How does an MP3 player work?

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The MP3 player market covers a range of shapes, sizes, features, storage capacities, file formats, and download services. Amid such variety, how are you to choose? That's where we come in. This guide will help you pick the perfect player.

What are my choices?
How does an MP3 player work?
10 key MP3 player features

How does an MP3 player work?

Find out what makes it possible for us to listen to a bunch of 1s and 0s.

The inner workings: Digitizing music | Compression | Playback | File formats at a glance

Digitizing music

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

A rough digital approximation of an analog sound wave

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 audio, especially portable audio. 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 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 analog-to-digital process. A digital audio device, such as an MP3 player or a computer sound card, uses a DAC (digital-to-analog converter) to turn the 1s and 0s back into an analog 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	Comments
AA	Audible, the format used by Audible.com, is designed for spoken audio content such as audiobooks and talk radio programs, including NPR. 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.
ATRAC3	ATRAC3 and ATRAC3plus are lossy compression formats used by Sony and its squadron of Network Walkman MP3 and MiniDisc players. It is an efficient format that sounds better than MP3 at the same bit rates. This format is akin to WMA and AAC but is generally known as a dark horse, as it is used by only Sony-branded players. Music downloaded or streamed from Sony's Connect music store are ATRAC3 files.
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 "lossy" 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 of digital music--so common, it's become shorthand for all portable players whether they use this format, though nearly all do. 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 what 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 checked 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, Yahoo Music, and Wal-Mart use secure WMA.

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What are my choices?

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10 key MP3 player features

How does an MP3 player work?

How does an MP3 player work?

Digitizing music

Compression

Playback

File formats at a glance

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