We're in the silly season - or at least a kind of vacation limbo - with a cultural quiz on Radio 3 at Sunday lunchtime chaired by Joan Bakewell, the come-think-with-me woman on your TV screen ever since the 1960s. Bakewell's other current show, Sound Choice, on Radio 3 at Saturday lunchtime, is more than entertainment, though it's that too. Having heard Siobhan Davies talk once or twice about the music she commissions for her choreography, I wondered how she would deal with something she wasn't selling - Bach's Toccata and Fugue in D minor. (Bakewell described it as possibly the most famous organ piece in existence. Like other iconic works of art, it may not be what it seems: it may not be by Bach and it may not have been written originally for organ.)

Davies and the tenor Robert Tear were given three recorded versions to compare without knowing who was playing. The discussion was introduced by a snatch of Ton Koopman's very striking version, though it was out of the subsequent running for reasons never explained. I would hazard a guess that the producer, Martin Cotton, thought it too personal and, perhaps, too specialised - many organ and early music buffs would recognise it instantly.

But first, Bakewell asked Davies and Tear what they would look for in a recording of this work. "Fantasy," said Tear, though he was probably thinking about the opening of the piece rather than the Fugue. "I'm going to say something really awful," squirmed Davies, and then admitted that she would look for a piano version, because the organ was too majestic and she found it hard to enter its world. She articulated exactly what many people feel about the organ, and showed perfect sense in preferring what has become the universal keyboard instrument, arguably the universal instrument full stop. Bach would have sympathised, since he was always transcribing music from one medium to another. Anyway, the first version left Davies feeling "outside its walls" - a vivid image for a performance she acknowledged gave a sense of architecture. She had another good image for an episode in the Fugue, which she described as like running up and down ladders before settling on a destination. Tear thought the organ in question might be "somewhere south of Paris" and felt that the player's rhythm lacked tension - which was like complaining that a Rolls Royce isn't nippy, because the recording was made somewhere north of Watford, on the huge main organ in Liverpool Cathedral. The player was Noel Rawsthorne, one of the most skilful organists of the older generation in this country, notable for his good judgement of tempo and rhythmic discipline.

Tear was really complaining about the instrument and the building rather than diagnosing the player's shortcomings. The version he liked best turned out to be by Lionel Rogg on an organ built by Bach's contemporary, Gottfried Silbermann, though both he and Davies were disconcerted by its birdlike harmonics - "tweeting", Tear called them. Davies preferred Peter Hurford's version recorded in Sydney Opera House, because it was the clearest and, for her, the most exhilarating. Tear thought it quirky, so that the Toccata was too clearly being read rather than following the logical flow of an improvisation. Which begged the question of whether improvisation is never elliptical, if improvisers never hesitate, change their mind or run up blind alleys. Finally, said Tear, you have to ignore everything except the musician who's playing. Yet the different qualities he and Davies pointed out were attributable just as much to the character of the instruments and the buildings which housed them. In the end, Davies's observations were more interesting than Tear's because she defined her terms of reference clearly and was disarmingly honest about the way she listened.

In the Proms Feature on Saturday afternoon, Michael Oliver asked whether the American composer Roy Harris was really a one-work composer or the victim of cruel neglect. You know the answer and, predictably, Sunday's Prom opened with his Third Symphony, the "popular classic" which has eclipsed 13 further symphonies and all Harris's other music. Still, I love those documentaries which bask in the warmth of seasoned witness - some came from Harris's widow - and Michael Oliver is a very confidential sleuth. Adrian Jack