how does an MP3 player work?
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.
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 | |
|---|---|
| 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 uses their own DRM (digital rights management) technology to secure some AAC downloads for iTunes, although portions of the music catalog are offered in an unprotected AAC format. The iPod is the solitary player that accepts copy-protected AAC files and only those from iTunes Music Store. DRM-free AAC files can be played on a growing number of devices, including Microsoft's Zune and Sony's Walkman series. |
| 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. After a long and frustrating war between competing file formats, most online music stores are now selling their music downloads as MP3 files, including Amazon, eMusic, Rhapsody, and Napster. |
| 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. Most non-iPod players support WMA, and some online music stores still use the secure WMA format (although the trend is changing toward sales of MP3 files). |
