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Portable music players have come a long way since the Sony Walkman, so here's our guide to the latest models

The ready availability of digital audio players now means that users can easily become baffled by the sheer number of options. Not only do these devices allow hundreds, and even thousands of music tracks to be listened to on the move, but their differing capabilities mean that choosing the right one can be difficult.

You have to consider what music format is right for you, what type and quantity of storage is appropriate and how your choice will affect you in the long run. We've compared the benefits and drawbacks of 16 of the latest portable audio players.

We've also examined how good they sound, how easy they are to use, how easy it is to transfer your music and how the budget options compare with more established brands.

Player types
The portable audio player market can largely be divided into two. On the one hand are those products that use solid-state memory and on the other those that use a hard disk drive. Memory in solid-state players varies in size, but most commonly these devices offer between 64MB and 512MB of storage space. The Freecom Beatman Flash Recorder 512 is one such player and will generally store around 250 songs at near-CD-quality.

This type of audio device offers numerous advantages over CDs, tapes and Minidiscs since they allow users to carry a fairly substantial collection of music. They also contain no moving parts and are less likely to develop defects or skip tracks.

Some devices have a fixed internal memory as well as a memory card reader. If you've got a collection of Secure Digital (SD) cards, you can use them as a compact and durable alternative to CDs which are impractical to carry around and can be scratched very easily.

Solid-state audio players are typically very small and light, so they are ideally suited to those who live active lifestyles. They are very popular with fitness enthusiasts, because they aren't affected by bumps and shakes. They also use very little battery power, so can keep playing for a very long time. The I-River IFP-795 is the perfect example, as it can play continuously for a staggering 40 hours.

Hard disk-based portable audio players are a more modern phenomenon made popular by the explosive growth in popularity of the Apple iPod. Adopting hard disk technology for portable devices has been a great challenge for manufacturers. The sensitive components in a hard drive means there is a very real danger of damaging these devices with any sudden movement or impact.

Most hard disk players now wisely do not play music directly from the disk. Instead, music is streamed into an internal buffer memory, which allows songs to be played while the hard drive goes into hibernation.

This reduces the likelihood of songs skipping, but more significantly lowers the risk of the hard drive being damaged by jolts. The iPod, for example, has 25 minutes of skip protection but even so, Apple does not recommend you do vigorous exercise while operating one.

The major advantage of hard drive audio players is their sheer capacity. The Creative Zen Xtra offers 60GB of space. This is enough to store around 15,000 songs, or three different albums every day for an entire year.

Unfortunately, the amount of power required by a hard drive audio player is significantly greater than that of solid-state players. High-quality music that has been encoded at high bit rates is a big drain on battery power. Most power, however, is consumed by the hard drive, which uses a motor to spin the disk and move the read/write heads.

Most hard disk players will give you enough playback time to last through the day but, as is the case with the iPod Mini, you'll probably need to recharge these devices on a nightly basis. Manufacturers have tried to combat the problem of high power consumption by using larger batteries, but this adds weight to the player, which is hardly a desirable factor in a portable device.

Sound quality
Not all portable audio players are created equal. One important factor is the output power, quoted in milliwatts (mw). In short, the higher this number, the more powerful the sound from your portable audio player. This does not have much bearing when they are used with ordinary headphones but, if you decide to connect your portable audio player to a set of ordinary speakers at home, you'll want to make sure it has a decent amount of output power, unless you use powered speakers with a built-in amplifier.

Earphones also play a significant role. A poor set of earphones will usually give poor-quality sound (limited or spiky frequency response) and will probably have a low sensitivity, so you'll have to increase the volume on your audio player to make it play at an acceptable level.

The final consideration you'll need to make is the signal-to-noise ratio (SNR) offered by each portable audio player. An SNR is said to be favourable when the signal (required audio) is clearly distinguishable from the noise. For example, there is a noticeable difference in sound quality between the Aiwa HZ-WS2000 (80db SNR) and the Creative Zen Touch (97db SNR).

File formats
When most people think of portable audio players, they think of mp3. The mp3 compression format, a contraction of the term mpeg-1 Layer 3 Digital Audio, was developed by the German Fraunhofer Institute as a solution to the problem of storing high-quality audio at small file sizes.

The benefits of sound compression are numerous. Uncompressed CDs using the 16bit 44KHz PCM (pulse code modulation) wav format sound excellent, with a broad frequency response and little unwanted noise. Unfortunately a single track can occupy a lot of space, so the average CD is limited to storing just 74 minutes of music, enough for just one album.

Compressing audio with formats such as mp3 allows users to enjoy CD-quality music that takes up significantly less space. Unfortunately compression, by its very nature, removes parts of the sound.

Thankfully, advanced compression methods mean a CD full of mp3s can store around 10 times as many tracks as a standard audio CD, without seriously compromising quality.

Mp3 is a well-known technology, but there are numerous other compression formats that achieve similar results. The suitability of your portable audio player depends largely on its compatibility with these formats, since they determine the quality and quantity of music that can be stored.

The wma (Windows Media Audio) format was developed by Microsoft as a response to mp3. It is supported by all PCs that use Windows Media Player, and its effectiveness in reducing audio file size is well proven.

Many believe that wma offers better sound quality than mp3, and there are many portable audio players that use this format. In practice, the difference in audio quality between mp3 and wma is negligible, and often comes down to personal choice.

The main difference between the two formats is their Digital Rights Management (DRM) capabilities. DRM is an essential element for music vendors, since it affords their products a degree of copyright protection.

Tracks encoded in the wma format can be protected by DRM and, when so protected, cannot be freely distributed. Users must purchase a licence in order to play them, and they often can't be copied. The music industry says this protects recording artists from the scourge of illegal file downloads, but the downside is that you may be unable to share the odd track among your friends.

Until recently the mp3 format was devoid of all DRM. Fraunhofer has developed the LWDRM (Light Weight Digital Rights Management) system but it hasn't gained widespread acceptance yet. Most commercial software still allows users to create an unlimited number of unprotected mp3 albums on CD. These can then be distributed and read by a wide range of players.

Portable audio devices have historically supported mp3, but many are now focusing on formats that offer DRM. The Apple Ipod can play mp3s, but you can only buy songs from the Apple iTunes Music Store in the proprietary Apple Audio Coding (AAC) format.

The future of DRM
Microsoft has recently unveiled a more modern vision of DRM for wma audio. Previously called Janus (the Roman god of doorways), this technology promises online vendors greater control over music than was previously possible.

A Janus-enabled audio file can offer a high level of copyright protection, even when copied to an individual's audio player. This technology will enable online music services such as Napster to give subscribers the choice of copying music from their PC to a portable device without the risk of it being passed illegitimately to other users.

This form of DRM should, in theory, lead to a more diverse range of options for downloading music, since it allows vendors to distribute audio that is restricted in many ways. Songs can be time-limited to facilitate downloading sample clips, or they can be limited to a specific number of plays. This lends itself well to services that want to allow customers the option of 'renting' individual songs for less than it would cost to buy them outright.

Most audio players aren't Janus-compatible. The iPod and iPod Mini use Apple's proprietary DRM techniques, and do not support any sort of wma playback. Some existing players (such as the Samsung-Napster YH-920 GS) are firmware upgradeable and may be able to support Janus DRM after a software update.

Forthcoming players are likely to be compatible from the outset. The technology can also be applied to other hardware. Janus may soon become widespread among Portable Media Centers, Windows Mobile-based Pocket PCs, smartphones and devices connected over a home network.

Music download services
Now you're a little closer to choosing a digital audio player, you'll probably want to know your options for filling it with music. The most basic method (although still technically illegal in the UK) is to encode your CD collection using software bundled with your chosen device.

Another method is to download music from the internet. There are a number of websites that offer free mp3 downloads, but many of them are illegal since they violate copyright laws. Arguably the best method, however, is to use a legitimate download service to keep your music collection up to date.

Napster
www.napster.com
Possibly the most well-known music download service is Napster, which has undergone a dramatic change since its illicit origins. Today, there are two types of service available, the most basic of which is Napster Light. The Napster client is supplied with some players, such as the Samsung-Napster YH-920 GS, but it can also be downloaded via the internet.

This means you can arrange and synchronise audio files with your music player, as well as download new songs from a database of over 750,000 titles. Individual songs cost approximately 99p, with complete albums starting from £9.95, which compares favourably with high-street prices.

You can also try before you buy, since most tracks can be played as a 30 second preview clip. Music you have purchased can be burned to a CD, copied to your audio device, or played on a PC, but Napster only provides music in the wma format. If you've got a music player that does not support wma, you'll need to convert to mp3 first.

The full Napster package requires a subscription. For £9.95 per month, you get access to the same library of 750,000 songs, all of which can be listened to in full at no additional cost. Tracks can be streamed directly from the Napster music server, or saved on your PC for listening offline.

Users may collect as many tracks as they want, but there is a limit to the number of PCs you can use to access them. If you are a frequent traveller with access to several computers, think about which three computers you're most likely to use.

Unfortunately, until Janus technology becomes available, you'll need to pay an additional fee if you want to permanently save or transfer any of your music to a digital audio player. The monthly fee doesn't entitle you to ownership of the music, so any tracks you've downloaded will become unusable when your subscription is terminated.

If you've collected a vast amount of music, this could be hugely frustrating. Tracks can be downloaded at the same cost as those on Napster Light, but subscribers are entitled to a discount of up to 10 per cent (paying around 88p per track) when buying more than one song at the same time.

As a whole, the service has a wide range of music and provides some interesting benefits over its competitors. One of its strongest assets is the option to browse the music collection of other Napster subscribers. So if you discover another user has similar music tastes, you can pick up ideas on what songs to listen to.

iTunes
www.apple.com/itunes
ITunes is arguably the world's biggest legal music download service. It has a library of over one million songs from artists on all five major record labels, and tracks from over 600 independent labels. It works in much the same way as the Napster Light service, in that it uses client software that acts as a music organiser and download service.

Songs can be searched for using common criteria such as artist or genre, and they all have a 30 second preview. ITunes has recently adjusted the price of owning music, so tracks can now be bought for 79p each and full-length albums for £7.99.

ITunes can be used by anyone with a PC, and can play music encoded in various formats, including mp3. Unfortunately the service is geared towards iPod owners, and downloads are only available in the AAC file format. You can still make use of iTunes as an alternative to visiting your local music store, but it is directly compatible with relatively few portable players. You could burn music onto a CD, but this limits the potential of the service.

Other music download services are available but some, such as Sony Connect, only supply music in proprietary audio formats. In other words, not all audio players work with all music download services.

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