Music as sounding number occupied the minds of medieval music theorists and composers. Cassiodorus, the sixth-century Roman prefect and philosopher, outlined the concept in his influential Institutiones, a seminal text for medieval students of the arts. ‘The science of music’, he wrote, ‘is the discipline that deals with those numeric proportions that are found in sounds.’ The idea was still current a thousand years later, when Thomas Tallis created his setting of Spem in alium for a choir of forty voices. Sanctum est verum lumen is Gabriel Jackson’s ‘conscious homage to Tallis’s masterpiece’, a forty-part motet with numerical correspondences and coincidences that reinforce its links to Spem in alium. Sanctum est verum lumen, for example, occupies the same number of bars as Spem (a compositional coincidence), divides its choral forces into eight five-voice choirs (a deliberate formal strategy), and revisits many of the textural devices used by Tallis, from block chords and miniature chorales to shimmering imitative passages for upper voices and forty-part polyphony. Jackson has noted elsewhere that he wanted ‘to write a piece that was essentially about light; the text, though funereal in origin, is radiantly optimistic and invites a variety of ways of evoking that sense of light in music, from gentle luminosity to fiercely dazzling brightness’. The composer directs his multiplicity of light-seeking voices towards a central section, announced by chordal statements of the word ‘lucem’, in which the sense of regular rhythmic pulse is momentarily dissolved by a spate of overlapping choral fragments.

from notes by Andrew Stewart © 2013