A digital audio player (DAP), more commonly referred to as an MP3 player, is a consumer electronics device that stores, organizes and plays audio files. Some DAPs are also referred to as portable media players as they have image-viewing and/or video-playing support. MP3 players are now regularly built into mobile phones, making them the most common form of digital audio player. In short, an MP3 player is a portable device that plays digital music files–although many MP3 players can do much more than that. They evolved from the portable cassette and CD players that we carried around in the 1980s and ’90s. Instead of bulky cassettes or scratch-prone compact discs, most MP3 players play files stored directly on the device. Aside from a pair of headphones, there is nothing extra you need to carry to enjoy your music collection.

An MP3 is a digital audio file compressed with a standard defined by the Motion Pictures Experts Group (MPEG). MPEG was formed to develop techniques for dealing with digital video; since most video also contains audio, MP3 was developed as an audio extension of that work. Officially known as “MPEG-1, Layer 3″, MP3 is a lossy compression algorithm that uses psychoacoustic modeling to reduce the size of audio files by up to 90%.

Psychoacoustics takes advantage of deficiencies in the human hearing system to throw away digital bits corresponding to sounds that cannot be heard. The human ear cannot hear soft sounds in the presence of loud sounds having a similar frequency; for example, a voice conversation becomes inaudible when a jet flies low overhead. This effect is known as auditory masking, and done correctly the discarded sounds will not be missed.

MP3 is a lossy algorithm in the sense that the original bits cannot be recreated from the compressed bits. In terms of hearing, however, MP3 is lossless because the human ear cannot distinguish between a CD recording and a properly encoded MP3 version of it. MP3s achieve this transparency at a bit rate of approximately 256 kilobits per second, or roughly one sixth of the 1.4 megabits per second required by the compact disc format.

MP3s can be recorded at lower bit rates, saving even more space, but audible differences begin to appear at rates below 128 kilobits per second. At these lower bit rates, MP3 can use a trick known as joint stereo to improve quality. Audio generally consists of left and right audio tracks. Joint stereo combines, whenever possible, the sounds common to both left and right tracks into one track. Instead of left and right, it has “common” and “different” channels.

Being an open standard, and therefore available to anyone, has played a major role in the widespread adoption of the MP3 file format. While specific implementations such as those by the Fraunhofer Institute may be protected by patents, there exist numerous open source implementations. MP3s were originally only playable on computers, but inexpensive, portable MP3 players such as Apple’s iPod have since been developed.

History

The immediate predecessor in the market place of the digital audio player was the portable CD player, which was sometimes referred to as a “portable audio device.”

Briton Kane Kramer designed one of the earliest digital audio players, which he called the IXI. His 1979 prototype was capable of approximately 3.5 minutes of audio playback but it did not enter commercial production. The related patents expired in 1988. Apple Inc. hired Kramer as a consultant and presented his work as an example of prior art in the field of digital audio players during their litigation with Burst.com almost two decades later.

The first mass-produced DAP was created in 1997 by SaeHan Information Systems, which domestically sold its “MPMan” player in the middle of 1998. The South Korean company then licensed the players to Eiger Labs which distributed them—now branded as Eiger Labs MPMan F10—to the North American market during the summer of 1998. The flash-based players were available in 16 MB storage capacity.

The Rio PMP300 from Diamond Multimedia was introduced in September 1998, a few months after the MPMan. It was a success during the holiday season, with sales exceeding expectations. Interest and investment in digital music were subsequently spurred from it. Because of the player’s notoriety as the target of a major lawsuit, the Rio is erroneously assumed to be the first DAP.

In 1998, Compaq developed the first hard drive based DAP using a 2.5″ laptop drive. It was licensed to HanGo Electronics (now known as Remote Solution), which first sold the PJB-100 (Personal Jukebox) in 1999. The player had an initial capacity of 4.8 GB, which was advertised to be able to hold 1200 songs.

In October 2001, Apple Computer (now known as Apple Inc.) unveiled the first generation iPod, the 5 GB hard drive based DAP with a 1.8″ Toshiba drive. With the development of a minimalistic user interface and a smaller form factor, the iPod was initially notable within users of the Macintosh community. In July 2002, Apple introduced the second generation update to the iPod. It was compatible with Windows computers through Musicmatch Jukebox (now known as Y!Music Musicmatch Jukebox). The iPod series, which grew to include microdrive and flash-based players, has become the market leader in DAPs.

In 2002, Archos released the first “portable media player” (PMP), the Archos Jukebox Multimedia. Manufacturers have since implemented abilities to view images and play videos into their devices.

In 2003 the first MP3 players were installed into mobile phones in South Korea and the first artist to sell songs as MP3 file downloads directly to mobile phones was Ricky Martin. The innovation spread rapidly and by 2005, more than half of all music sold in South Korea was sold directly to mobile phones. The idea spread across the globe and by 2005 all five major handset makers, Nokia, Motorola, Samsung, LG and SonyEricsson had released musicphones. By 2006, more MP3 players were sold in musicphones than all stand-alone MP3 players put together. The rapid rise of the musicphone was quoted by Apple as a primary reason for developing the iPhone. In 2007, the installed base of musicphones passed the 1 billion level, and today more than half of all moblie phones in the world have an MP3 player.

Although online music services such as RealNetworks’ Rhapsody also offer legal downloads through a subscription plan, the launch of the iTunes Store in 2003 established the model of selling individual songs and albums for purchase.

Operation

Digital sampling is used to convert an audio wave to a sequence of binary numbers that can be stored in a digital format, such as MP3.

Common features of all MP3 players are a memory storage device, such as flash memory or a miniature hard disk drive, an embedded processor, and an audio codec microchip to convert compressed sound into analogue form that is then played through the speaker jack.

Most DAPs are powered by rechargeable batteries, some of which are not user replaceable. Listening to music stored on DAPs is typically through earphones and stereo systems connected with a 3.5 mm jack.

Types

Digital audio players are generally categorized by storage media:

Flash-based Players: These are non-mechanical solid state devices that hold digital audio files on internal flash memory or removable flash media called memory cards. Due to technological advancements in flash memory, these originally low-storage devices are now available commercially ranging up to 32 GB. Because they are solid state and do not have moving parts they require less battery power and may be more resilient to hazards such as dropping or fragmentation than hard disk-based players. Basic MP3 player functions are commonly integrated into USB flash drives.

Hard drive-based Players or Digital Jukeboxes: Devices that read digital audio files from a hard disk drive (HDD). These players have higher capacities currently ranging up to 250 GB. At typical encoding rates, this means that thousands of songs can be stored on one player.

MP3 CD Players: Portable CD players that can decode and play MP3 audio files stored on CDs.

Networked audio players: Players that connect via (WiFi) network to receive and play audio.

Common audio formats

MP3 is the dominant format, and is nearly universally supported. The main alternative formats are AAC and WMA. Unlike MP3, these formats support DRM restrictions that are often implemented into files from paid download services. Open source formats, which are completely patent-free, are available - though less widely supported. Examples include Ogg Vorbis, FLAC, and Speex.

Most players can also play uncompressed PCM in a container such as WAV or AIFF.

Controversy

Although these issues aren’t usually controversial within digital audio players, they are matters of continuing controversy and litigation, including but not limited to content distribution and protection, and digital rights management (DRM).

Lawsuit with RIAA

The Recording Industry Association of America (RIAA) filed a lawsuit with Diamond Multimedia for its Rio players, alleging that the device encouraged copying music illegally. But Diamond won a legal victory on the shoulders of the Sony Corp. v. Universal City Studios case and DAPs were legally ruled as electronic devices.

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