We woke up this morning with those MP3 blues

With 30 legal music sites, all charging different rates, downloading tracks in the right format at the right price isn't easy PC. Emma Lunn untangles the web

Does a great riff sound better when it costs you pence to buy instead of pounds?

Music lovers might argue that it sounds the same however you listen to it, whether on vinyl or CD or as digital files on a computer. But as internet sites offering cheap music downloads mushroom, those fans keen to update their collection are increasingly going online to get hold of music ranging from the Clash to Coldplay to U2, whose song "Vertigo" was the soundtrack for an iPod ad campaign.

Low-cost downloads have come out of nerds' bedrooms and into the mainstream - they were included in the official Top 40 chart countdown for the first time in April. Their emergence has been responsible for sparking a music price war.

While you can pick up Coldplay's new album for £9.99 instore at HMV, you can save yourself £2.04 by downloading it from a Napster website.

The saving rises to £3 if you buy from the online retailer CD Wow! - including post and packing. But spot another chart CD in Tesco at the full price of £9.99, and you can pick it up for £6.97 - 2p less than on CD Wow! - as part of a promotional deal.

But it isn't just a question of shopping around, as what you pay for your music now depends as much on the way you listen as where you get it from. Surging sales of iPods and MP3 players, both of which let you listen to a digital version of a song, suggest downloading is the way ahead for people with their ears to the ground, but a question mark hangs over how much value they really offer.

There are now more than 30 legal download services based in the UK, offering millions of tracks for sale, and the choice can be confusing.

For the uninitiated, music files can be downloaded from the web in various digital formats, most commonly MP3. Once you have stored them on your computer using specialist "on-site" software, you usually have a choice of burning them on to a CD or saving them into a portable player.

The cost depends on the site and on the speed of your internet connection. If you have broadband, it will take around 50 seconds to download a CD, compared to five minutes with a dial-up connection.

Much will depend, too, on how many songs you are looking to buy, and whether you're prepared to subscribe to a service or want to pay-as-you-go.

For example, Napster - once outlawed but now a fully legal service - offers a standard subscription deal for £9.95 a month. This allows unlimited downloads from its library of over a million tracks.

But the songs can only be played on your PC; it costs a further 79p per track to burn them on to a CD or transfer them to a portable player. So you can only keep the music for ever if you pay the extra 79p per track; cancel your Napster subscription without first transferring your choice and you lose access to the music.

Fewer restrictions apply with the Napster To Go subscription deal, which costs £14.95 a month. The difference here is that any number of songs can be transferred straight to a compatible MP3 player such as an iPod.

But cancel your subscription and, once again, you'll lose access to those songs you've downloaded while a member.

Note also that if you transfer tracks to an MP3 player from the website, the Napster software will demand that you hook up every month to refresh its memory and access the copyright agreements attached to the tracks; otherwise you lose access.

The rival Wippit.com website, which also operates a subscription service, offers the best value if you want instant access to a lot of songs. This yearly £50 deal allows you to download up to 60,000 tracks - and keep them. Wippit currently has a bank of 600,000 but lets you access only 10 per cent at any one time.

However, for individual tracks and albums, pay-as-you-go could work out cheaper. Apple's iTunes charges you 79p per track and from £7.99 for an album. (These charges are virtually the same as on a third Napster service, the pay-as-you-go Napster Light.) But watch out - tunes downloaded from iTunes will play only on Apple software on your machine or on an Apple iPod. They cannot be transferred to any other MP3 player.

Researchers at Which?, the consumer watchdog, assessed 10 download sites, including Napster, Wippit, Streetsonline and Mycokemusic. Judged on value for money, ease of use, sound quality and range of music, iTunes came out top, although it was criticised for charging customers in Britain 20 per cent more than in the rest of Europe.

On Mycokemusic, which was launched last year by the Coca-Cola Company, you buy credits and get more of these for your money if you buy in bulk. For example, £40 will get you £50 worth of credits. But since tracks are quite cheap to download at 99p each, you will often end up with credits left over.

Always check each website's restrictions on how you can use tracks, known as digital rights management. Some sites let you burn a track on to a CD as many as five times; others will allow this just once.

And check, too, that you are allowed thousands of downloads; some broadband subscription deals impose limits, above which you will be charged extra.