Prometeo is a challenge to the faculty of listening; at least part of the meaning of its subtitle, ''tragedia dell'ascolto'', is that it is a tragedy to be perceived through the hearing only. It is a two-and-a-quarter-hour opera without staging or action, in which few if any of the words are intended to be distinguishable and whose dynamic level is often at the very limit of audibility. I was about to add ''and proceeds at a tempo of adagissimo almost throughout'', but even when, as often happens, the basic tempo is very slow indeed there are often two or more musics of different degrees of slowness going on at once, thus colour, texture and harmony change more rapidly than pulse. The effect, even so, is of a very long piece of very slow, very quiet music.
It is in nine sections; two of them give a clear indication of Nono's intentions. The fourth, Interludio primo, is for solo contralto, flute, clarinet and tuba, the instruments mostly doubling the voice, so that the whole piece can be heard as a monody in which the function of the instruments is to 'colour' the voice expressively. The text hints, with the aid of a single line from Hesiod's Theogony, at a vision of a new Prometheus. It was Nono's intention, I suspect, that having previously read the text (it is very short) we should perceive its meaning through the music alone. It is like a sort of ritual 'still centre' to the entire piece, inviting you to suspend your sense of time and listen to every change of pitch and timbre with an unaccustomed intensity: the musicians are instructed never to rise above ppppp, and in this performance they are admirably faithful to that instruction.
A different kind of challenge is posed by the sixth section, in which three very fragmentary 'movements', each for a different vocal and instrumental combination, are played simultaneously, punctuated by a separate chorus intoning six 'distant memories' from the Prologue. This time you will need the texts in front of you, since there are not three but seven of them and here they have fused with the music, as the voice and the instruments fused in Intermedio primo. The effort of hearing and making sense of three different, intermittent musical strands is great but already on a limited acquaintance I am aware of a strange poetry, a grave beauty.
One of the reasons for this is the extraordinary care with which Nono planned every aspect of what he called his 'acoustic dramaturgy', including its complex yet subtle electronic transformations. The setting of Holderlin interpolated into the third section of Prometeo, for example, is scored for two sopranos, two speakers, bass flute and contrabass clarinet, but the effect is not only of a hushed chorus, but of a chorus who magically move in space and recede from you as you listen: like many pages in this work it is a strange, beautiful ceremony.
The performance maintains a remarkable control over this huge span of hushed concentration. The recording, too, is exceptional, revealing gradations of quietness that I have rarely before been asked to perceive. Or has my hearing been sharpened by the experience? For that alone it would repay the extreme demands it makes of the listener, but its challenging redefinition of how music may encompass myth and drama (oh yes: you are aware of a compelling drama taking place, one which only your ears can interpret) is even more provoking.'