Digitising music

At their most basic level, digital music such as MP3s looks a lot like any other computer data file: a long series of 1s and 0s. In order to turn an analogue signal (such as one picked up by a standard microphone) into a digital stream, ADC (analogue-to-digital converter) software measures the signal at a regular interval to find the sampling rate. These samples, if measured close enough together, form almost an exact representation of the analogue signal so as to approximate the transmission using 1s and 0s that computers and MP3 players can read.

Compression

Each second of true CD-quality sound takes up more than 1.3MB of disk space, which is why file compression technology is essential to digital sound, especially portable audio playback. Using principles of psychoacoustics (how the brain perceives sound) and perceptual coding (eliminating imperceptible sounds), engineers develop algorithms, called codecs (compression decompression), that compress songs into the smallest possible sizes with a minimal loss of quality. The sound depends on two factors: the quality of this compression algorithm and the bit rate at which the song is encoded, measured in Kbps.

Playback

When you play a digital file, you essentially reverse the analogue-to-digital process. A digital audio device, such as an MP3 player or a computer sound card, uses a DAC (digital-to-analogue converter) to turn the 1s and 0s back into an analogue signal that can then be amplified and broadcast over headphones or speakers. The sound depends on the attributes and quality of the digital file, the DAC chip in the player, the amount of distortion and hiss added by interference from the device's other circuitry, and the audio output level of your headphones or speakers.

When a digital device plays music that has been compressed by a codec, software on its chip (called firmware) applies the codec to decode the file, then sends the decompressed 1s and 0s to the DAC.

File formats at a glance

The first format or codec to gain widespread acceptance was MP3, but there are now a variety of players on the market that support AAC, WMA, OGG, and other formats. This table will help you sort out the alphabet soup and determine which codecs you need in an MP3 player.
Format

AA

Audible, the format used by Audible.com, is designed for spoken content such as audiobooks and radio programmes such as those on Radio Four. Many portable music players support AA.

AAC

Advanced Audio Coding, developed by Dolby Laboratories and best known as the format used in iPods. Apple and Real use their own DRM (digital rights management) technology to secure AAC downloads for iTunes and Real Rhapsody. The iPod is the solitary player that accepts copy-protected AAC files and only those from iTunes Music Store.

FLAC

Free Lossless Audio Codec, an open-source format that uses a clever algorithm to preserve every 1 and 0 found in the uncompressed file. Though not widely implemented, lossless formats such as FLAC are popular with audiophiles who disdain formats (MP3, WMA, and so on) that further compress files.

MP3

Motion Pictures Experts Group Layer 3 is such a mouthful, it's no wonder the abbreviation has taken over. In fact, MP3 is the Kleenex or Hoover of digital music -- so common, it's become shorthand for all portable players whether they use this format or not. Nearly all do, though. The eMusic online music store and most file-sharing networks use MP3.

MP3Pro

The latest from Thomson/RCA (the company that licenses MP3 to manufacturers and developers), MP3Pro sounds better than MP3 at the same bit rate. However, it hasn't been widely adopted by manufacturers other than RCA.

OGG

Ogg Vorbis is the underdog of this group. It sounds great, and because it is open source, there are no licensing fees when it's used to encode or play music -- a fact that probably makes developers of other codecs a bit nervous. Although it's not as widespread as AAC, MP3, or WMA in players or online music services, OGG could gain traction as consumers grow more sophisticated in their digital audio usage and developers look for ways to cut down on licensing costs.

WAV/AIFF

This is uncompressed audio, like you'd find on a standard audio CD. For the most part, WAVs are found on Windows machines, while AIFFs live on Macs.

WMA

Windows Media Audio, Microsoft's format, sounds better than MP3 at the same bit rate. Some WMA files include copy protection, but others do not (if you left the 'Copy protect music' box ticked under the Options menu in Windows Media Player you've been ripping copy-protected WMAs). Most players support WMA, and online music stores such as Napster use secure WMA.

Hard-drive based players	Micro hard-drive based players	Flash based players
16Gb Sansa View MP3 Player	8GB Microsoft Zune	2Gb Netac A210 2" TFT MP4 Player
160Gb Apple Ipod Classic	2Gb Sansa Express MP3 Player	2Gb 2.4" TFT Audio Tech D883 MP4 Player
160Gb Archos 605 WIFI Portable Media Player	8Gb Apple Ipod Nano	2Gb Samsung Flash USB2 MP3 Player with FM