“To graindelavoix”, according to their website, “singers are ‘spiritual automata’”, whose voices “have no message anymore but rather are the pure expression of their underground: the gritty, intense and instinctive...” In an electrifying performance that was more passionate act of worship than concert, Belgian ensemble graindelavoix took this listener from the Kleine Zaal of the Concertgebouw deep into the uncharted territory of our own underground: the wilderness inside the heart, and the immense space that lies inside a moment.

The ensemble, led by director Björn Schmelzer, performed vocal music from 15th-century Cyprus: sacred polyphonic music for Christmas by composer Jean Hanelle interspersed with chants, recitations and songs both Christian and Muslim, from the Byzantine, Maronite and Sufi traditions. The singers stood or sat on stage in a circle facing each other, rather than the audience, heightening the feeling of ritual. The concert opened with the Maronite Arabic Arsalah ‘llah, followed by Soerat Maryam, a sung recitation from the Koran, both celebrating Mary, as did many pieces in the programme. The first chants were sung by two soloists from behind the audience, as the ensemble on stage sung a rich deep throated drone. The constant return to solos over an underlying drone in between the polyphonic settings was inspired: the many chants and recitations were not only breathtakingly beautiful in themselves, sung with intense purity of sound and virtuosic ornamentation, but also enriched our experience of the polyphony immeasurably by throwing it into stark relief.

Hanelle’s polyphony arose out of a culture on Cyprus that mixed multiple influences, including French, Greek, Arabic and Turkish. His music comes from the Turin manuscript, one of the three principal sources for the Ars Subtilior, a French style of polyphony characterised by its refinement and rhythmic complexity. It was performed here with rich ornamentation from the singers, in somewhat the same style as the Greek and Arabic chants, including wonderfully liquid sliding elision between notes – the ensemble’s interpretation of debated aspects of the original medieval notation. These slides and glissandi gave an unsettling feeling to the music: a constant shifting of ground in which our sense of musical “home” was repeatedly displaced. The effect was hypnotic, deeply arresting: an almost microtonal polyphony in which Middle Eastern and European sonic norms melded into a living whole. It is next to impossible to pick out individual moments of beauty (of which there were many) – to do so is like trying to describe the individual turns of a labyrinth.

I was attracted to hear graindelavoix, whom I had never heard of before, not only by the repertoire, but also by the name. It is a reference to Roland Barthes, who talks about the “grain of the voice”, a perfectly turned expression of the unmediated heart of sound all singers seek, if they seek to make truthful art at all, and a notion that has haunted me in the years since I first read it. When listening to a concert such as this, the invidiousness of the critic’s or reviewer’s position becomes outrageously apparent. In this instance I am not well placed to offer any comment on issues such as the performance of music particular to one culture by members of another, or on whether performance practices that are unfamiliar to me were well represented. But most of all, how can a critic assess an act of shared humanity? Whatever technical or interpretative imperfections might be present from the performer’s point of view, how can a direct and passionate musical communication between human beings be anything less than perfect?

 I don’t know how traditional exponents of Sufi music, for example, would respond to, or gauge such a performance. I know only that I was racked with silent tears, my hand pressed in pain to my chest; that my emotions during the concert felt like ecstasy, my sleepless night afterwards full of inarticulate anguish, and the next day, when in a strange and grateful calm I began my daily practise, I found something entirely new in my own voice when I started to sing. There can be no rating, no mark out of five, appropriate for a sonic act which confers such a gift.