It has been five years since MP3 blogs - also known as audioblogs - first started appearing on the web. In 2003, a few thoughtful music bloggers decided it would be a good idea to complement discussions of songs on their sites with the songs themselves, which readers could download in MP3 format and listen to straight away. Don't just take our word for it, was the attitude - take the music too.

The trend built slowly at first - Fluxblog, Stereogum and Said the Gramophone were pioneers - and then, over the last couple of years, it avalanched. Today, the blog index site Hype Machine lists more than 1,700 regularly updated MP3 blogs in regular use and there are certainly many more in operation. All musical tastes are catered to, and the music, much of it brand new or pending release, can be taken for free, no strings attached.

This is not, you might think, a development the beleaguered music industry can be watching with enthusiasm, but you'd be wrong. An New York University study published in February, Does Chatter Matter?, found that the volume of blog posts about a new album can significantly affect sales. Many record labels now view the audioblog as a vital marketing tool, and a euphoric plug on Brooklyn Vegan is more valuable in certain cases than a five-star review in Q. ('Certain cases' is worth noting; most blogs shy away from the mainstream, favouring obscure bands whose fans will also favour less obvious sources of information.)

In contrast to their disreputable cousins, file-sharing networks, MP3 blogs don't attract much legal attention. No one has been prosecuted for posting individual tracks. The most serious injunction a blogger is likely to get is a polite 'take down' notice, usually for posting material too far ahead of release. 'In fact,' according to Scott Wright, who runs the London-based blog Pinglewood.com, 'almost everything I post now is something I've been sent or asked to post by record labels or artists.'

'I draw the line at whole albums,' says Laura Seach, head of digital PR at Ninja Tune, an independent British record label, 'but if someone posts one track, that's great. The promotional opportunity is huge. We run campaigns now trying to get bloggers posting about our artists. You can't underestimate how important blogs are.' Rich Walker, head of communications at the Beggars label group, has a similar view. 'With certain bands, we allow one track to appear in the blogs in advance of a new album,' he says. 'It makes sense to send out the strongest one - we used "Fake Empire" for [Brooklyn indie band] the National. The track basically ends up playing the role of a lead single.'

By earmarking specific songs for blog use, the labels attempt to control how their music leaks. According to Walker, most of the 'better blogs, the ones with readership and clout', observe the rules of fair play and many sites voluntarily remove songs within a few weeks of posting. But, he acknowledges, certain bloggers, particularly those with clout, don't want to be part of a marketing strategy. 'All these publicists send me music,' says blogger Jace Clayton, 'but that to me is part of the blind idiot-machine of the music industry which I wish to have no truck with.'

Clayton, who posts a range of esoteric music on his blog Mudd Up!, is sensitive about the songs he posts and has made it easy for people to email him with objections. He understands the artist's perspective as he is a musician himself, trading under the name DJ/rupture. Does he mind when other bloggers distribute his music for free? 'I'd cringe if someone put my whole album up. But I'm happy if someone wants to post my songs or mixes. If I'm not on the blogs,' he adds, 'maybe I'm doing something wrong.'

The legal area they occupy may still be grey, but audioblogs represent a happy medium for industry and fans alike. The range of music available is marvellous, and yet there's something hugely appealing about being able to concentrate in detail on a single song - 'to get close enough to see the fingerprint,' as Clayton says, adding: 'Maybe the album is dead, but people love songs more than ever and hold them closer to their heart. That's what makes this pursuit seem worthwhile.'

Said the Gramophone

saidthegramophone.com

Founded by Sean Michaels in Montreal, March 2003

'Every other site is trying to break the world's greatest new band every day. We're just trying to find the greatest next three minutes of your life.' So says Sean Michaels, 26, who set up one of the very first MP3 blogs in Montreal five years ago. Today, Said the Gramophone is a revered elder among alternative music bloggers. Michaels and co-writers Dan Beirne and Jordan Himelfarb were talking about bands such as Arcade Fire, Beirut and Feist long before bigger sites and publications caught up with them. Not only that: they were eulogising them in an inventive, literary style. 'Because people can listen to the music while reading our text,' says Michaels, 'we can be a lot more free with our descriptions.' The site doesn't use advertising and is sponsored by readers through an annual fundraising drive.

Hot tips

Sister Suvi: 'A great band I'm posting about today. Lots of chanting and remarkable three-part harmonies.'

The Luyas: 'From Montreal. "Dumb Blood" is one of my favourite songs of last year.'

Hologram: 'An amazing Brooklyn folk band. I really like the song "Mommies".'

Most admired rival: shakeyourfist.blogspot.com

Mudd Up!

negrophonic.com

Founded by Jace Clayton in Madrid, December 2004

Jace Clayton already had a platform when he started an audioblog in 2004. As DJ/rupture, the Bostonian has been lauded for his politically charged music and inventive mixes, in which breakbeats collide with sounds from the fringes of black culture. Mudd Up! extends Clayton's preoccupations, which also include Arabic and Hispanic music, into text. One day he'll be posting an obscure hip hop track; the next his encyclopaedic knowledge will be brought to bear on digital Berber synth pop. 'Let's talk about one song in all its wonderful specificity, get close enough to see the fingerprint and try to figure out how this strange being came to life,' he says. 'I like bringing new stuff to the table and talking about it in an interesting way. It's not just MP3s that are being swapped but also musical information and context.'

Recently, Clayton has been spearheading a blogosphere-wide discussion of cumbia, a form of Latin-American dance music.

Hot tips

Grupo la Cumbia: 'Mystical and existential cumbia from a synthy Mexican boy band.'

Trim: 'The incredible Arabic sample on this grime track sparked a big discussion when I posted it.'

The Dream: 'People think it's bland R&B pop but 'Ditch That' is an amazing, epic song.'

Most admired rival: wordthecat.com/goku

Gorilla Vs Bear

gorillavsbear.blogspot.com

Founded by Chris Cantalini in Dallas, March 2005

'I just thought it was a cool way to share music with my friends,' says Chris Cantalini. 'I never thought anybody would read it.' He was wrong. His blog, Gorilla Vs Bear, now attracts 10,000 page hits per day and is the first port of call for anyone wondering what tomorrow's most exciting indie band will sound like. 'I don't really think about finding the next new thing,' says the 30-year-old, who was one of the first to write about acts such as Tapes 'n Tapes and St Vincent, 'but it's happened. Most of the mainstream music media - including Pitchfork - use blogs like mine as a filter these days, though they probably wouldn't admit it.' It helps that he lives near Austin, a major alt-rock hub and home of his current favourites, White Denim - although now, thanks to the blog, Cantalini has the clout to attract bands to play in his home town, Dallas.

Hot tips

Lykke Li: 'Brilliant Swedish singer. I think she's going to be huge.'

Paper Route Gangstaz: 'I've been playing the Diplo remix a lot on my radio show.'

Quiet Village: 'One of the best bands I've heard this year.'

Most admired rival: 20jazzfunkgreats.co.uk

Fluokids

fluokids.blogspot.com

Founded by François Arot, aka Pharrell, in Orleans, France, May 2005

This wildly popular music blog, loved and loathed in equal measure by Parisian hipsters, has become a phenomenon in France. Its contributors have used it as a springboard for putting on huge parties and establishing themselves as international DJs, and the word 'fluokids' is now used in the French media to refer to the trend of teenagers dressing up in fluorescent clothing. 'We created a monster,' says Hianta Cassam Chenai, one of seven contributors, all students, most of them based in Paris (see picture top left). They post dance-oriented music and have broken acts such as Brodinski and the Teenagers. The writing is insiderish and the blog's founder, Pharrell, cannily posts pictures of scantily clad girls to boost traffic. 'Some labels think that if they give us stuff they can control what we do,' he says. 'We don't really like that. We'll blog anything, just as long as it's catchy.'

Hot tips

The Shoes: 'We championed them early on. This is a great remix of the new Wiley track.'

Kris Menace: 'Magnifique.'

Laidback Luke: 'He's the best producer in dance music right now.'

Most admired rival: genevanheathen.blogspot.com

Pinglewood

pinglewood.com

Founded by: Scott Wright in London, February 2007

Compared to what's going on across the Atlantic, the British music blogging scene seems somewhat muted, but that's not to say quality is lacking. Scott Wright, a 31-year-old freelance writer based in London, posts at least five carefully chosen downloads per week. 'I'm the sort of person who makes mixtapes and compilations for people, and an MP3 blog is like a never-ending compilation,' he says. Each song is accompanied by small doses of literate and amusing commentary. 'My music taste is very broad. I listen to anything from hip hop to the Pixies. I just try to be irreverent and funny and not take myself too seriously.' If there is a policy, it's to post new music by bands keen for exposure. 'If I'm out and the second band on the bill is really good, I'll ask if they mind me posting their music. Usually they're really up for it.'

Hot tips

Micachu: 'Brilliant mix from 21-year-old wunderkind composer/songwriter/DJ.'

BLK JKS: 'They're from South Africa and they play heavy afro-rock with deranged guitars.'

Truckers of Husk: 'Like Battles, only Welsh. Thrilling, intricate experimental rock.'

Most admired rival: passionweiss.com