For almost 20 years, Manfred Eicher's ECM has been an island. Contemplation, clarity, distance, the quiet intensity; "the most beautiful sound next to silence". ECM has had its moments of commercial calculation but, as Eicher says, "you can't calculate with music" – at least, not the way he hears it.

The rigorous principles which Eicher has held over his recordings have created a body of music that seems purposely designed to reject most of the cant and modishness attached to the contemporary outpourings of the world's record companies. It is not easy terrain. ECM's exterior can be forbidding, from the austerity of the record sleeves to the almost doctrinal musical paths which the label's favourite sons have followed. Even more than Blue Note or Candid or ESP or any of the great jazz labels of the past, ECM has established an identity which cloaks its content as strongly as its artists do.

Manfred Eicher doesn't see it quite that way, of course. To hear Eicher speak, one would think that the whole enterprise has been directed on laissez-faire lines. Eicher started by borrowing some money and recording albums by then-starless names such as Keith Jarrett, Jan Garbarek and Chick Corea. It could have amounted to no more than another eager little European independent, but something about those early releases clicked. Instead of conveying the hot enthusiasm which a label like BYG had approximated with their series of expatriate Black American albums, Eicher's records were cool, considered, luxuriantly recorded.

With hindsight, ECM has looked to be a superb piece of marketing ever since. In the early 70s, the label forged a clear, boundary-crossing identity when jazz was confused and homeless, continued to set exacting standards of recording as digital conditions took over the industry, pre-empted the widespread return to acoustic music in the last decade or so, fostered "world music" collaborations before the term had been coined, elevated even the lesser musings of its artists by its presentation and thus maintained a sense of creative continuity, anticipated the demands for quality and personal kudos by an older record buying audience, and promoted the concert-hall ambitions of players such as Lester Bowie.

Eicher sees none of this as part of ECM's philosophy. His intention, he says, is simply "to capture what is going on in the music". He has said elsewhere that "by withdrawing, we are much more likely to achieve clarity than by always being in the middle of things". It's not so much that ECM is intellectually lofty or pretentious but simply remote from the voracious concerns of an industry bent on selling. Even small independents appear tigerish about their product compared with the distracted demeanour of ECM.

It's easy to be sceptical of Eicher's philosophy and intentions, which is why so many critics have been, for as long as the label has gone on. One can forgive the producer for seeming bitter about it all. He's shored up 20 years of people saying that he suffocates musicians and stifles passion, that ECM is cold, soulless, pompous, unemotional, dry, dull. His response has been to withdraw advertising and refuse interviews and carry on with his work.

When he came to London last spring, to work on the recording of Arvo Pärt's Passio, recently released in ECM's New Series of albums of contemporary composition, Manfred Eicher took out a morning to walk down to a Hampstead coffee shop and talk about his label. He is a slim, rather careworn-looking man, whose great energy and dedication don't always break through a cautious temperament. His small, shapeless face is surmounted by a careless thatch of greying hair, his eyes have the pale glitter of graphite; he's not much given to laughing. But he warms to anything he senses is kindred to his own beliefs.

It's tempting to think that ECM's New Series, a matter close to Eicher's heart, will be the main thrust of his future operations. He talks of Arvo Pärt with the same primary concern that might once have been directed to Eberhard Weber or Keith Jarrett. But he denies that he places more importance on anyone part of ECM's repertoire, and it's more likely that he's narrowing his interests to certain qualities in the music, whatever the genre. It's not as if ECM has changed very much over the past 20 years.

"Since I've been doing it for 20 years I'm much more involved and I don't see it from the outside. I do feel that our premises are still the same, but I hope it has changed in 20 years. I think there are enormous changes, actually."

Such as?

"Like in the New Series. In the differentiation of sound in the different projects that we're doing. That kind of stupid criticism that one reads now about the so-called ECM sound is so irrelevant that it's as irrelevant as comparing Pat Metheny's records now with what he did when he was making his group records with us."

There's no need to open this old wound in Eicher's hearing: he's only too ready to do it himself. But recording the sort of music ECM has enshrined has changed throughout the industry. The elegance and resonance of a typical ECM mix has been achieved in many fields; even conventional standards of recording, on one-day-in-the-studio jazz records, have a finesse unimagined 20 years ago.

"It's improved enormously, and yet, OK, that's a given thing, I'm glad that things have improved. But if you look to classical music or the fine Decca label or L'Oiseau Lyre in the past history of recording, they were always good. In jazz, people weren't used to it, and people talk too much about sound. For me, it's only the technical side. The musical side is much more interesting.

"Every kind of music you're going to record requires its special sound. I don't impose a sound on music or an instrument – I try to find its sonic nature. If you're recording Arvo Pärt's music, the weight of each single note counts. Tone and sound must derive from inside, the secret must be there – in the recording."

What has to interest him in a musician which makes him want to record them for ECM?

"I have to be touched, in some way. Something has to ring ... an aesthetical quality close to our ideas. There's no criteria, but in some way it has to feel that there is something there that we can develop. I don't want someone who's just on the market and famous or hip, or whatever. There's too much of that going on. We'd like to still do what we feel is a part of what we think and what we do. It can't be defined. It could be anybody who presents a project which has substance.

"We have no ideology and no strategies and we have no observer of the market, to look around and see what's going on. It comes and goes and comes and goes. I've been working with Jan Garbarek for 20 years, and if you realise the changes in the results one can see it was the right thing to do."

So what happens when Eicher goes into the studio for the first time with a new ECM-er? Is there preparation?

"Mostly nothing is prepared. I listen – sometimes I even listen to tapes, before we go into the studio. That's the place to work. In improvised music if people come together for the first time, you become part of that group if you're a good producer. Sometimes not much support is needed – then music starts to fly. Something takes shape. This happened with the Magico sessions in Oslo with Garbarek, Haden and Gismonti, where everyone came from a different place. In this case, as a listener you're part of the group. What we finally have is the musical documentation of everyone's input, including the engineer of course, if you have a guy with sensitive ears like Jan Erik Kongshaug.

"I like to do many things at the same time. Not only jazz, not only with written music. I want to do literature, too, and some small film projects. We've done Bruno Ganz reading Holderlin."

How does he decide if a record's successful or not?

"If you enjoy listening to it. If 'success' is a matter of sales figures to you, then I must say we've been lucky so far. When we made the first records, musically and commercially, it was a result of the liking of the music and the ability to capture the momentum of this music at the right time. The records I'm talking about were all made in Oslo at the beginning of the 70s: Chick Corea's Piano Improvisations, Jan Garbarek's Afric Pepperbird, Keith Jarrett's Facing You. The success of Paul Bley's Open, To Love was only musical. Return To Forever was a big surprise, totally unexpected.

"And yet, when you speculate with success, things might not work out as planned. Like when Pat Metheny tried to make American Garage as an American production. But if you do something on a spontaneous level of reacting to something you like, you do it much more honestly. With a magazine you can plan it to be successful, because you can study all the attitudes which have to be considered, in zeitgeist, in fashion or whatever. Magazines change their faces all the time. So do record companies. But I'd like to remain at least somehow away from all the negative influences, the daily idea of success, of being in with the trends. All those things don't interest me."

We are reaching an area that bothers Eicher intensely: the mass consumption of culture. There are no better places than London, or Munich, where ECM is still based, to appreciate this dilemma, and the producer is an articulate critic of a situation where every art form has attained a spurious excellence.

"Everybody seems to be successful. You go to a concert on Monday, there's a lot of people. You go on Tuesday, a lot of the same people. Everybody likes it. You go to the theatre in Munich – sold out every day. Everything's great, everybody likes it. Where's the resistance to something? Everything seems to be at the same level. I can't believe everything is good, that everything is so uncritically received these days. Is this a lack of sensitivity? There's a terrible neo-conservative movement which is embarrassing to me.

"More and more reviewers jump on the bandwagon to be in the stream of successful musicians. Less and less substantial critical reviews appear. I'd love to see critical reviews if they weren't just cold rhetorical ideas, or discrimination, or ideological stamps or even following fascistic or narcissistic tendencies – just to see something in perspective. The piles and piles of records and books reviewers have on their desk – they're not able to get the message. Now, with CDs, they just put the computer on and jump from one track to another. And that's where the superficial listening starts. Maybe we should only produce records with one track, like Arvo Pärt's Passio, which lasts for more than 70 minutes.

"In the 60s, think about the time a musician had to develop something, an idea, a sound. How many times did we have to wait until a Paul Bley came along? Now, a young musician plays an interesting note, he's hired to make a record and do a festival. He's exposed much too fast. He has no chance. And if he doesn't succeed, he's out of the window."

The complaint has become commonplace. But it's the key to Eicher's philosophy over ECM's direction. It might be strange that the man who brought the pastels of John Abercrombie, the exquisite organics of Egberto Gismonti and the cluttered roar of the Art Ensemble Of Chicago together under one logo should bridle at cultural homogeneity. Again, though, it's less the crossing of genres which is at stake, more the sapping of a music's inner strength. Eicher speaks of learning to "metaphorically look away", in order to tune out the deafening sound of so much music.

"You can't replace tone, or the breathing of notes. You can make notebooks, but if they appear on a record... we have done records like that too, and I can't listen to them. You can't replace interaction in art. That's what makes things move.

"I try to be resistant. I still consider our label to be able to listen to the echoes of, yes, another time. Think about the Lamentationes recordings of Thomas Tallis. I think I hear something incredibly contemporary in there. It may have come from the Middle Ages, but it's only possible to do it today as it really is. It's created its own form and sound and language. It came out of a long, long period of writing very complex music. With this, he arrived at being as simple as he could be, simple and yet – secrets in his music are still emerging. Even though I thought I understood everything, when I looked into the music, the score looks very simple – but there are so many secrets. The same with Mozart. There is so much to find and understand, and it has incredible strength."

Why aren't there more live recordings on ECM?

"We've done quite a lot. We did so much with Keith Jarrett, and yet quite a lot of it is unreleased. Ideally, one should be able to record without microphones. When there's a recording there's a different kind of consciousness to the musicians, and I really don't believe so much in live recordings. I'd rather be in the studio and develop something there, as live as possible. Pat Metheny's 80/81 is such an example.

"Many recordings have a lack of vitality because musicians, after a long tour, go into the studio and think they can recapture the intensity of a concert, but very often it turns out to be rather boring. We often do recordings before a group even exists. We get the group together and then they go out on tour. The Paul Bley Group, they started with Fragments, where they'd never played together before. After a year, they did another LP (The Paul Bley Group), and it's an amazing difference. I wouldn't want to say it's better, but it's a different experience."

It's a worthwhile point, for several ECM live recordings are among the finest by the players concerned - Jarrett's Köln Concert, or the Art Ensemble's Urban Bushmen, perhaps their best record.

"I agree. But you should know there was a lot of editing. I did a recording in Japan in '79 of the Belonging group with Keith and Garbarek. We mixed it just a year ago, and I sent it to Keith and he didn't listen to the tape for months. Now he listened and a few days ago he called me and said, I agree, we should release it.

"It was a fantastic concert. At the time, we felt they'd done better concerts. When we both heard it again, we both felt that this was just the concert. That's sometimes how it goes. From a distance, the perception might change. Other recordings we've done, I just can't listen to. They're boring. Too much is going on with the so-called 'live' experience. A bad note is still a bad note."

Perhaps ECM will become, in the eyes of its critics, more rarefied still. The leanings of the New Series and of "regular" ECM releases incline further away from Lester Bowie and Pat Metheny and other players seen as more red-blooded than some of Eicher's signings. He has lost Metheny and Bill Frisell to other labels; Jack DeJohnette and Steve Coleman may appear on ECM releases, but their own Audio Visualscapes and Sine Die were released elsewhere. If any of this bothers Eicher, it doesn't show. He is still trying to keep the whole catalogue in print, although he might think about trimming it down, "in two or three years".

Whatever happens, ECM is certain to maintain its isolation. Mention new age music to Eicher and he looks disgusted; "I don't know anything about it. I don't listen to it, don't know what it is. It's just another stupid stamp on music." If the market identified by Windham Hill is or was an ECM market too, Eicher simply doesn't care.

As far as this listener is concerned, if it weren't for Manfred Eicher's ECM, we wouldn't have had such masterpieces as Jan Garbarek's Dis, Eberhard Weber's Yellow Fields, Ralph Towner's Solstice, John Abercrombie's Timeless, John Surman's Withholding Pattern or Edward Vesala's Lumi. It's, well, as simple as that. He has put us all in his debt for recording so many unique voices with such intense faith and sensitivity.

"We're not doing enough," muses Eicher. "I think one needs new ideas to present a record today. We just make a record and put it in a cover and present it to the audience. It might be the most honest way, but I'm not sure if we can do just that, with all this traffic around. Advertising might help, but I don't think much about that. Discussion might help. Let's say, musics which are at least talked about, among friends."