You need only whisper into the microphone, says Andreas Scholl, as he twiddles the dials on his Yamaha digital mixing console. "It makes it easier to sing." We're in Scholl's private recording studio, in the same building as his modest Basle apartment, but the sound wafting from the speakers is nothing like a whisper. Scholl's face breaks into a disarming smile as his latest pop song picks up momentum, wrapped in a cushion of symphonic strings and faux-baroque trumpet flourishes. Entitled "All beauty must die", it is part of an album of easy-listening ballads he has written and recorded, with orchestral arrangements by a German friend.

Scholl's enthusiasm for his pop songs is as catchy as the beat that carries them along. A laidback personality with a towering frame and a touch of innocence about him, he has performed them in his native Germany and had them broadcast. But the star counter-tenor has yet to sell the album to his record company. When Decca poached Scholl from Harmonia Mundi in the late 1990s, it reluctantly agreed to release a pop album, but the delay in doing so suggests that few at Decca see it as exportable.

Instead, Decca has been exploiting Scholl's supremacy in the core counter-tenor repertoire, from Dowland to Bach. That's where he made his name, it's the music people expect him to sing, and it sells - in Scholl's case, tens of thousands of CDs. And the more you listen to his new recording of Handel's Saul, the more there is to admire, especially on those long notes where the steadiness and beauty of his voice really tell.

Scholl had no trouble selling Decca the idea for his other new CD, a collection of cantatas by late 17th-century composers associated with the Arcadian Academy of Rome. Arcadia is on a level with Cecilia Bartoli's Salieri album: obscure, previously unrecorded repertoire championed by a celebrity singer. And like Bartoli, Scholl is promoting Arcadia on a recital tour, starting this week in London and Munich.

Selling Arcadia to the music-loving public presents singer and record company with a tougher task than Scholl's previous solo albums: the music lacks the limpidity or expressive depth of the folk songs, heroic arias and sacred music on which he has hitherto staked his reputation. They're a bit of a souffle.

Arcadia was nevertheless Scholl's idea. What appealed to him in the first instance was not so much the Arcadian composers' music, about which he knew little, but the semi-secret nature of their society. It formed a link with his fascination for the Knights Templar, for Poussin's enigmatic painting Et in Arcadia ego, for the world of secret rites and coded messages. Having looked up the composers' names in the New Grove Dictionary of Music, he handed a list to Decca with the suggestion that it could make a CD programme.

Decca commissioned Italian musicologist Alessandro Borin to be what Scholl calls "a sort of Indiana Jones - going to libraries, pulling out dusty scores and autographs, making a selection based on his knowledge of my voice, and creating a performing edition. Four months later, I had a pack of beautiful computer-printed music."

And has he divined a secret code? Scholl gives nothing away, merely observing that the printed notes are a code, the unlocking of which is an interpreter's challenge. "The black dots within the five lines (of the stave) don't represent the creativity of Handel or Scarlatti, it's not the complete truth. There's a strong improvisational element in baroque music which we have lost, and it also finds itself in baroque teaching: there were no fixed rules. It was more a question of imitating the teacher, and then, after a while, emancipating yourself from what the teacher did.

"I remember Rene Jacobs telling me 'try this, try that, but remember, you're the one who will be singing it in concert'. You have to be convincing, you can't blame it on your teacher. If it's elegant but boring, you can't say 'I'm sorry, dear audience, it's bor ing but it's what the composer wrote.' I don't put synthesisers into the Arcadian cantatas, I don't use Mozart's ornaments, but I have the background and I try to stay in a style. In the end, I take responsibility."

Scholl admits that his whirlwind success as a recitalist has limited his exposure in opera. Since his stage debut in Glyndebourne's Rodelinda in 1998, he has done just one other role - the title part in Giulio Cesare in Copenhagen, which he will reprise for his Metropolitan Opera debut in 2006. A brilliant linguist, he is preparing a poetry-and-song evening with the director Mark Lamos, but feels let down over other projects, such as Glyndebourne's Giulio Cesare next year, which he had been led to believe were his.

"Music is a very emotional thing - it's as if all your colleagues turn into your friends. But the culture of the music industry at a certain level is insincerity. On the surface everyone is friendly, but underneath it's a business. If there has to be a decision, don't count on friendship any more. I don't want to be cynical. I'm just disappointed."

With a four-year old daughter in Brussels (where his ex-wife lives) and a new non-musical girlfriend from Romania, Scholl, 36, takes an unhurried view of life. He knows and admires David Daniels ("there's room for us both, we're so different in what we do"), wants to continue singing till he is 60, and says his motivation for signing up with Decca was "to reach a big audience and develop projects I couldn't otherwise do. In the end, it's not about the money."

Scholl also admits to being religious. "Why do I sing? I have to think a lot about that. The concert is a ritual, it's there to trans-mutate the human spirit. It's the idea that the composition, the art, is an expression of the creativity of a composer, and the creativity is a gift of God, it's our divine spark. It goes back to the punishment of Adam and Eve in the Garden of Eden, which is a very questionable story. They wanted to eat from the fruit of knowledge, but God says no, get out of the garden, you will be so busy earning your daily bread that there will be no time for you to think about who you are.

"Creativity is the work of Lucifer-light-bringers, it's people who say 'hey! - this is something I give to you, and we can perform it,' and a basic thing happens that can also happen in a pop concert: people arrive tense and stressed, and the music relaxes them. When they leave, they're changed, and the interaction with whomever they meet is changed. One could consider the concert as a cell, a constant impulse to change the collective state of mind. It sounds big, but that is how I see it." The 'Arcadia' tour begins at the Barbican, London, tomorrow. Tel 0845 120 7550. Then on to Munich, Cologne, Metz, Paris, Bordeaux and Lyons.