Once looked at equivocally, Rosalyn Tureck is now largely treated for what she is – a singular musician who never short-changed the composer whose cause she has assiduously espoused. Naturally, you may not always agree with Tureck’s views. They didn’t change radically in the 23 years that separate these recordings and the 1953 set of both books. But there are dissimilarities in application, and Tureck in 1976 is grander in communicating her ideas, her pianism more etched and commanding than of yore.

The First Prelude sets the tone, the opening declaimed imperiously over a sonorous C major pedal with a graphic drop to pianissimo in the fifth bar. It exemplifies her use of the instrument’s dynamic compass to expound Bach’s designs, which he mainly left to a musician’s discretion. Come the companion fugue, and a touch of grim determination creeps into an otherwise imposing pronouncement; it exemplifies another effect – an emphasis on contrapuntal entries that sometimes borders on didacticism, as in the Second and Fourth Fugues. She toes a harder line here.

Details also differ from the earlier set: in the Fifth Prelude the right-hand quavers in bars two and four of the first part, and their left-hand counterparts in the corresponding bars of the second, played as written in 1953, are given a dotted rhythm in the reading here. And the 13th Prelude is conceived on a much bigger scale, still largely ethereal but with a tighter grasp of structure and content that seems to expand the music into an even wider arch. Masterly, and that, all told, is indeed Tureck.

Sure, she can be intimidating; and if there are moments when you think that she is too insistent about what to listen for, then try the 1953 set, which is generally more complaisant, though in variable sound. There she mostly persuades rather than points out; the listener’s imagination is allowed a bigger role. Yet these 1976 performances, in consistently good sound, range further and are compulsively absorbing, perhaps in consolidation of earlier thoughts. You really need both interpretations. And since Tureck is now 89, she might not feel able to offer any more.