You need your wits about you and the volume up to catch the head-motif opening Webern’s String Quartet of 1905, played by the DSQ and recorded by ECM at the prescribed ppp. A descending semitone and rising major third may not look much on paper but the theme has in common with the late music of Bach and Beethoven a strength and simplicity sometimes mistaken for severity. The pause markings over each phrase of the introduction are taken seriously; at 18 minutes, this is almost the longest performance on record (compare the LaSalle Quartet at just over 12 – DG, 11/71).

In this regard the DSQ are just surpassed by the Quatuor Diotima (Naïve, 6/16); that neither of these modern accounts hangs heavy is partly due to their broad palette of tone colours, tending in the case of the Danes towards a clean-limbed purity. More than either the Ardittis (Naïve, 12/91) or the Quartetto Italiano (Philips, 7/71, 4/88) – less idiomatically polar in this piece than you’d expect – the DSQ powerfully evoke the historical moment of the piece, poised as it is on the cusp of Webern’s incipient hero-worship of Schoenberg and adoption of his 12-note technique.

We might expect the DSQ above others to find an earthy vigour unmistakably prefiguring Nielsen in the cross-rhythms of the Scherzo of Beethoven’s Op 135. All the same, the 1826-ity of the quartet is respected in its playful opening exchanges, sounding more or less as though a single generation has passed since Haydn laid down his pen. All the pieces on this final instalment of the ‘Prism’ series stand on a threshold, and in this Op 135 Beethoven does so with the vitality and humour of the Diabelli Variations. The DSQ bring quiet radiance rather than sentimentality to the ‘deathbed chorale’ commonly appended to The Art of Fugue; the incomplete fugue unfolds in spacious legato lines, articulated as a string quartet rather than a keyboard transcription, in tune with the cool, Rothko-esque mood of secular devotion that infuses the series as a whole.