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How digital audio player works
How digital audio player works
A digital audio player, shortened to DAP, is a consumer electronic device that stores, organizes and plays digital audio files. In contrast, analog audio players play music from cassette tapes, or records. Portable devices that also play video and text are referred to as portable media players. Often digital audio players are sold as MP3 players, even if they support other file formats.
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 64 GB. Because they are solid state and do not have moving parts they require less battery power, are less likely to skip during playback, and may be more resilient to hazards such as dropping or fragmentation than hard disk-based players. There are USB flash drives available that include basic MP3 playback capabilities.
• 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 500 GB. At typical encoding rates, this means that tens of thousands of songs can be stored on one player. The disadvantage with these units is that a hard drive is inherently more fragile than solid-state storage, thus more care is required to not drop or otherwise mishandle these units.
• MP3 CD/DVD players: Portable CD players that can decode and play MP3 audio files stored on CDs. Such players are typically much less expensive than either the hard drive or flash-based players. Also, the blank CD-R media is very inexpensive, typically costing less than US$.15 per disk. In addition, these devices have the added bonus of being able to play standard "Red book" audio CDs. A disadvantage is that due to the mechanical nature of these devices, they are even more fragile than the hard drive based players, and thus more susceptible to skipping or other misreads of the file during playback if mishandled. The better quality units attempt to mitigate this by providing a solid-state buffer in which the first several seconds of music is read into before playback begins. Also, a CD can typically hold only around 700 megabytes of data, thus a large library will require multiple disks to contain. However, some of the more expensive, higher-end units are also capable of reading and playing back files contained on larger capacity DVD disks as well, including the ability to playback and display video content, such as movies. More recently, portable Blu-ray players hit the market, and also portable DVD players with USB and memory card slots have come along.
• Networked audio players: Players that connect via (WiFi) network to receive and play audio. These types of units typically do not have any local storage of their own and must rely on a server, typically a personal computer also on the same network, to provide the audio files for playback.
• USB host/memory card audio players: Players that rely on USB flash drives or other memory cards to read data.
Recording
Many players have a built-in electret microphone which allows recording. Usually recording quality is poor, suitable for speech but not music.
There are also professional-quality recorders suitable for high-quality music recording with external microphones, at prices starting at a few hundred dollars.
Radio
Some DAPs have FM radio tuners built in. Many also have an option to change the band from the usual 87.5 - 108.0 MHz to the Japanese band of 76.0 - 90.0 MHz.
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 the compressed file into an analogue sound signal.
Most DAPs are powered by rechargeable batteries, some of which are not user-replaceable. They have a 3.5 mm stereo jack; music can be listened to with earbuds or headphones, or played via an external amplifier and speakers. Some devices also contain internal speakers, through which music can be listened to, although these built-in speakers are typically of very low quality.
Nearly all DAPs consists of some kind of display screen, although there are exceptions, such as the iPod Shuffle, and a set of controls with which the user can browse through the library of music contained in the device, select a track, and play it back. The display, if the unit even has one, can be anything from a simple one or two line monochrome LCD display, similar to what are found on typical pocket calculators, to large, high-resolution, full-color displays capable of displaying photographs or viewing video content on. The controls can range anywhere from the simple buttons as are found on most typical CD players, such as for skipping through tracks or stopping/starting playback to full touch-screen controls, such as that found on the iPod Touch or the Zune HD. One of the more common methods of control is some type of the scroll wheel with associated buttons. This method of control was first introduced with the Apple iPod and many other manufacturers have created variants of this control scheme for their respective devices.
Content is placed on DAPs typically through a process called "syncing", by connecting the device to a personal computer, typically via USB, and running any special software that is often provided with the DAP on a CD-ROM included with the device, or downloaded from the manufacturer's website. Some devices simply appear as an additional disk drive on the host computer, to which music files are simply copied like any other type of file. Other devices, most notably the Apple iPod or Microsoft Zune, requires the use of special management software, such as iTunes or Zune Software, respectively. The music, or other content such as TV episodes or movies, is added to the software to create a "library". The library is then "synced" to the DAP via the software. The software typically provides options for managing situations when the library is too large to fit on the device being synced to. Such options include allowing manual syncing, in that the user can manually "drag-n-drop" the desired tracks to the device, or allow for the creation of playlists. In addition to the USB connection, some of the more advanced units are now starting to allow syncing through a wireless connection, such as via WiFi or Bluetooth.
Content can also be obtained and placed on some DAPs, such as the iPod Touch or Zune HD by allowing access to a "store" or "marketplace", most notably the iTunes Store or Zune Marketplace, from which content, such as music and video, and even games, can be purchased and downloaded directly to the device.
Common audio formats
Most audio formats use lossy compression, to produce as small as possible a file compatible with the desired sound quality. There is a trade-off between size and sound quality of lossily compressed files; most formats allow different combinations—e.g., MP3 files may use between 32 (worst) and 320 (best) kilobits per second. Different lossy formats may give files of different sizes for the same perceived quality.
The formats supported by a particular DAP depend upon its firmware; sometimes a firmware update adds more formats. To listen to a file on a player, it must be in a supported format; format conversion on a computer is usually possible, but with loss of quality.
MP3 is the dominant format, and is almost universally supported. It is a proprietary format; manufacturers must pay a small royalty to be allowed to support it.
The main proprietary alternative formats are AAC and WMA. Unlike MP3, these formats support DRM restrictions that are often enforced by files from paid download services.
Free formats, which do not require manufacturers or music distributors to pay a fee, 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.
History
The immediate predecessor in the market place of the digital audio player was the portable CD player, or "portable audio device".
IXI
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. His UK patent application was not filed until 1981, patent 2115996 issued in 1985, and U.S. Patent 4,667,088 in 1987. 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.
Audio Highway Listen Up
The world's first company to announce a portable MP3 player and the attendant system for uploading MP3 audio content to a personal computer and then downloading it onto a personal MP3 player was Audio Highway. Under the direction of founder and CEO, Nathan Schulhof, Audio Highway announced its Listen Up player on September 23, 1996, won an Innovations Award for its Listen Up player and its Listen Up Personal Audio System at the Consumer Electronics Show in January 1997, and began shipping the Listen Up player in the United States in September 1997. The Listen Up player also won a People's Choice Award at the 2nd annual Internet Showcase conference, held Jan. 30, 1998. The device was not mass-produced; only about 25 units were made.
As the lead inventor on three U.S. patents (5,557,541; 5,572,442 and 5,841,979), as well as co-inventor on another U.S. patent (6,549,942), Schulhof is sometimes referred to as "the father of the MP3 player industry".
One of the chips used to create portable MP3 players was the Micronas MAS3507D ASIC MP3 Decoder chip. Several electronics DIY projects used this circuit as a software based approach would have limited battery time severely. This chip allowed the microcontroller to read data from a flash memory and feed the decoder chip, creating a low power solution.
SaeHan/Eiger MPMan
The next company on the MP3 player scene was South Korea-based SaeHan Information Systems which began selling its mass-produced “MPMan” player in April 1998. In mid-1998, the South Korean company licensed the players for North American distribution to Eiger Labs, which rebranded them as the Eiger MPMan F10 and F20. The flash-based players were available in 32 MB (about 6 songs) storage capacity.
Diamond Rio
The Rio PMP300 from Diamond Multimedia was introduced in September 1998, a few months after the MPMan, and also featured a 32 MB storage capacity. 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.
HanGo Personal Jukebox
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, with an advertised capacity of 1200 songs.
Creative NOMAD Jukebox
In 2000, Creative released the 6GB hard drive based Creative NOMAD Jukebox. The name borrowed the jukebox metaphor popularised by Remote Solution and also used by Archos. Later players in the Creative NOMAD range used microdrives rather than laptop drives.
Apple iPod
In October 2001, Apple Computer (now known as Apple Inc.) unveiled the first generation iPod, a 5 GB hard drive based DAP with a 1.8" Toshiba hard drive. With the development of a spartan user interface and a smaller form factor, the iPod was initially popular within the Macintosh community. In July 2002, Apple introduced the second generation update to the iPod. It was compatible with Windows computers through Musicmatch Jukebox. The iPod series, which grew to include flash memory-based players, has become the market leader in DAPs.
Archos Jukebox Multimedia
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.
Mobile phones
In 2001 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 mobile phones in the world have an MP3 player.
Controversy
Although these issues are not 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 in late 1998 against 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.
Risk of hearing damage
According to SCENIHR, the risk of hearing damage from digital audio players depends on both sound level and listening time. The listening habits of most users are unlikely to cause hearing loss, but some people are putting their hearing at risk, because they set the volume control very high or listen to music at high levels for many hours per day. Such listening habits may result in temporary or permanent hearing loss, tinnitus, and difficulties understanding speech in noisy environments.
Alternative methods to reduce risk
Much of the risk of hearing loss is largely associated to the fact that many use headphones with the devices, and that they consider them personal devices instead of stereo system components. However, the headphone outputs technically output line-level stereo analog audio where a TRS-to-RCA connector (though the other end is sometimes TRS) can sometimes be used for bookshelf stereo or AV receiver use as an alternative method. Car audio system use has similar benefits as users often use stereo analog AUX inputs with TRS connectors, or cassette adapters on older car audio equipment, and FM transmitters on equipment without AUX inputs or cassette deck.
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