The bleeping noise in your head? That'll be Autechre...

In 1992, Warp records released their seminal Artificial Intelligence compilation, the album which redefined techno as music worth listening to at home, not just in clubs. They called it "electronic listening music"; everyone else called it "ambient" or "intelligent" techno. It launched the careers of Aphex Twin, Speedy J and Black Dog, but its two standout tracks were the debut releases by Rob Brown and Sean Booth, aka Autechre. Tomorrow sees the release of the pair's seventh album, Draft 7.30, and in the intervening 11 years they have continued to redefine what techno can be, rejecting its commonplace repetitive beats and systematically testing the conventional boundaries of rhythm.

"We've been getting more acquainted with rhythm," says Booth, "and it doesn't seem to limit us in the way it did when we first started ... Now I think we just get it, we're totally fluent in it and can be more expressive. I appreciate that these grids are there, but I don't want to have to stick to them. I like music that works around them or subverts them, where the listener has to work to find them." The poor listener is having to work harder and harder as their music becomes progressively more dense and complex. But once attuned to their idiosyncratic rhythmic sensibilities, he or she is rewarded with some of the most beguiling electronic music around.

Still, to the unprepared listener, Draft 7.30 could sound like the work of raging or deranged minds. But amazingly, Booth and Brown have kept their heads, despite spending so much time shut up in a room listening to electronic noises. "We argue a lot less," says Booth. "We used to be more egotistical, but I think you grow out of that after a bit."

The pair grew up in Manchester and met as teenagers through their participation in the city's nascent hip-hop and graffiti scene. Booth had been piecing together tapes of samples recorded from the TV and radio and editing them with the pause button; Brown had decks and a walkman: "Rob was more inclined towards layering, and I was more inclined towards serialism, but that was just because of the technology that we had." Pooling these limited resources, they began making music together in 1986.

As they got more equipment, and better acquainted with it, they started to synthesise more of their own sounds and rely less on samples. But they retain their love of hip-hop's do-it-yourself ethos, and Brown can still see the influence in their records of the early electro and rap music that used to circulate through their small network of like-minded schoolkids. "It would come compressed over radio airwaves and then [got] taped onto cassette, and it would be saturated in a weird way that wasn't intended by the producer. You could hear little ghosts or shimmers that you might be disappointed to find weren't there when you got the original 12-inch later on."

Such echoes and shimmers contribute much to the texture of Autechre's music. And it's the little ghosts they're looking for when they open up the backs of their machines and fiddle around inside. "You think you know everything about an instrument," Brown explains, "but then if you get the back off you realise that there's a little bit more under the surface that it's capable of, that the designers had limited with the amount of knobs they put on it." This refusal to adhere to the usual limits imposed by electronic instruments is what defines Autechre. "I love the physical dynamic of electronic sound, but too much sequenced music is all so bolted down," says Booth. They composed much of their last album by writing computer programmes which would generate inhumanly complex and unpredictable rhythms.

But making Draft 7.30, they returned to arranging their beats by hand. The result is their most challenging and formidably intricate set of rhythms yet. And if you're wondering where dance music comes into all this, don't worry. "I don't think in order to appreciate a piece of music you need to understand anything about it," reassures Booth. "You just have to hear it."

'Draft 7.30' is released tomorrow on Warp records