Ictus is Belgium’s leading contemporary music group. Famed for their incisive interpretations of Fausto Romitelli and Georges Aperghis, the group likes to present concerts with commentary, offering on-the-spot clarification of music which often goes unexplained. Ictus recently joined Michaël Levinas – theorist, composer, and performer (with his ensemble, l’Itinéraire) of spectral music – for a revealing lecture-demonstration based around the latter’s String Quartet No. 2. Two performances of the work were separated by a lengthy interview with Levinas exploring the compositional technique in the work. The interview was conducted by Jean-Luc Plouvier, pianist and artistic co-ordinator of Ictus.

Written in 2005, the quartet makes use of an expressive microtonal canvas of shifting glissades and spiralling echoes. The music recalls Giacinto Scelsi in its purposive rigour and Gloria Coates in its emotional intensity. The performance was strong; the crying motifs of the first movement’s violins wounded each broken iteration of the climbing ground bass in the cello. The second movement was burnished and brimming with tension; phased and irregular rising figures spread across the ensemble, fracturing across registers and times and crowned by the vivid tone-colours of the ensemble.

After the music drew into silence with the down-tuning of the cello’s C string and it’s spectrum evaporating, Levinas – blithe but cheerful – climbed onto the platform for his interview. The first fifteen minutes were broad, covering the composer’s biography and his associations with other spectral figures such as Gérard Grisey. The physical abstraction at the base of the style, the acoustic theory which frames so much spectral inspiration, was contrasted with the expressive immediacy of the music.

Spectral music is often perceived to be complex music. Levinas refuted the notion by showing the simplicity of his work’s construction, laying out unreservedly the compositional technique used in his quartet. With ample illustration on the piano, from the four players who were each in turn asked to partake, and from recorded examples taken from his back catalogue, Levinas showed how he builds music out of a simple apparatus of gestures and forms, namely: canon, sequence, phasing, glissandi, pedal points and ‘broken’ (brisée in the French) times and scales. The latter give the music an appearance of sonic illusion that is similar in its uncanny affect to the Shepard scale, which was also played, by way of comparison. The surfaces of the music slide in and out in an ungraspable flow of tone and timbre, pulling the listener into an auditory snakes and ladders.

The plain building blocks of Levinas’ technique are mediated by one micro-division of an octave, thus creating the spectrum of the work and giving rise to the elision and mystery that is fundamental to the auditory hallucinations of spectral music. The musicians’ second performance of the work, which followed the interview, shone with a clarity unavailable earlier, and yet the glistening obscurity of the sound was undiminished. If anything this second reading was even more impassioned and perplexing than the first; the emotional climax of the music was more immersive, more oceanic. Explanation thus penetrates procedure, but not poetry. Spectral music, at least Levinas’ spectral music, came out of the evening revealed, yet still strangely ravishing.