It is a muggy morning in a quiet south-western suburb of Berlin. The evening before I had sat outside to eat on an August night of cut-glass stillness and clarity, but rain has crept in during the small hours to blunt the air, and even though it has stopped now its heavy residue of moisture is everywhere. Members of the Akademie für Alte Musik Berlin and the RIAS Kammerchor arrive on foot or bicycle at the former dance hall that is the Teldex studio, most of them dressed in shorts and sandals. Together they gossip quietly, smoke or warm up. For a group that is about to spend a week recording one of the great monuments of Western art, they seem remarkably relaxed. But then this is their home town, and after several days of rehearsal and balance tests, perhaps for them it is a bit like turning up at the office. Only producer Martin Sauer looks busy, making sure everything is in place and attending to small, final adjustments. Then, almost at the last minute the conductor arrives. In what seems like a moment everybody is in place, everyone focused. René Jacobs has his blue conducting pencil in hand and Sauer’s voice is readying everyone over the talkback. We are about to start on Bach’s St Matthew Passion.

Straight away we are at the heart of the action. This first morning is to be spent on crowd scenes, and it is soon apparent that this is to be a performance of some theatricality. Evangelist Werner Güra is making expansive arm gestures and arching forwards – not what you would normally see in a concert! – and in the scene where the crowd spits insults at Christ there are taut, angry chords from the cello and basses and aggressive faces in the choir. Sauer’s voice is on the talkback in a mixture of English and German, politely probing for clearer words and more flexibility in the declamation. ‘Could the Evangelist make more of a differentiation between narrative and reported speech?’; ‘Make more of an emphasis on “Laß ihn Kreu-zigen!”’; ‘Why is “getan” so slow?’ There is much concern to tighten up cadences, and the great choral shouts of ‘Barrabam!’ require several takes, interleaved with rehearsals and discussions about how long to hold on to the organ chords.

The musicians work with pace and calm concentration. Sauer, kicking off his shoes in the control room after a foray on to the studio floor, declares that ‘it’s nice to be able to take time over things, and not just to be doing two takes and then, if everything is together, move on’. But even so, the carefully drawn-up recording schedule has to be adhered to. He smiles and ghost-conducts when he likes what he is hearing, but if a take keeps failing in the same bar he drums his feet under the desk in frustration (well out of sight of the musicians!). When lunchtime comes, however, he is a happy man. They are two chorales ahead, and there was even time to go back and improve ‘Laß ihn Kreuzigen!’.

Amidst all this Jacobs has been a calm presence. He never raises his voice, and offers quiet, singerly advice to the soloists standing near him. He himself sang in the St Matthew Passion as a treble at Ghent Cathedral and later recorded it as a countertenor with Herreweghe and Leonhardt, but this is his first recording in charge, and as usual he has come up with a new approach to it. In this case it derives from musicologist Konrad Küster’s suggestion that at the original performances in St Thomas’s Leipzig of this great piece for double orchestra and choir, the music for Choir II was originally performed from the small, so-called ‘swallow’s nest gallery’, high up above the crossing (it was dismantled in 1740), and that the congregation would thus have perceived the two ensembles in an asymmetrical ‘near-and-far’, ‘big-and-small’ relationship rather than the equal left-and-right we have become used to. And indeed the studio has been carefully laid out to capture this effect, with Choir I and its orchestra up at the front and a smaller Choir II set back to give a more distant sound. ‘We had them at the furthest distance we could get in the studio,’ Jacobs says. ‘We weren’t sure it would work at first but there were no ensemble problems – at least, not more than in the normal set-up!’

It sounds daring, but Jacobs is convinced it works. ‘It’s funny, I read Küster’s article and found it interesting because I always had the idea that it could have been done that way, without having any knowledge of a musicological basis for it!’ He also points out that it is more than just a logistical experiment: ‘The words for Choir I and its soloists are all concerned with the action – Jesus and all the other characters except the two witnesses are in it; the words for Choir II are for onlookers trying to influence or stop the action. We imagine the listener sitting in the church near to Choir I and hearing Choir II coming from afar. It makes an especially big impression in the numbers that are dialogues between them.’

The afternoon session is devoted to getting down just three numbers. The soprano II aria ‘Blute nur’ is sung by Christina Roterberg, a boyish-toned soprano from the choir whose freshness and heart seems to draw an extra spring from the orchestra. When she has finished, her colleagues in the choir congratulate her warmly. The soloist in the dialogue recitative and aria for Tenor I and Choir II ‘O Schmerz! … Ich will bei meinem Jesu wachen’ is Topi Lehtipuu, and, in the course of recording these vocally demanding pieces, he receives some impromptu German coaching and the odd bit of firm interpretative instruction. ‘There’s no negotiation on that?’ he enquires of one of the conductor’s request. ‘No, it’s black and white!’ comes the answer. The choir works patiently at the repeated takes, perhaps like me enjoying the chance to notice anew just how subtle Bach’s soothing choral interjections are here. At last, when everything in the aria is covered, Sauer suggests one final take. ‘The whole bloody thing?’ asks a surprised Jacobs.

‘Thank you, that was worth doing,’ says Sauer after the take has finished and he is able to call a halt to the day. The doors open on to the humid grey evening, and the musicians disappear until tomorrow.

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Bach's St Matthew Passion will be released on October 14, 2013, and will be reviewed in the November issue of Gramophone, on sale November 11