Should it always be a viola da gamba of six or seven gut and metal wound strings, tuned in fourths – a third in the middle – played with bow held underhand, neck wrapped in adjustable frets, no end-pin? Or a Baroque cello of four gut strings tuned in fifths, played with convex bow conventionally held, unfretted neck, no end-pin? Perhaps a difference in timbre between the two instruments might then have not been conspicuous; but here there’s a brighter than expected edge to Tatty Theo’s tone. Has she substituted metal strings?

Whatever, there is a close match between cello and a harpsichord of cutting transients which fits the businesslike virtuosity of much of the playing. Choice of tempi cannot be faulted and rhythm is exact; too often very exact, especially for the kernel of slow movements to be revealed. Johann Mattheson, a contemporary of Bach, speaks of ‘the tenderness of adagios’ while believing that ‘a highly articulated style, especially in lyrical pieces, has little or no flowing quality and is to be avoided’. Absence of pliability from Theo and Carolyn Gibley, not only in the slow movements but in the fast ones too, is a flaw that devalues their performances of Bach père et fils. A difference rests in the interpretations of Jordi Savall (viola da gamba) and Ton Koopman, for whom the absence of dynamic and expressive markings is not a restriction but a spur to uncovering the dramatic shapes of these sonatas through their varying moods.