Ten experts decide who and what changed the course of music history.

Late in the 14th century, a small coterie of renegades began a decades-long fascination with the experimental. Beginning in Avignon and spreading to northern Spain and on to Cyprus, a handful of radical thinkers took rhythmic and melodic complexity far beyond what had hitherto been known, challenging and stretching the limits of musical notation, performance and reception. They were joyfully, willfully, working in unfashionable terrain, marvellously out of step with their time.

History has often written of them as ‘mannerists’, indulgent and excessive, lost in their notational strangeness and creative extravagance. The movement was dubbed Ars subtilior and its legacy – found in Chantilly Codex, Modena Codex and the Torino Manuscript – remains a source of fascination. The music of Baude Cordier, Jacob Senleches, Johannes Ciconia, Solage and co. has never been widely popular. It’s exquisite, both sonically and imaginatively.

These ‘cerebral’ composers had ears shockingly well attuned to the sounding qualities of music. They were trying to notate with a relationship to sound that combines both mathematical and sensual laws. Trying to find a notation to even begin to do justice to the malleability of time when...