Though not exactly obscuring the achievements of a 25-year career as pioneer of synthesised sound, the operation through which Walter Carlos changed gender and became Wendy Carlos has always carried with it that element of sensationalism which has threatened to sideline her contribution to contemporary music. And that contribution has been considerable. Though latterly regarded as something of a novelty album, the impact of Switched On Bach on an unsuspecting world back in 1968 cannot be overstated. Simply put: for many of the millions of people that heard it, it was the first use of pure, electronic sound as a credible means of producing music.

It couldn't have happened at a more opportune moment. Electronic 'music' was, seemingly, still held in the stranglehold of the experimentalists - Stockhausen, Cage, Berio et al - whose apparent rejection of anything that could be considered to have 'entertainment value' had effectively restricted its appreciation to a small group somewhere at the margins of the avant-garde. Unlike many of her contemporaries working with electronic sound, Carlos apparently had no desire to 're-invent' music through new forms of notation, the introduction of random elements, or the reliance on chance, and was content simply to readjust our perception of what could be achieved through the processing of sound from electronic sources.

The release of Switched On Bach dovetailed perfectly with (indeed, was prompted by) the development of the music synthesiser - in this case the Moog - and in many ways acted as the catalyst for the interest which was starting to surround this new and exciting departure in instrument technology. The choice of Bach concertos as the album's musical source was equally inspired. It carried with it the respectability that could only come from music written by one of the world's greatest composers, yet didn't place undue expressive and dynamic demands on an instrument still at a relatively early stage in its development.

Classically trained in music at Brown University and physics at Columbia, Carlos went on to become the first person to use vocoders - in the film score for Stanley Kubrick's A Clockwork Orange - and predated 'new age' music by more than a decade with environmental/ambient compositions like Sonic Seasonings. After writing scores for Kubrick's The Shining and Disney's Tron, Carlos successfully replicated an entire philharmonic orchestra, using additive and FM synthesis, on 1984's Digital Moonscape. And the ground-breaking continued with the album Beauty In The Beast, an exploration into alternative scales and tunings based on the music of Bali, India, Bulgaria, Africa and Tibet.

Carlos' most recent work is Switched On Bach 2000, a reworking of the compositions included in her original 1968 recording using current techniques in computer sequencing, digital recording and editing, and digital synthesis. (Actually, as a challenge to those who think they have sharp ears, Wendy included one analogue Moog synth patch from the original recording.) The work is a culmination of all of her past creations, and a stunning vindication of the power of modern instruments. The timbres she has created are both breathtaking and bizarre, and yet life-like in character...

The instruments on Switched On Bach 2000 sound incredibly subtle. Are you using any samples or PCM-based sounds?

"Oh no!"

So it's all synthesised?

"The sounds I've done, I've taken the time and made recordings in Bali and Java of actual instruments, and I've played them and A/B'd back and forth for weeks and weeks. I did all the modulations that would match, and did Fast Fourier things in trying to produce voices that come close. Some of the sounds are quite close, some are not so good, but when you play them together, the ear suddenly thinks, 'Ooh, it sounds right.' It's like computer graphics: when you have enough things happening, you overlook the little flaws. So it sounds happening.

"The truth is PCM is a nice quick, cheap and dirty way to get certain effects with the least amount of work. Occasionally, when I've done orchestrations for film scores and the like, I'm not beneath adding in a little bit of a sampled tambourine or a cymbal roll, or perhaps even some kind of a trombone bite lip sound that's on one of the Kurzweil 1000 modules. If it's mixed in properly, it can give a touch of authenticity on certain discrete notes. But you have to be very stingy with those things because they end up sounding like TV scores."

A lot of the individual timbres sound detuned, with the pitch fluctuating and odd harmonics rippling out...

"Yeah. Polynesian instruments actually; most percussion instruments do not have one long dimension. A violin has one long dimension, the string is thin and it's long. A flute has basically one dimension, it's a narrow tube that goes on for a couple of feet; the clarinet's the same way. Most instruments that are long and thin produce the kinds of waveshapes that we're taught in schools and in books; the first overtone is the fundamental, the second one is two times that, the third is three times it.

"That's sort of true for the piano, though the strings are a little thick for their length at the high end, so you'd expect their overtones to get sharp, and they do. That's why a good piano tuner makes the high notes higher pitched than they normally should be.

"Percussion instruments have two dimensions instead of one. They have very odd overtones, but they are controllable, sensible overtones. The first partial might be something like 200Hz, so think of the number 2. The next would be 5, so it's not doubled, it's something like 2.5 times the fundamental; and the next one might be 8, and the next one 11.

"So, you look at the overtones and think of them as the second harmonic, the fifth harmonic, the eighth harmonic, and the eleventh. You'll find that produces the effect of things like xylophones and marimbas. When you're doing additive synthesis and complex FM, you find quickly that there are a lot of these families of different types of pitch intervals that produce some wonderful sounds, and can sound like acoustic instruments that have thickness or width or other physical dimensions in their vibrating apparati."

Do you ever create sounds from instruments of some imaginary shape?

"Absolutely. A lot of the sounds on this recording came from having first found how to get a very decent sounding tam-tam or marimba or glockenspiel. Once you've made these sounds, and you store them, you can start to think, 'Hey, if I made these a little further apart in the overtones, what does that do?' Or, 'If I gave this one an extra peak in the middle of its overtones, what does that do?' And you start playing almost as though you're cutting the metal with tin snips, building things out of wood and brass, putting together new instruments. But you're doing it in a computer, simulating what would happen.

"You find yourself coming up with new families of sound that are unlike anything you've ever heard before, except it sounds vaguely as though you've recorded some live thing rather than just a quick cheap and dirty set of oscillators being thrown together. They have a real instrument quality. There's a sequence. There's a sophistication to them."

Is there anything you think needs to be developed? Do you find any recurring shortcomings when you're trying to create sounds?

"Always has been. Always will be. The current ones on my hate list are: no one has built a brand new, big complex FM and additive synthesis engine. The best one out there is the SY series, or the TG rackmount versions. But most people are still using sampled waveshapes.

"With the Kurzweil 2000, at least there you've got a big family of very rich multisampled sounds and sampled analogue waveshapes, and sampled digital waveshapes, and a very fancy engine for combining them and controlling the nuances of vibrato, the chorusing, the enveloping, the filtration and making it MIDI controllable. That's very powerful stuff.

"At the same time, it's like you never saw a way of making real colour images, but instead were content with using pen and ink. You can still be an artist, you can still do something splendid, but it's kind of avoiding the fact that really, to get at the sounds, what we've still got to do is get at every overtone and start digging with the parameters.

"We're still in growing pains. Y'know, it's really a young field. It's only a few decades old, and it's easy to lose sight of that. It hasn't been around for a long time like the piano or the orchestra or the blues guitar. You have to give it some time. They're changing the rules every day. We still don't know where we're going.

But geez, it takes my breath away to see what we can do right now. Desktop audio. Desktop video. All of these things are getting to the point where you could probably spend twenty or thirty years producing a one-hour visual/audio extravaganza; making every frame, every note, every reverb pulsation by hand, yourself, one person working alone."

The CD booklet says that Switched On Bach 2000 took 3000 hours to create?

"Well, I guess I was a little bit self-conscious. I knew that if I didn't make this quite polished, some people would hold it up to me. When you do something like that, you're less free of spirit than when you're doing something brand new. So I'm looking forward now to doing something with a little more censure, and discovery and freedom."

Are you getting into video now?

"I'm hoping to. I used to be an amateur artist - though I've never trained in it so I'm very aware; I don't much care to be a dilettante. If you're gonna do something, you learn a lot about it and do it right. But that's my attitude. Anyway, yeah, I would like to get into doing computer graphics, and PhotoShop and all of that. But at the same time, I'm trying to get back at doing some original composition."

You used the new Dolby Surround Sound on this album?

"Yes. Did you hear it? Full logic, and if you play it on a good system, you'll see that particularly the Toccata & Fugue just dances all around the room."

Did that take long to do?

"It was one of the harder things. I had to sit down and take the score and break apart every note, every phrase. The whole thing is just filled with pencil everywhere, saying, 'This note goes to the left front. This one goes centre. This one's to go to surround and to right rear.' Everything. You've got all these instructions. My God! Trying to put that together on a multitrack you feel like you're building teeny-weeny jigsaw puzzle pieces to make a whole mural on a wall or a Sistine Chapel ceiling.

"It seems to take a long time, but when it's done you stand back, and you don't even know what quite to expect. It takes your own breath away because you've been so close up that when you stand back you don't recognise it again. I think of the painters of things like the Renaissance paintings - you know the ones that cover the entire wall of a church - there they are on their scaffolds, getting a good face, a good eye, a good fingernail. Then they stand back, and it's like, 'Whoa! What is that?' It's a nice feeling. It's where you get your kicks when you're working alone."

Do you use MIDI automated mixing? I saw the JL Cooper FaderMaster in your equipment list.

"Yeah, but I don't use it for mixing. I usually play my mixes live. Maybe I'm an old timer that way, but I find that a lot of the other new approaches are making for a fairly sterilised, antiseptic kind of music. It's not where my heart is. As much as I am a technophile, my real love for the arts, be they visual or aural, is in the human side. You know, it's fine to have the tools to do it, but if you make stuff that sounds like it was generated by computer, that has the heart and soul of a 68040 chip or something... who wants that?

"I try to use hands on, interactive feeling and emoting, rather than planning it out cerebrally and concocting it all with the left hemisphere. I try to fly by wire a lot, and then go back and edit, and throw away huge quantities of this stuff, keeping what seems to have been the magical moments.

"It's the question of personal integrity. You have to be a little obsessive, and a little bit aware of things as a left-hemisphere person. You have to know what you're doing. But after that's all done, you put the driver in charge as being your soul, your emotion, your gut, your intuition."