Look at what Bach said: ‘Six sonatas for obbligato harpsichord and solo violin with a bass accompanied by a viola da gamba if you like’. They are, in fact, trio sonatas with the middle and low voices played by the harpsichordist. Andrew Manze and Richard Egarr like the gamba for Nos 1 and 2 only; James Ehnes/Luc Beauséjour and Rachel Podger/Trevor Pinnock, not at all.

Egarr and Pinnock’s recordings give the keyboard its due, and the instrumental perspective reflects Bach’s priorities. Beauséjour’s slender-toned harpsichord, however, doesn’t offer enough sonority for the low voice to speak as authoritatively as it does with Pinnock, in whose performances the absence of a reinforcing gamba is not felt. But he can be a touch square which Beauséjour is not, except in the opening Adagio of No 3.

In his book Authenticity in Performance (CUP: 1990), Peter le Huray – basing his thesis on the writings of Diruta, Mattheson, Quantz and Bach’s cousin Walther – says, ‘We are so accustomed to thinking of rhythmic give and take as a characteristic of romantic music that the idea of a kind of rubato in baroque music may come as something of a surprise’. And rubato, together with Quantz’s belief in the importance of line-shaping, is evident in the approaches of Ehnes/Beauséjour. Sometimes, as in the first movement of No 2, Ehnes produces too lush a sound; but he is not short of variety in his articulation and phrasing, even veering towards severity in the second movement of No 4.

The other artists are equally aware of expressive requirements, and the differences between the three pairs lie in how they weight the various facets of these remarkable works. You really ought to have all the interpretations; and they are sensitively recorded though Podger/Pinnock may need a cutback in volume.