Brown and battered like a tatty old cookbook, Masaaki Suzuki’s score of Bach’s St Matthew Passion lies open in front of me. On these pages, in the pencilled markings sprinkling each page, are the tiny adjustments of weight, balance and accent that make up one of the great musical recipes: what many have described as the perfect Bach sound. It has won him awards, critical praise of the kind usually reserved for the dead alone and a following that has snapped up every seat in Greyfriars Church, where he performs three Bach cantatas at the Edinburgh Festival next week with his Baroque specialist orchestra and choir, the Bach Collegium Japan.

“It is very hard for me to explain,” Suzuki says, stewing when I ask him to describe his sound world. He leans back in his chair and shifts his eyes to the heavens. “Most of the time what I find beautiful is a very pure, transparent, simple style: not too many embellishments, not too many ornaments, not too many wah, wah, WAHs.” — I don’t think he means trumpets — “This kind of pure, cutting-through, penetrating strength I love very much.

“It’s a little bit like the Japanese sword,” he says, locking his elbow, swishing his arm like a boy pretending to be he-man. The Japanese garden of neat shrubs growing from his head — a white moustache, goatee and silken fountain of flowing hair — begin to quiver with laughter.

He realises more and more that this Japanese concept of the “sword road” is at the heart of his conducting. “This sword road is not in order to kill somebody.” (I’d hoped not.) “It’s just to share this notion of the penetrating effect and to train yourself to accommodate this style,” he explains.

Suzuki, however, doesn’t wield his sword willy-nilly. Mostly, it remains safely within its scabbard. Besides, watching him in rehearsals at Aldeburgh with the young professionals of the Britten-Pears Orchestra, I get the feeling that this weapon is more of a butcher’s knife or surgeon’s scalpel. He stands before the orchestra, his sleeves rolled up high, his spreadsheet schedule before him, and, methodically, speedily and insistently — “this is really the last time” is a regular refrain — cuts and carves and whittles away at the sounds like a stonemason.

His sounds are always as pretty as a string of diamonds. The question is what pushes all this into mythical realms? What makes him one of the greats? One possible answer to this is faith. Suzuki is a Protestant, a member of one of the smallest denominations, the Protestant Reformed Church, of one of the smallest minorities in Japan. Despite his Church’s Calvinism (Bach was a Lutheran) it was in this world as a 12-year-old boy that he first discovered Bach, his chorales and the organ works, each Sunday service.

Faith, many believe, joins up Suzuki’s meticulous sonic gems and make them into a uniquely powerful whole. Protestantism might also go some way to explain the perplexing question of what a Japanese man is doing performing Bach in the first place, a match that many critics in the early 1990s, when he started up the Bach Collegium Japan, found suspiciously improbable. Suzuki’s first foreign tour, to Israel, had one sharp-tongued critic take aim: “ ‘What kind of relationship is possible between Bach and the Japanese?’ ” the reviewer began. Then he said he put on a CD and his jaw fell to the floor.” Many jaws followed, as Suzuki and his ensemble embarked on an epic Bach cantata cycle in 1995, in which, critically speaking, he blew all his Western competitors out of the water.

The key, Suzuki thinks, was not having a Christian tradition. It meant that the overwhelmingly non-Christian ensemble could proceed without historical preconceptions and, as they were by and large all starting from theological scratch, could fashion something completely fresh. “Sometimes to record one short chorale it took two hours to explain what the text meant and to talk about vision and intonation, etc,” he explains.

Such an approach could be nerdy if it wasn’t for Suzuki’s childlike enthusiasm for the work. Even his barely intelligible ramble through the abstract-number symbolism of the St Matthew Passion is filled with such enthusiasm that I almost feel I know what’s going on.

Bach’s codified world of inner mysteries is a world away from the showiness of Handel. But this is what Suzuki will be tackling less than 24 hours earlier at Usher Hall in the first of his two Edinburgh concerts when he conducts the Collegium Japan in a concert performance of Rinaldo. Has he done Handel before?

“I haven’t done Rinaldo before, but I have done Giulio Cesare and some Monteverdi,” he says. “Handel’s operas are of course very interesting,” he pauses. “Well, maybe not all of them.” Rinaldo is luckily one of his favourites. And he’s grateful to get a chance to explore other repertoire. “I find it a little difficult that everybody asks me to do Bach,” he laments, “when sometimes I want to do something different: Mozart, Beethoven or Mendelssohn.”

He loves exploring other territories. The colourful and theatrical effects of Handel, in the orchestration and choral writing, is a special joy for him. “But,” he adds, “Bach is my home. And coming home is a very nice feeling for me.”

Suzuki’s performance of Rinaldo is on Monday at 7pm in Usher Hall, Edinburgh; the Bach Cantatas concert is on Tuesday, 5.45pm, at Greyfriars Church, Edinburgh (www.eif.co.uk)

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