This, the final indoor concert of the 2012 Edinburgh International Festival (the closing Fireworks Concert takes place under the Castle Rock in Princes Street Gardens), was bookended by possibly the loudest and quietest sounds in the festival.

Charles Ives' The Unanswered Question opens with a delicate mist of pianissimo strings. Having enthusiastically welcomed David Robertson to the podium, the audience settled impressively quickly and this delicate opening could be clearly heard in a packed Usher Hall. Throughout the piece the string harmonies are wonderfully peaceful and were beautifully controlled in this performance. With little in the way of discernible pulse, I was enjoying Robertson's minimal conducting when I noticed the beginnings of a very expansive gesture. He was, in fact, reaching behind to cue the solo trumpeter who was stationed, I think, in the Upper Circle (I was one floor below). This distance lent added poignancy to the five-note questions posed. What is the nature of the questions? Leonard Bernstein, in his 1973 Norton Lectures entitled 'The Unanswered Question' felt that 'whither tonality?' was at the heart of it. The five notes in themselves do not clinch any sense of key and bear little relation to the string harmonies – far less to the more agitated flute quartet whose counters constitute little in the way of an answer. I have loved this piece for many years and felt that this RSNO performance nailed its enigmatic nature.

For reasons I could only speculate on, the orchestra segued into Morton Feldman's Coptic Light, a work inspired by the composer's love of near- and middle-eastern textiles. Similarly meditative in mood, this is a much lengthier work; at around 30 minutes it dwarfs Ives' five-minute gem but could not be regarded as lengthy by Feldman's standards. Prompted by Sibelius' observation that, unlike the piano, the orchestra has no sustain pedal, this piece represents Feldman's attempt to explore the possibilities of such a phenomenon. Colours float around the orchestra in a audio-lava-lamp kind of way. The pointillistic texture appears to feature rhythm without pulse. By the end of this slowly transforming piece, I began to perceive puzzling off-beats in the woodwind but still really no beat in any conventional sense of the word. This is a mystery which requires further investigation. Unlike some seated behind me, who later claimed to be traumatised by the experience, I found it hypnotic and was quite unaware of the passing of time. One does become aware, in live performance, of the orchestral movement within the stillness, particularly in the percussion section whose sensitive mallet work contributed greatly to the work's glistening nature.

I was surprised to read in Michael Kennedy's programme note, that Walton's assured and explosively dramatic Belshazzar's Feast was his first choral work since composing some shorter works in his teens. Recounting the assassination of the idolatrous ruler, following the craven worship of several elements of the Periodic Table, it is rich in contrasting moods: the sorrow of exile; the pomp of the ruling and enslaving classes; unalloyed joy at the Belshazzar's dispatching after 'the writing on the wall' has found him wanting. The outstanding,180-strong Edinburgh Festival Chorus, honed by Christopher Bell, must have hit the 100dB mark on the word 'slain'. This word was all the more dramatic for being the lone choral sound in a baritone recitative – excellently delivered by Neal Davies. Considering the choral dimensions, the diction was very impressive and the balance in the 'Praise ye' passages was perfect. Lest it be thought that it's all about power and volume, this titanic chorus was capable of great delicacy, particularly as they expressed dejection by the waters of Babylon.

The RSNO were in tremendous form and special praise must go to the brass players. In addition to those on stage, seven additional players were stationed on either side of the Upper Circle. This use of space was very effective and, judging from audience reaction, was an element which many had enjoyed. Perhaps unsurprisingly, given the nature of the work and the forces involved, the measured minimalism of Robertson's earlier conducting, was replaced by a very much more dramatic style.

This really was a triumph on every level: an outstanding performance in itself, it was also a wonderful end to the concert and to the festival featuring, as it were, the home team, in great form, on home turf. There was an air of jubilation in the hall as the performers took their bows and I for one felt invigorated by the experience.