One of the leading virtues of this performance is the way each player colours and characterises individual voices. A good place to sample is the Seventh Contrapunctus, where Bach ‘juggles [the theme] in three different tempos’ (to quote Paul Epstein’s exhaustive analysis), a nightmare to get right, I would imagine: and yet because the blending lines remain distinct, they are projected with total clarity. A secure sense of pulse also helps.

Interesting that the Emerson’s Lawrence Dutton borrowed a 1986 tenor viola from the Juilliard Quartet’s violist Samuel Rhodes. I am assuming that this is the same instrument that Rhodes used for the Juilliards’ own Art of Fugue (Sony), its range extended downward by a fourth. Comparing the two recordings in that seventh fugue finds the Juilliards favouring a quicker tempo and more forceful attack whereas the straighter-laced Emersons rely more on contrasts in tone.

Another novelty on this new release concerns instrumental positioning: in order to highlight acoustical differences between the straight and inverted fugues of Contrapuncti Nos 12 and 13, the Emersons reverse their seating for the inverted versions. Here, as at other key points in the score, a forthright playing style helps focus the sublime ingenuity of the writing. Duets work well, the Canon of No 16 shared between Dutton and violinist Eugene Drucker (almost twice the speed of the Juilliards this time), the Canon of No 17, between cellist David Finckel and violinist Philip Setzer. The unfinished quadruple fugue (14) is played with formidable concentration: it stops where Bach laid down his pen, mid-phrase and without ceremony (the broader-paced Juilliards take a similar stand) though I find myself gravitating more to the mellifluous but virtually vibrato-free Keller Quartet in ECM, where dialoguing is especially keen. The Kellers leave us on that last unresolved cadence, whereas both the Juilliards and the Emersons add a compensating chorale, Vor deinen Thron tret ich hiermit, dictated by Bach from his deathbed. Not certain myself whether it works in sequence, but you can always programme it out. The generally excellent Delmé Quartet (ed. Robert Simpson) use Tovey’s brave but speculative completion.

Having revisited the Emersons three or four times, I still admire their Classical exegesis, the liveliness and urgency of their phrasing and the warm glow of their tone. Theirs is an eminently satisfying performance. Of available modern-instrument rivals the Kellers achieve the most ethereal effect and I retain a fondness for the consistently alert Juilliards. But the Emersons’ intensity reminds us where the music is going and who would later take a lead from late Bach, Shostakovich and Bartók for example. These historical connections are vitally important.