But, in fact, the new organ is a real challenge; here are all the problems raised by the movement towards "authenticity" in the most extreme form. This instrument is not merely an electronic "Bradford" organ with 80 loudspeakers decorously concealed behind the Victorian organ-case housing the now redundant pipes of the old "Fr Willis" instrument. On the advice of Simon Preston, a former organist of Christ Church and Westminster Abbey, the organ-maker Wood & Son has installed three complete organ specifications, based on Salisbury Cathedral, Pembroke College, Cambridge, and St-Clotilde in Paris.
Preston himself showed off all three on Saturday with the Oxford University Orchestra conducted by Sir Roger Norrington. The orchestra began with a lively, vigorous account of Handel's Fireworks music. Worries began with Preston's first solo organ piece - Bach's great G Major Prelude and Fugue. The higher registers were bright enough, but the big pedal diapasons completely lacked the punch of a real organ. Much of it had the slightly hazy quality one associates with English cathedral sound. Perhaps we should wait for the installation later this year of a fourth specification, "North German Baroque", which hopefully will sound something like the instruments used by Bach.
Far more successful was Purcell's D Minor Double Organ Voluntary, played on an approximation of the little chapel organ at Pembroke College, Cambridge. This instrument is by "Fr Smith", the German organ-builder Bernhard Schmidt who added the first little organ to the Sheldonian in 1671. The sounds were indubitably authentic, but I'm old enough to miss the clatter of the keys. More acceptable by far was a recently rediscovered Allegro, Chorale and Fugue by Mendelssohn, played on the Salisbury "Willis" instrument, the Chorale sounding solid without a "churchy" heaviness.
Where the concert took a really alarming turn was in the works played on a replica of the vast St Clotilde organ. Inevitably Preston played some Widor - an innocuous Allegro from the Fifth Symphony rather than the well-known Toccata, followed by the Sinfonia Concertante by the Belgian composer Joseph Jongen. This dates from 1926, though you wouldn't think it from its firmly 19th-century idiom, alleviated by occasional nods to Ravel and Debussy (even, if I'm not wrong, the odd passage of discreet atonality). Doubtless this was one of its rare revivals, and frankly a more inappropriate setting could hardly be imagined. Surely an organ is part of the ambience, if not the very architecture, of the building it serves?
Wren's original Sheldonian design has no organ at all - but if we are to install a "Bradford', surely the building cries out not for Jongen, but for a couple of Handel organ concertos - almost contemporary and among the few really great secular works for organ and orchestra.
Listening to the Christ Church organ the following Friday (the "Sacred Songs" concert in the Oxford Contemporary Music Festival), revealed the limitations of the Sheldonian instrument yet more clearly. Even Ekki- Sven Tuur's Spectrum 1, a challenging, post-serial work owing not a little to Ligeti and Xenakis, was based around the note C - here expressed by a sustained diapason sound that appeared to emerge from the bowels of the building. Equally, in Arvo Part's When Sarah was Ninety Years Old, the ecstatic organ outburst at the moment of Sarah's conception would have been inconceivable on an instrument like the Sheldonian's. This dramatic interjection comes after an interminable period of waiting. Only regular drum-beats and passages of wordless melisma by two unaccompanied tenors (Alexander Massey and Brian Chapman) indicate what seems to be an ever slower passage of time. Then, as the miracle happens, the organ bursts in and the soprano voice rings out in triumph from high in the organ loft.
The last work consisted of a complete Mass sung by a capella soprano - Naji Hakim's Missa Resurrectionis (1994) - with the five movements of Messiaen's Messe de la Pentecote played on the organ at appropriate moments. Hakim's setting, sung with utmost dramatic force by Helen Meyerhoff, induced intense concentration on the words. Messiaen's static, often massive, note-clusters guided the mind in parallel meditations. As so often his birdsong, here during the Communion, came with the sense of a true gift from heaven. The birds sang again in the final Recessional, between passages in which the full organ - at a volume which the Sheldonian's "tasteful" instrument would never dare attempt - brought us the "rushing mighty wind" of Pentecost.