Most clients are happy with us sorting out this level of detail, but for those who want to research this area here’s some background information on digital music files.

CDs are a good starting point as they contain the maximum amount of data. Therefore they will give the best quality sound. If you simply replicate a CD on your computer the file you would have is a WAV (or .wav) file.

This file would be exactly the same size on your hard drive as it is on the CD – about 700 MB. It is ‘uncompressed’ – a technical term which indicates that no data has been removed. The advantages are that this offers the highest possible quality, but you’d need a lot of disc space, and playing WAV files on a portable player would rapidly flatten its battery.

Another significant disadvantage of a WAV file is that it doesn’t contain any of the album, artist, track and genre data you see in iTunes. Yes, the data is there, but its held in iTunes own database. This is fine when you rip onto your own computer and use that to sync with your own iPods, but it makes moving files from one PC to another exceptionally difficult.

Enter AIFF. This is the same as a WAV file (in size and quality) but has a header which stores vital music data (sometimes called metadata). This means an AIFF file created on one machine can be imported into iTunes on another along with the vital data about artist, album, composer etc.

To save space and improve battery life people typically opt for smaller files – compressed. You can opt for lossless compression or lossy compression. As the name implies lossless aims to lose nothing of the sound quality (but the files are bigger) while lossy compression throws something away, but saves massively on file size. Compression is described further here.

iPods support Apple’s own lossless compression (Apple Lossless) and get very high quality audio in files about half the size of the original WAV.

Lossy compression is the facility that enables Apple to claim your iPod will store 7,500 songs or more. iPods support both MP3 and Apple’s own lossy compression format – AAC.

What’s the difference between MP3 and AAC?  Put most simply,  AAC is a better way of compressing music and so sounds better.  Apple claims an AAC music file sounds as good as an MP3 file containing 30% more raw data. AAC also supports 48 full frequency audio channels, MP3 just two.

MP3 files have one major advantage – they’re the lowest common denominator of the music player world. Sony, Philips, Rio, Samsung – they all support MP3 while AAC is effectively an iPod standard.

Which format should you opt for? If you want uncompressed files select AIFF. If you want a compromise – high quality but smaller files – try Apple Lossless.

If you want to maximise the capacity of your iPod, go for compressed AAC files. If you want to keep all your options open, MP3.

Footnote
WMA? Windows Media Audio is Microsoft's proprietary format. It is not supported on Apple iPods, which for many people reduces its popularity. It does have built-in digital rights management (DRM) which has made it popular with online music stores such as Napster.

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