Trevor Pinnock arrives at the appointed hour in a café on Marylebone Lane ready to discuss his new recording on Linn of Mozart’s Serenade No 10 in B flat, the Gran Partita, K361 – with the Royal Academy of Music Soloists Ensemble – clutching two scores: a photocopy of Mozart’s autograph score alongside his well-thumbed modern edition. I’ve brought along the 2005 Urtext edition, which means that, between us, we’ve unwittingly upgraded this section of the magazine to ‘Musician and the Scores’.

It’s nearly a year since Pinnock finished his recording, but the fantasy world of Mozart’s most ambitious, longest and most technically complex wind serenade is still alive and kicking inside his brain – ‘It thrills me just to look at that on the page!’ he beams at one point. But before digging inside the notes, Pinnock wants to make something clear. Although Mozart’s composition does indeed slot into the 18th-century tradition of Harmoniemusik – music for wind ensemble often performed in the homes of those well-heeled enough to commission it – the Gran Partita is more than just entertainment. ‘There are elements of this music that run much deeper,’ he asserts.

Much about the Gran Partita – the precise date of its composition, and how Mozart intended the ordering of movements to function – remains shadowy, but beyond doubt is that Mozart wilfully exploded polite conventions surrounding Harmoniemusik, delivering seven substantial movements conceived for a vastly enlarged ensemble. ‘The dating is uncertain,’ Pinnock says, ‘but we know it was written after Idomeneo, which itself is a real high point in the way Mozart deals with the Harmonie. And here he gives us an expanded ensemble – not only two oboes, but pairs of clarinets and basset-horns with four French horns instead of the usual two. The combination of basset-horns with the horns makes a tremendously rich and dense sound, immediately apparent from the sonority of the opening chord. Having the four horns, in F and in B flat, hands Mozart a nice variety of notes, while the basset-horns put a lot of pudding in the middle.’

Given Mozart’s structural largesse – his sonata-form first movement occupies symphonic dimensions and leads to two slow movements interspersed between two minuets, climaxing in an elaborate set of variations and a tub-thumping finale – I wondered what Mozart did to unify his structure. Are there melodic and harmonic threads embedded inside the first movement that are developed subsequently? ‘I think that might be going too far,’ Pinnock responds, ‘but certainly Mozart strikes a fine balance between the sequence of dances and his reflective movements. It is questionable, though, how much he thought of it as a unified whole, and we need to be careful about imposing our later preconceptions on to earlier times.’ Perhaps Mozart viewed it as a proto-jukebox, a selection of tracks to be picked over as required? ‘I’m not saying it’s not that – but the truth is we simply don’t know. But it must not sound like a sequence of bits if we choose to perform it as a whole. The balance of speeds and atmosphere, and how one piece moves into the next, becomes of prime importance.’

‘My modern edition is scrupulous and well done,’ Pinnock explains as I ask what consulting an autograph score contributes to piecing together an interpretation, ‘but autograph scores always do give me little ideas. For instance, at the beginning of the first Minuet, Mozart, in the first oboe part in the autograph, begins the slur on the first minim and it reaches right through into the next bar, while in the other instruments the slur starts only on the third-beat semiquavers. Perhaps we could say he’s made a mistake; after all, he writes very fast, and it’s true the slur doesn’t appear the next time around. But actually we have a clue about the sort of length Mozart expected his first note to be played. It was customary during this era to shorten longer notes, but that he slurs the leading part tells me that the oboist is going to play a long note at the beginning.’

He points to a comparable example in the Romance where, in bar 20, editorial slurs differ from Mozart’s hand, and when we flip back to the work’s beginning, an intriguing line of enquiry opens up around how to articulate Mozart’s opening rhythm: crotchet, dotted quaver/semiquaver, crotchet. ‘Some people do really quite sharp double-dotting here,’ Pinnock explains, ‘but personally I don’t like the sound. Later [in bar 12] he writes very precise double-dots and, again, we have to decide what that implies – but playing dotted notes with machine precision is likely to lead to rhythmic stiffness.’

But, I probe, why might some performers choose to double-dot the opening semiquaver when Mozart, only a few bars later, notates actual double-dots? ‘There are all sorts of arguments,’ Pinnock suggests, ‘and if you were trying to justify double-dotting in the first bar you might say Mozart wrote it differently in bar 12 simply as a notational device: he wants the oboe to play with the basset-horns and that was the clearest way to write it. You could argue that if you wanted to – but I don’t want to. I considered double-dotting the opening, of course, but the music told me otherwise.’

Pinnock describes the process of bonding with composers via making imaginary phone calls, and pressing questions surrounding Mozart’s bass-line made him reach for speed dial. ‘The bass-line was played originally on string bass,’ he explains, ‘because period contrabassoons could not have given him sufficient flexibility. But if we’re agreed that playing this music on modern instruments is justifiable, then the question of what instruments becomes one of informed musical decision. When I heard the marvellous playing of the bassoonist [Alice Quayle] producing almost a bowed effect, I knew that using a contrabassoon was right. And so I phone Mozart – by which really I mean I use my musical conscience – and I feel he’d be delighted with the sound we have on the record.’

We close by discussing Mozart’s intricate chain of variations, and how to integrate so many characterful individual moving parts into a convincing whole. ‘I like that, in your edition,’ Pinnock enthuses, ‘the editor has left out the suggested Andante in my score; there’s a particular elegance to this theme and why impinge upon that with a generalised tempo mark? With a theme and variations you need to be aware of your starting point and, on the journey, follow your fantasy. You see how wonderfully Mozart has used the characters of different instruments throughout the variations? That miraculous moment in Var 5 when he has basset-horns and clarinets play in rapid demi-semiquavers surprises us, even now, and trying to imagine how people might have been amazed in the period by, say, Mozart’s modulations or orchestration is crucial. Our ears have been spoilt by too much music – but as musicians we need to point to such remarkable moments and express, though not in an artificial way, that they are very special and that you need to listen.’

Gran Partita – the historical view

Johann Friedrich Schink – Litterarische Fragmente, 1785, in response to a partial performance of the Gran Partita

‘I heard music for wind instruments today by Herr Mozart, in four movements, glorious and sublime. It consisted of 13 instruments…Oh what an effect it made – glorious and grand, excellent and sublime.’

Peter Shaffer – Salieri in the play Amadeus (1979)

‘On the page it looked nothing…Just a pulse – bassoons and basset-horns – like a rusty squeezebox. Then suddenly – high above it – an oboe, a single note, hanging there unwavering, till a clarinet took over and sweetened it into a phrase of such delight!’

Pierre Boulez – Interview, Gramophone, December 2008

‘The big Adagio is…a moment of genius. You have this introduction that is very slow with just a chord, an arpeggio…But it’s so wonderful, so mysterious that it has you thinking “What will happen?” It’s a magical, ceremonial moment – like a ritual.’

Pinnock's new recording of the Gran Partita Serenade is out now on Linn Records. For more information, visit: linnrecords.com

This article originally appeared in the May 2016 issue of Gramophone magazine. To find out more about our various subscription offers, visit: magsubscriptions.com