If you could always rely on Mercury Rev for one thing, it would be their interesting "arty" music that would never break out of its own cult-interest ghetto. A post-rock band who languished in the margins while those with less talent but more mouth hogged the limelight, Mercury Rev were the American version of Stereolab - brilliant and exciting in their own way, but never likely to get above number 57 in the charts.

However, continuing in their own wilfully weird fashion, they've just gone and released many people's album of the year in Deserter's Songs - which, if the hyperbole got the better of you, could be described as a Smile for the 1990s, but is in truth more like an indie version of a Walt Disney soundtrack with lyrics by Van Dyke Parks.

Sound strange? So is this band. Pick'n'mix from the following: the time they were banned from an airline because, mid-flight, the guitarist tried to remove the singer's eye with a spoon; the time when the bass player took the whole record company advance for an EP and went to Bermuda on a holiday without telling anyone; the time when the guitarist booked himself into a Jesuit monastery for six months to recover from a tour; the flautist who left the band to become a forensic scientist (just what did she see on tour to warrant that?) or the numerous incidents of nervous breakdowns, split-ups, fights and reunions.

If the lifestyle was a bit of a rock'n'roll cliche, the music was anything but. Early attempts to pin down their ineffable sound floundered somewhere around the "Pink Floyd meets Dinosaur Jr" stage while later attempts, such as Rolling Stone's pitiful "Dylan done by My Bloody Valentine", were wide of the mark. What is identifiable, in their sound, is the sort of sonic lineage that can be traced back to Sonic Youth and The Pixies with healthy doses of Pere Ubu and Wire in the mix; but the DJ John Peel sums them up best when he says "unlike many bands, you can't tell what's in their record collection". Complicating matters further, band members themselves say that their "here, there and everywhere" sound is a result of "whoever shouts loudest or has the biggest punch in the studio".

If there had been even the remotest hint of consistency in their work, they would have followed up 1995's magnificent See You On The Other Side album with further explorations of the Spiritualised/Stereolab take on "post-rock", more distorted guitars, fragmented keyboards, oblique lyrics, spacey samples and minimalist melodies. Instead they threw out most of their instruments, brought in harps, bowed saws, chamberlain strings and flugelhorns and swapped their Spaceman 3 and Jesus and Mary Chain albums for those by George Gershwin and Brian Wilson. They also drafted in Levon Helm and Garth Hudson of The Band to help out.

The result is their most beautifully melodious work to date: the amps are turned down, the harmonies are turned up and it's all a slow, subtle and swoonful affair. "We operate on a different time lapse," explains vocalist, guitarist and song-writer Jonathan Donahue (ex of The Flaming Lips, in case you're wondering), "as opposed to more popular bands who say `well, this is what the kids'll like in six months'. Our frame of reference is, at the very least, 45 years off. It takes a little bit of work, or just a slight acknowledgement that what went on before is valid in its own right."

But after having been in the vanguard of post-rock, surely they would have wanted to perfect that sound and beat Spiritualised to the tape? "Well, you just realise that you don't have to step on a distortion pedal all the time," says Donahue. "It's like when you're a teenager, you may put your hair in a certain way or wear certain clothing because you're not comfortable with who you are. "But when you get to 40, you don't care if your hair is falling out, you're like `fuck it, this is me' and it's exactly the same with music and musicians. All the way through this record we just said `what can we do better than what we've done before?' and we refused to take the easy way out. We really thought that now was the time for bowed saws and harps."

Deserter's Songs is an album that almost never came about, due to the fallout from their last tour. "On the day the last tour ended, I had a nervous breakdown which lasted for months, and people were interested in a lot of things besides the music - our drummer told us we were out of control and left (he has since returned), the guitarist Sean joined a monastery and the bass player, Dave, remained out of contact."

A switch of record labels, from Beggar's Banquet to V2, added to the confusion - but when Donahue and co-songwriter Sean Mackiowiak had written this new album, they found their exiled band members coming back, one by one, to go once more into the breach. How did the band react to the new songs, which are considerably more symphonic and melodious than anything you had presented them with before?

"We've always been pretty diverse in our musical tastes, so that helped," says Donahue. "There has some crossover between what we like, but for the most part everyone has their own little niche and none of them really go past the early 1980s. Sean's very good with the jazz and avant-garde of the 1950s, I just like the Delta blues and spirituals and Susie (Thorpe - flautist) knows classical music. We were, though, scared shitless making this record. We were doing a lot of things that for our band were very different - well, maybe for me not that different because I still have the demos we did before our first-ever album in 1991 and they sound pretty identical to Deserter's Songs. But at the time there was no record company who were ready to embrace the fact that you wanted to hire a string section or a trumpet player."

The first album, Yerself Is Steam, one of the definitive "art-rock" albums, did nothing for them in the US - but in Britain they were hailed as the saviours of American alterno-rock. Magazine front covers, numerous John Peel sessions and the support slot on a Bob Dylan tour left them dizzy: "a lot of things happened to us over a short space of time. It was a typical crash and burn scenario; every show was a case of somebody getting thrown out or somebody breaking something."

By the time of their second album, Boces, Mercury Rev had gone as far as they ever wanted to with arty rock and their sonic experiments were leading them down a cul de sac. "That album was just all noise, complaining and fighting," he remembers. "It wasn't meant to be the Metal Machine Music (the infamous discordant Lou Reed album) that it ended up being."

If anything, this new album will lose the band their "American weirdos" tag, which always prevented them from bridging the divide between critical acclaim and commercial sales. "We've always wanted as many people as possible to hear our records," says Donahue. "That doesn't mean I'm going to kiss someone's ass to make them like it - but it's a big misconception to think that we purposefully stay small and weird. We aren't weird, and I want a million people to hear this record."

Deserter's Songs is on the V2 label; Mercury Rev play The Mean Fiddler, Dublin, next Tuesday