Hans Koch is the better known of these two Swiss reed players through his longstanding trio with drummer Fredy Studer and cellist Martin Schütz, and other projects, including Duets, Dithyrambisch (FMP) recorded with Evan Parker and Louis Sclavis. On that CD, Koch plays bass clarinet and soprano sax, as he does here with Denzler on tenor. Asymétries features four duets that probe the reeds’ margins in a confinding, often whispered exchange of secrets of embouchure, breath and attack. Long wheezing exhalations, rapid juddering, birdlike trills and chirrups, gaseous pops, purring and rasps have displaced the sounds of the centre ground. Dialogue occurs nonetheless as statements interlock and overlap, cryptic yet clearly and tightly shaped.