Kovacevich writes in his introduction to this new set that it was the Diabelli Variations – via the Serkin recording – that first made him love Beethoven. It’s a reading that still holds its head high today, and just a decade later, in 1968, Kovacevich set down his own recording, rightly acclaimed and something of a calling-card for the young pianist. But what of this new performance, made 40 years later? What is immediately striking is the sense of a cumulative whole, the tension and indeed speed with which he approaches the work. The work’s juxtapositions of the sublime and the ridiculous are presented with a vividness that sounds more live than studio-bound.

It’s easy to forget that the work was actually written in two distinct time-periods, the majority of it dating from 1819, with 10 more variations added in 1823, interspersed among the existing ones. It resulted in a work of a quite different – and more daring – shape from his initial thoughts. And unlike Bach, Mozart or Haydn, Beethoven doesn’t set up a particular style, tone or tempo that continues through an entire variation – instead there’s a sense of organic development through each number. Kovacevich emphasises this sense of continuous development with a certain fleetness of finger: his opening theme sets quite a pace (speedier than Brendel’s masterly live performance from 2001), and dances more lightly than many rival versions (though its exuberance matches Brendel’s in 1976). It’s certainly faster than his own earlier recording. But more important is the sense that Kovacevich has now encompassed the extremes of the work more fully. His understanding of Beethoven’s juxtapositions of beauty and crudity, reflection and action, and the sheer dynamic range, are fully exposed in this new version, which captures the piano sound beautifully. And not only in the later variations, as these juxtapositions become more blatant, but as early as Vars 3 and 4, the third almost trance-like, the fourth pushed hard towards the bar-lines to explosive effect, Kovacevich laying bare the extraordinary originality of his writing. That sense of being on the edge is a vital component of this reading. Occasionally you sense that he’s chosen a tempo almost too fast, that he’s a moment away from derailing (Var 23, for instance), but it never happens. Instead, it adds to the sense of “liveness” about this studio production.

Kovacevich has, in the intervening decades between his first and second Diabellis, recorded a complete sonata cycle and again that familiarity with Beethoven’s language in the final years shows, from the ease with which he presents the quasi-improvisation of Var 31 and his masterly handling of inevitable fugue of Var 33, to the discomfiting leaps and obtuse harmonies (Var 7), the extremes of range (Var 10), the creation of an illusion of speeding up through ever-smaller note values (Var 14) and that great Beethoven favourite – the trill – which plays an increasingly important part as the work progresses.

The humour, too, is there, but never overdone, whether in Beethoven’s earthy belligerence (Var 9), the tersely snatched ending of Var 19 or the blatant reference to Mozart’s Leporello in Var 22. But, again and again, Kovacevich reveals how that humour can tip over into something far more menacing: witness the rat-a-tat-tat of the left hand in Var 17 or the pathos as Beethoven at last switches to the minor in Var 29, finally putting the brakes on a seemingly unstoppable momentum, culminating in the fugue and its catastrophic collapse (Var 33). Perhaps in his younger days Beethoven would have ended the set with the fugue, but instead we get a final addition: a switch to C major and an utter change in mood, with a graceful, quasi-Mozartian idea, whirled ever higher. It’s as enigmatic and undefinable as anything Beethoven wrote and a transcendent ending to this remarkable performance.

Kovacevich might be less associated with Bach, but let’s not forget that his teacher was that consummate Bachian, Myra Hess. His approach to the Fourth Partita reminds me of another great Beethovenian: Richard Goode. In this respect he treads a middle path between the tonally slimline, rhythmically motivated readings of Angela Hewitt and the more obviously romantic ones of Cédric Tiberghien. And it’s an enlightening partner to the Diabelli Variations, not only in its basis in dance rhythms but also in its scope and its extrovert demeanour, whose tone is set with the grand Ouverture. Kovacevich brings an easy brilliance to the lightly tripping Courante and the bold contours of the final Gigue. Nor is he afraid to make Bach his own, drawing the listener in with his sotto voce Allemande, adding ornaments and playing around with rhythms, but all is done with the utmost musicality. Altogether, a disc to treasure.