Bach’s glittering reputation as a virtuoso organist was based primarily on his extraordinary abilities as an improviser, echoes of which we can hear in the Passacaglia in C minor: its 20 virtuoso variations over a repeating bass carefully overlap one with another and lead ultimately to an imposing double fugue that brings a satisfying textural and harmonic catharsis.

BWV549 and 561 both follow the prelude–fugue–postlude form. In BWV549 the centre of gravity lies in the fugue, whose delightfully quirky subject is treated with an almost reckless playfulness. In BWV561 it is the postlude that captures the imagination: the composer (possibly not Bach) waits until then to introduce the pedals, above which he develops brilliantly figuration. The coda of the Fugue in C minor BWV574 is even more striking, and has the rhetorical drama of a semiimprovised toccata.

The chorales BWV639–41 are taken from the Orgel-Büchlein (‘Little organ book’), which collects 46 chorale arrangements Bach wrote while he was organist at the court of Weimar in 1708–17. Herzlich tut mich verlangen, the so-called Passion Chorale, is harmonised no fewer than four times, each time differently, in the St Matthew Passion; here Bach treats it to delicate melodic embellishment.

Played on the Organ by Gerhard Hradetzky 1995, Meolo (Venice, Italy).