - with Mohican hair, singlet and spangled tights, and (below the visibility line) rhinestone organ shoes - one realised how deep that sorrow was. The rhinestones did some very fancy footwork in the first Toccata and Fugue, which veered between faint and deafeningly loud, and banished any thoughts one might have harboured about structure, finesse, or beauty: ending with a dainty little flourish on the celeste stop, this was Bach refashioned for the fairground. Interlarding his Proms recital with camp repartee which made his Radio 3 interlocutor sound desperately stuffy, he then treated us to more of his effects, the favourites seeming to be trumpets, kazoos, parps (as from the horn of an articulated lorry), and distorted clarinets recalling the sound we kids used to make by blowing across two blades of grass. His stop-armoury simulates a bunch of cabaret musicians in mutinous mood; his improvisations blend jazz, swing, 'Rule Britannia', and 'Chariots of Fire'.

So where did this leave Bach? Well, Bach can survive any assault, and was himself a great re-arranger. But you miss the point if you ask how 'good' an organist Carpenter is. If this Bobby Fischer of the organ sends us back more demandingly to the 'specialists', he's done music a good turn.

Taking the stage which the Berlin Philharmonic had just vacated, Riccardo Chailly and the Leipzig Gewandhaus Orchestra demonstrated a different kind of excellence: in place of the Berliners’ patina, we got an account of Mahler’s Sixth Symphony which was blazingly visceral down to its shattering final chord. And under Chailly’s baton, Messiaen's 'Et exspecto resurrectionem mortuorum' became a majestic chain of musical thoughts, each one presented in marmoreal grandeur.