Nielsen for piano four hands. Who knew? Probably only those who had been assiduous enough to read the prefaces to the modern Complete Edition, or anyone who had read through the vocal score to Saul and David.

The opera contains two orchestral sections that Nielsen himself arranged for piano duet: the Prelude to Act 4 and the subsequent Battle Music. Both are remarkably effective as heard here on two pianos rather than one (an entirely reasonable choice, so that textures aren’t cluttered and can even be amplified), and in performances that vividly capture the music’s irresistible drive.

But the main event is the Sinfonia espansiva. Convinced that he had composed a symphony that could give him a breakthrough in Germany and elsewhere, Nielsen produced a duet version that he and/or his friends could demonstrate to conductors, which they did with some success (who knows how his international reputation might have taken off had the Great War not intervened). It seems that the only surviving copy is a manuscript in Copenhagen’s Royal Library, which Kristoffer Hyldig took the initiative of digging out and transcribing.

Hyldig and Sandberg take the ‘expansive’ first movement at full tilt, and the result is thrilling. Apart from achieving optimum clarity and synchronisation, they have a sure instinct for locating the pillars and arcs of the structure. They broaden fractionally as if to accommodate the refulgence of Nielsen’s orchestral tuttis, and they bring just the right amount of interiority and affection to lyrical contrasts. Understandably, they don’t try to work in the slow movement’s vocalise solos, but Nielsen’s entranced pandiatonic coda still registers movingly. Just as lovingly shaped are the exploratory, testing-out character of the third movement and the celebratory affirmations of the finale. At the opening of the latter, the octave doubling of the theme is perhaps less persuasive, but there I may be picking a quarrel with Nielsen himself.

The choice of a Steinway for the upper parts and a Fazioli for the lower ones may be counterintuitive but works fine in practice. Occasionally themes in the mid range don’t quite come through as one might hope, but otherwise the textures are 100 per cent convincing, helped by well-ventilated recording quality.

A delightful, unexpected bonus is the Johann Strauss-like Højby Rifle Club March, composed by Nielsen’s father and only rediscovered in Nielsen’s own arrangements in 2023. Engaging and authoritative booklet notes help to make this an exceptionally rewarding disc.