Seven hours of attention, evenly split over two Proms, is a lot to ask of any listener, so that the pacing of the event becomes vital: here, variety was obtained through the careful juxtaposition of contrasting styles of music - and contrasting choirs, seven in a row between 2.30pm and 7pm, and 15 all at once at 8pm for Carl Orff's Carmina Burana.
The most consistently satisfying performances were given by Peter Broadbent's Joyful Company of Singers, who have been cleaning up choral prizes for a few years now. They began the afternoon, in tandem with another choir, Ex Cathedra, in a performance of that touchstone of the repertoire, Tallis's 40-part Spem in alium, soaring from initial hesitation into a thrilling tapestry of sound. Spem was not written for a building like the Albert Hall, of course: it needs a long, tall shape down which it can reverberate, not a huge space into which it disappears.
That problem affected other performances, some of them carefully considered, like those of the Choir of New College, Oxford, singing Taverner, Tallis, Stanford, Bruckner and Frank Martin under their director, Edward Higginbottom; they did not have quite the impact they deserved. Even the tougher textures of David Matthews's Vespers, extracts from which were given their London premiere by the Huddersfield Choral Society under Martyn Brabbins, had their problems: the organ's flowing contrapuntal accompaniment tended to drown the finer details of Matthews' vocal lines.
Still, there were some unqualified successes. The Joyful Company excelled themselves in Jonathan Harvey's Forms of Emptiness, which sets three poems by ee cummings, and texts, in droned Sanskrit and spoken English, from the Buddhist "Heart Sutra". The chorus is divided into three groups, each moving to a separate pulse - and it is surprisingly direct music from a composer with a reputation for intellectuality.
It was the interlopers in this feast of Vaughan Williams, Poulenc, Grainger, Charpentier, Monteverdi, Judith Weir and similar serious stuff, who pulled the biggest cheer from the crowd: the barbershop group, Shannon Express. There was some glorious hamming here: 40 green-blazered lads of all ages, swaying with the music and belting out showstoppers with absolutely precise intonation and crystal-clear diction that had a thing or two to teach their more earnest colleagues.
The evening's concert demonstrated the catholicity of our times: only the previous Sunday, in the annual Proms lecture (another Keynon innovation), George Steiner had condemned Carmina Burana as unequivocally Fascist music. That did not trouble the capacity audience, crowded into its half of the Albert Hall by the thousand singers who filled the stage and choir stands and spilled into the stalls - the largest number of performers ever to take part in a Prom. It was some sight, too: when Terry Edwards, the conductor, first brought them to their feet, the audience responded with a unison gasp. The small space left on stage was occupied by four pianos, ringed around by percussion, for a version of Orff's celebration of medieval bawdiness boiled down from the orchestral score in 1956.
Unsurprisingly, there were a few problems of ensemble (chiefly a tendency to land on the note first and then adjust the dynamic), though Edwards handled this huge mass of sound with easy confidence. He was rewarded with the kind of roar in France at the end of the World Cup.