Ethernet is a family of computer networking technologies used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3, has since retained a good deal of backward compatibility and been refined to support higher bit rates and longer link distances. Over time, Ethernet has replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET; the original 10BASE5 Ethernet uses coaxial cable as a shared medium, while the newer Ethernet variants use twisted pair and fiber optic links in conjunction with switches. Over the course of its history, Ethernet data transfer rates have been increased from the original 2.94 megabits per second to the latest 400 gigabits per second. The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet. Systems communicating over Ethernet divide a stream of data into shorter pieces called frames; each frame contains source and destination addresses, error-checking data so that damaged frames can be detected and discarded.
As per the OSI model, Ethernet provides services up including the data link layer. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols including Wi-Fi wireless networking technology. Ethernet is used in home and industry; the Internet Protocol is carried over Ethernet and so it is considered one of the key technologies that make up the Internet. Ethernet was developed at Xerox PARC between 1973 and 1974, it was inspired by ALOHAnet. The idea was first documented in a memo that Metcalfe wrote on May 22, 1973, where he named it after the luminiferous aether once postulated to exist as an "omnipresent, completely-passive medium for the propagation of electromagnetic waves." In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, Butler Lampson as inventors. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper; that same year, Ron Crane, Bob Garner, Roy Ogus facilitated the upgrade from the original 2.94 Mbit/s protocol to the 10 Mbit/s protocol, released to the market in 1980.
Metcalfe left Xerox in June 1979 to form 3Com. He convinced Digital Equipment Corporation and Xerox to work together to promote Ethernet as a standard; as part of that process Xerox agreed to relinquish their'Ethernet' trademark. The first standard was published on September 1980 as "The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications"; this so-called DIX standard specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and a global 16-bit Ethertype-type field. Version 2 was published in November, 1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the same time and resulted in the publication of IEEE 802.3 on June 23, 1983. Ethernet competed with Token Ring and other proprietary protocols. Ethernet was able to adapt to market realities and shift to inexpensive thin coaxial cable and ubiquitous twisted pair wiring. By the end of the 1980s, Ethernet was the dominant network technology. In the process, 3Com became a major company.
3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, that year started selling adapters for PDP-11s and VAXes, as well as Multibus-based Intel and Sun Microsystems computers. This was followed by DEC's Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986, making it one of the largest computer networks in the world at that time. An Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced with drivers for DOS and Windows. By the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, Ethernet ports began to appear on some PCs and most workstations; this process was sped up with the introduction of 10BASE-T and its small modular connector, at which point Ethernet ports appeared on low-end motherboards. Since Ethernet technology has evolved to meet new bandwidth and market requirements.
In addition to computers, Ethernet is now used to interconnect appliances and other personal devices. As Industrial Ethernet it is used in industrial applications and is replacing legacy data transmission systems in the world's telecommunications networks. By 2010, the market for Ethernet equipment amounted to over $16 billion per year. In February 1980, the Institute of Electrical and Electronics Engineers started project 802 to standardize local area networks; the "DIX-group" with Gary Robinson, Phil Arst, Bob Printis submitted the so-called "Blue Book" CSMA/CD specification as a candidate for the LAN specification. In addition to CSMA/CD, Token Ring and Token Bus were considered as candidates for a LAN standard. Competing proposals and broad interest in the initiative led to strong disagreement over which technology to standardize. In December 1980, the group was split into three subgroups, standardization proceeded separately for each proposal. Delays in the standards process put at risk the market introduction of the Xerox Star workstation and 3Com's Ethernet LAN products.
With such business implications in mind, David Liddle an
Internet radio is a digital audio service transmitted via the Internet. Broadcasting on the Internet is referred to as webcasting since it is not transmitted broadly through wireless means, it can either be used as a stand-alone device running through the internet, or as a software running through a single computer. Internet radio is used to communicate and spread messages through the form of talk, it is distributed through a wireless communication network connected to a switch packet network via a disclosed source.'Internet radio involves streaming media, presenting listeners with a continuous stream of audio that cannot be paused or replayed, much like traditional broadcast media. Internet radio is distinct from podcasting, which involves downloading rather than streaming. Internet radio services offer news, sports and various genres of music—every format, available on traditional broadcast radio stations. Many Internet radio services are associated with a corresponding traditional radio station or radio network, although low start-up and ongoing costs have allowed a substantial proliferation of independent Internet-only radio stations.
The first Internet radio service was launched in 1993. As of 2017, the most popular internet radio platforms and applications in the world include TuneIn Radio, iHeartRadio,and Sirius XM. Internet radio services are accessible from anywhere in the world with a suitable internet connection available; this has made internet radio suited to and popular among expatriate listeners. Some major networks like TuneIn Radio, Pandora Radio, iHeartRadio and Citadel Broadcasting in the United States, Chrysalis in the United Kingdom, restrict listening to in-country due to music licensing and advertising issues. Internet radio is suited to listeners with special interests, allowing users to pick from a multitude of different stations and genres less represented on traditional radio. Internet radio is listened to on a standard home PC or similar device, through an embedded player program located on the respective station's website. In recent years, dedicated devices that resemble and offer the listener a similar experience to a traditional radio receiver have arrived on the market.
Streaming technology is used to distribute Internet radio using a lossy audio codec. Streaming audio formats include MP3, Ogg Vorbis, Windows Media Audio, RealAudio, HE-AAC. Audio data is continuously transmitted serially over the local network or internet in TCP or UDP packets reassembled at the receiver and played a second or two later; the delay is called lag, is introduced at several stages of digital audio broadcasting. A local tuner simulation program includes all the online radios that can be heard in the air in the city. In 2003, revenue from online streaming music radio was US$49 million. By 2006, that figure rose to US$500 million. A February 21, 2007 "survey of 3,000 Americans released by consultancy Bridge Ratings & Research" found that "s much as 19% of U. S. consumers 12 and older listen to Web-based radio stations." In other words, there were "some 57 million weekly listeners of Internet radio programs. More people listen to online radio than to satellite radio, high-definition radio, podcasts, or cell-phone-based radio combined."
An April 2008 Arbitron survey showed that, in the US, more than one in seven persons aged 25–54 years old listen to online radio each week. In 2008, 13 percent of the American population listened to the radio online, compared to 11 percent in 2007. Internet radio functionality is built into many dedicated Internet radio devices, which give an FM like receiver user experience. In the fourth quarter of 2012, TuneIn Radio, iHeart Radio, other subscription-based and free Internet radio services accounted for nearly one quarter of the average weekly music listening time among consumers between the ages of 13 and 35, an increase from a share of 17 percent the previous year; as Internet-radio listening rose among the 13-to-35 age group, listening to AM/FM radio, which now accounts for 24 percent of music-listening time, declined 2 percentage points. In the 36-and-older age group, by contrast, Internet radio accounted for just 13 percent of music listening, while AM/FM radio dominated listening methods with a 41 percent share.
47% of all Americans ages 12 and older—an estimated 124 million people—said they have listened to online radio in the last month, while 36% have listened in the last week. These figures are up from 45% and 33% in 2013; the average amount of time spent listening increased from 11 hours, 56 minutes per week in 2013 to 13 hours 19 minutes in 2014. As might be expected, usage numbers are much higher for teens and younger adults, with 75% of Americans ages 12–24 listening to online radio in the last month, compared to 50% of Americans ages 25–54 and 21% of Americans 55+; the weekly figures for the same age groups were 37 % and 13 %, respectively. In 2015, it was recorded that 53% of Americans, or 143 million people, ages 12 and up listen to internet radio; some stations, such as Primordial Radio, use Internet radio as a platform as opposed to other means such as FM or DAB, as it gives greater freedom to broadcast as they see fit, without being subject to regulatory bodies such as Ofcom in the UK.
For example, Ofcom has strict rules about presenters e
An RCA connector, sometimes called a phono connector or Cinch connector, is a type of electrical connector used to carry audio and video signals. The name RCA derives from the Radio Corporation of America, which introduced the design by the early 1940s for internal connection of the pickup to the chassis in home radio-phonograph consoles, it was a low-cost, simple design, intended only for mating and disconnection when servicing the console. Refinement came with designs, although they remained compatible. RCA connectors began to replace the older quarter-inch phone connectors for many other applications in the consumer audio world when component high-fidelity systems started becoming popular in the 1950s. However, quarter-inch phone connectors are still common in professional audio, while miniature phone connectors predominated in personal stereo systems; the connection's plug is called an RCA plug or phono plug, for "phonograph." The name "phono plug" is sometimes confused with a "phone plug" which may refer to a quarter-inch "phone plug" – Tip/Sleeve or Tip/Ring/Sleeve connector – or to a 4P4C connector used for a telephone.
The word phono in phono connector is an abbreviation of the word phonograph, because this connector was created to allow the connection of a phonograph turntable to a radio receiver, using the radio as an amplifier. This setup was present in most radios manufactured in the 1930s onward by the Radio Corporation of America, who marketed a special turntable for 45 RPM records, the model 9JY. A phono input is a set of input jacks RCA jacks, located on the rear panel of a preamp, mixer or amplifier on early radio sets, to which a phonograph or turntable is attached. Modern styli and phono cartridges give a low level output signal of the order of a few millivolts which the circuitry amplifies and equalizes. Phonograph recordings are made with high frequencies boosted and the low frequencies attenuated: during playback the frequency response changes are reversed; this reduces background noise, including clicks or pops, conserves the amount of physical space needed for each groove, by reducing the size of the larger low-frequency undulations.
This is accomplished in the amplifier with a phono input that incorporates standardized RIAA equalization circuitry. Through at least the 1980s, the phono input was available on consumer stereo equipment—even some larger boomboxes had them. By the 2000s only sophisticated and expensive stereo receivers retained the phono input, since most users were expected to use digital music formats such as CD or satellite radio; some newer low-cost turntables include built-in amplifiers to produce line-level outputs. Nearly all DJ mixers have two or more phono inputs, together with two or more one-volt line inputs that use RCA connectors; this "phono input" designed for the millivolt signal from an unamplified turntable should not be confused with the modern standard one-volt line input and output that uses RCA connectors and is found on video cameras and similar modern equipment. In the most normal use, cables have a standard plug on each end, consisting of a central male connector, surrounded by a ring.
The ring is segmented to provide spring gripping pressure when mated. Devices mount the socket; the ring is larger in diameter and longer than the ring on the plug, allowing the plug's ring to fit over it. The jack has a small area between the outer and inner rings, filled with an insulator plastic; the connector was used for audio signals. As with many other connectors, the RCA has been adopted for other uses than intended, including as a DC power connector, an RF connector, as a connector for loudspeaker cables, its use as a connector for composite video signals is common, but provides poor impedance matching. RCA connectors and cable are commonly used to carry S/PDIF-formatted digital audio, with plugs colored orange to differentiate them from other typical connections. Connections are made by pushing the cable's plug into the female jack on the device; the signal-carrying pin protrudes from the plug, comes into contact with the socket before the grounded rings meet, resulting in loud hum or buzz if the audio components do not share a common ground and are powered while making connections.
Continuous noise can occur if the plug falls out of the jack, breaking the ground connection but not the signal. Some variants of the plug cheaper versions give poor grip and contact between the ground sheaths due to their lack of spring action, they are color-coded, yellow for composite video, red for the right audio channel, white or black for the left channel of stereo audio. This trio of jacks can be found on the back of all audio and video equipment. One or more sets are found on TV sets to facilitate connection of camcorders, other portable video sources and video game consoles. Although nearly all connectors, including analog and S/PDIF audio as well as composite and component video, can use identical 75 Ω cables, sales of special-purpose cables for each use have proliferated. Varying cable quality means that a cheap line-level audio cable might not transfer component video. For digital audio, as long as a connection is made using the cabl
SHOUTcast DNAS is cross-platform proprietary software for streaming media over the Internet. The software, developed by Nullsoft, is available free of charge, it allows digital audio content in MP3 or High-Efficiency Advanced Audio Coding format, to be broadcast to and from media player software, enabling the creation of Internet radio "stations". The most common use of SHOUTcast is for listening to Internet audio broadcasts; some traditional radio stations use SHOUTcast to extend their presence onto the Web. SHOUTcast Radio is a related website. Created in 1998, SHOUTcast's streaming protocol uses metadata tags and responses that all start with ICY, which stands for "I Can Yell." Nullsoft was purchased by AOL on June 1, 1999. On January 14, 2014, AOL sold Nullsoft to Belgian online radio aggregator Radionomy; the SHOUTcast software uses a client–server model, with each component communicating via a network protocol that intermingles audio or video data with metadata such as song titles and the station name.
It uses HTTP as a transport protocol. Although multicast was planned, it was never developed. SHOUTcast servers and clients are available for FreeBSD, macOS, Microsoft Windows, Solaris. Client-only versions exist for Android, BlackBerry OS, iOS, Palm OS and webOS, PlayStation Portable, Windows Mobile, Symbian S60 and UIQ, Nintendo DS, Wii; the output format is supported by multiple clients, including Nullsoft's own Winamp as well as Amarok, foobar2000, iTunes, Totem, XMMS, Zinf. If the client does not support the SHOUTcast protocol the SHOUTcast server sends the stream without the metadata thus allowing it to be heard/viewed in clients like Windows Media Player. SHOUTcast servers are linked to by means of playlist files, which are small text files that contain the URL of the SHOUTcast server; when that URL is visited in a Web browser which identifies itself as Mozilla-compatible, the server will return a generated SHOUTcast server info/status page, rather than streaming audio. A feature of SHOUTcast servers is the ability to optionally publish server information, including the current number of listeners, in a directory of stations that AOL maintains on the SHOUTcast website.
Site visitors can pick a station to listen to and download a playlist file for use in their own SHOUTcast-capable media player. In September 2008, AOL redesigned the SHOUTcast website, the same since 2000. In 2010, SHOUTcast again redesigned it with more of an AOL look; as part of the redesign, the directory and services were rebranded as "SHOUTcast Radio", rather than "SHOUTcast Streaming Technology." The redesign included a functional option to view the site and directory with the old layout. At the time VideoLAN said that AOL's license for use of the SHOUTcast Radio servers would “ us to integrate the spyware and adware based Shoutcast Radio Toolbar inside your browser.” and thus prevents open source software from using the SHOUTcast Radio servers. SHOUTcast said in 2011 that up to 900,000 concurrent listeners could be seen on public streams during peak hours; the audience on private streams is unknown. The maximum and minimum number of listeners fluctuates during a day, with three times as many listeners during peak hours as at low use times.
As of May 2014 SHOUTcast Radio included over 50,000 stations. During the early days of eSports for video games, SHOUTcast was used by some to stream play-by-play commentary on eSport matches; this led to the term "shoutcaster" which remains in use today to describe eSports commentators if they are not using the plugin. Sources: Icecast List of Internet radio stations List of streaming media systems Nullsoft Streaming Video Edcast Official website
Streaming media is multimedia, received by and presented to an end-user while being delivered by a provider. The verb "to stream" refers to the process of obtaining media in this manner. A client end-user can use their media player to start playing digital video or digital audio content before the entire file has been transmitted. Distinguishing delivery method from the media distributed applies to telecommunications networks, as most of the delivery systems are either inherently streaming or inherently non-streaming. For example, in the 1930s, elevator music was among the earliest popular music available as streaming media; the term "streaming media" can apply to media other than video and audio, such as live closed captioning, ticker tape, real-time text, which are all considered "streaming text". Live streaming is the delivery of Internet content in real-time much as live television broadcasts content over the airwaves via a television signal. Live internet streaming requires a form of source media, an encoder to digitize the content, a media publisher, a content delivery network to distribute and deliver the content.
Live streaming does not need to be recorded at the origination point, although it is. There are challenges with streaming content on the Internet. If the user does not have enough bandwidth in their Internet connection, they may experience stops, lags, or slow buffering of the content; some users may not be able to stream certain content due to not having compatible computer or software systems. Some popular streaming services include the video sharing website YouTube and Mixer, which live stream the playing of video games. Netflix and Amazon Video stream movies and TV shows, Spotify, Apple Music and TIDAL stream music. In the early 1920s, George O. Squier was granted patents for a system for the transmission and distribution of signals over electrical lines, the technical basis for what became Muzak, a technology streaming continuous music to commercial customers without the use of radio. Attempts to display media on computers date back to the earliest days of computing in the mid-20th century.
However, little progress was made for several decades due to the high cost and limited capabilities of computer hardware. From the late 1980s through the 1990s, consumer-grade personal computers became powerful enough to display various media; the primary technical issues related to streaming were having enough CPU power bus bandwidth to support the required data rates, creating low-latency interrupt paths in the operating system to prevent buffer underrun, enabling skip-free streaming of the content. However, computer networks were still limited in the mid-1990s, audio and video media were delivered over non-streaming channels, such as by downloading a digital file from a remote server and saving it to a local drive on the end user's computer or storing it as a digital file and playing it back from CD-ROMs. In 1991 the first commercial Ethernet Switch was introduced, which enabled more powerful computer networks leading to the first streaming video solutions used by schools and corporations such as expanding Bloomberg Television worldwide.
In the mid 1990s the World Wide Web was established, but streaming audio would not be practical until years later. During the late 1990s and early 2000s, users had increased access to computer networks the Internet. During the early 2000s, users had access to increased network bandwidth in the "last mile"; these technological improvements facilitated the streaming of audio and video content to computer users in their homes and workplaces. There was an increasing use of standard protocols and formats, such as TCP/IP, HTTP, HTML as the Internet became commercialized, which led to an infusion of investment into the sector; the band Severe Tire Damage was the first group to perform live on the Internet. On June 24, 1993, the band was playing a gig at Xerox PARC while elsewhere in the building, scientists were discussing new technology for broadcasting on the Internet using multicasting; as proof of PARC's technology, the band's performance was broadcast and could be seen live in Australia and elsewhere.
In a March 2017 interview, band member Russ Haines stated that the band had used "half of the total bandwidth of the internet" to stream the performance, a 152-by-76 pixel video, updated eight to twelve times per second, with audio quality, "at best, a bad telephone connection". Microsoft Research developed a Microsoft TV application, compiled under MS Windows Studio Suite and tested in conjunction with Connectix QuickCam. RealNetworks was a pioneer in the streaming media markets, when it broadcast a baseball game between the New York Yankees and the Seattle Mariners over the Internet in 1995; the first symphonic concert on the Internet took place at the Paramount Theater in Seattle, Washington on November 10, 1995. The concert was a collaboration between The Seattle Symphony and various guest musicians such as Slash, Matt Cameron, Barrett Martin; when Word Magazine launched in 1995, they featured the first-ever streaming soundtracks on the Internet. Metro
Windows Media Player
Windows Media Player is a media player and media library application developed by Microsoft, used for playing audio and viewing images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices. Editions of Windows Media Player were released for classic Mac OS, Mac OS X and Solaris but development of these has since been discontinued. In addition to being a media player, Windows Media Player includes the ability to rip music from and copy music to compact discs, burn recordable discs in Audio CD format or as data discs with playlists such as an MP3 CD, synchronize content with a digital audio player or other mobile devices, enable users to purchase or rent music from a number of online music stores. Windows Media Player replaced an earlier application called Media Player, adding features beyond simple video or audio playback. Windows Media Player 11 is available for Windows XP and included in Windows Vista and Windows Server 2008.
The default file formats are Windows Media Video, Windows Media Audio, Advanced Systems Format, its own XML based playlist format called Windows Playlist. The player is able to utilize a digital rights management service in the form of Windows Media DRM. Windows Media Player 12 is the most recent version of Windows Media Player, it was released on October 22, 2009 along with Windows 7 and has not been made available for previous versions of Windows or has it been updated since for Windows 8, Windows 8.1 and Windows 10. These versions of Windows instead use Groove Music and Microsoft Movies & TV as the default playback applications for most media. Windows RT does not run Windows Media Player; the first version of Windows Media Player appeared in 1991, when Windows 3.0 with Multimedia Extensions was released. Called Media Player, this component was included with "Multimedia PC"-compatible machines but not available for retail sale, it was capable of playing.mmm animation files, could be extended to support other formats.
It used MCI to handle media files. Being a component of Windows, Media Player shows the same version number as that of the version Windows with which it was included. Microsoft continually produced new programs to play media files. In November of the following year, Video for Windows was introduced with the ability to play digital video files in an AVI container format, with codec support for RLE and Video1, support for playing uncompressed files. Indeo 3.2 was added in a release. Video for Windows was first available as a free add-on to Windows 3.1, integrated into Windows 95 and Windows NT 4.0. In 1995, Microsoft released ActiveMovie with DirectX Media SDK. ActiveMovie incorporates a new way of dealing with media files, adds support for streaming media. In 1996, ActiveMovie was renamed DirectShow. However, Media Player continued to come with Windows until Windows XP, in which it was renamed Windows Media Player v5.1. In 1999, Windows Media Player's versioning broke away from that of Windows itself.
Windows Media Player 6.4 came as an out-of-band update for Windows 95, Windows 98 and Windows NT 4.0 that co-existed with Media Player and became a built-in component of Windows 2000, Windows ME and Windows XP with an mplayer2.exe stub allowing to use this built-in instead of newer versions. Windows Media Player 7.0 and its successors came in the same fashion, replacing each other but leaving Media Player and Windows Media Player 6.4 intact. Windows XP is the only operating system to have three different versions of Windows Media Player side by side. All versions branded. Windows Media Player version 7 was a large revamp, with a new user interface and increased functionality. Windows Vista, dropped older versions of Windows Media Player in favor of v11. Beginning with Windows Vista, Windows Media Player supports the Media Foundation framework besides DirectShow. Windows Media Player 12 was released with Windows 7, it added new features. With Windows 8, the player did not receive an upgrade. On April 16, 2012, Microsoft announced that Windows Media Player would not be included in Windows RT, the line of Windows designed to run on ARM based devices.
Windows Media Player supports playback of audio and pictures, along with fast forward, file markers and variable playback speed. It supports streaming playback with multicast streams and progressive downloads. Items in a playlist can be skipped over temporarily at playback time without removing them from the playlist. Full keyboard-based operation is possible in the player. Windows Media Player supports full media management, via the integrated media library introduced first in version 7, which offers cataloguing and searching of media and viewing media metadata. Media can be arranged according to album, genre, date et al. Windows Media Player 9 Series introduced Quick Access Panel to browse and navigate the entire library through a menu; the Quick Access Panel was added to the mini mode in version 10 but was removed in version 11. WMP 9 Series introduced ratings and Auto Ratings. Windows Media Player 10 introduced support for aggregating pictures, Recorded TV shows, other media into the library.
Digital audio is sound, recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is encoded as numerical samples in continuous sequence. For example, in CD audio, samples are taken 44100 times per second each with 16 bit sample depth. Digital audio is the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s, it replaced analog audio technology in many areas of audio engineering and telecommunications in the 1990s and 2000s. In a digital audio system, an analog electrical signal representing the sound is converted with an analog-to-digital converter into a digital signal using pulse-code modulation; this digital signal can be recorded, edited and copied using computers, audio playback machines, other digital tools. When the sound engineer wishes to listen to the recording on headphones or loudspeakers, a digital-to-analog converter performs the reverse process, converting a digital signal back into an analog signal, sent through an audio power amplifier and to a loudspeaker.
Digital audio systems may include compression, storage and transmission components. Conversion to a digital format allows convenient manipulation, storage and retrieval of an audio signal. Unlike analog audio, in which making copies of a recording results in generation loss and degradation of signal quality, digital audio allows an infinite number of copies to be made without any degradation of signal quality. Digital audio technologies are used in the recording, mass-production, distribution of sound, including recordings of songs, instrumental pieces, sound effects, other sounds. Modern online music distribution depends on digital recording and data compression; the availability of music as data files, rather than as physical objects, has reduced the costs of distribution. Before digital audio, the music industry distributed and sold music by selling physical copies in the form of records and cassette tapes. With digital-audio and online distribution systems such as iTunes, companies sell digital sound files to consumers, which the consumer receives over the Internet.
An analog audio system converts physical waveforms of sound into electrical representations of those waveforms by use of a transducer, such as a microphone. The sounds are stored on an analog medium such as magnetic tape, or transmitted through an analog medium such as a telephone line or radio; the process is reversed for reproduction: the electrical audio signal is amplified and converted back into physical waveforms via a loudspeaker. Analog audio retains its fundamental wave-like characteristics throughout its storage, transformation and amplification. Analog audio signals are susceptible to noise and distortion, due to the innate characteristics of electronic circuits and associated devices. Disturbances in a digital system do not result in error unless the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturb the sequence of symbols, it is therefore possible to have an error-free digital audio system in which no noise or distortion is introduced between conversion to digital format, conversion back to analog.
A digital audio signal may optionally be encoded for correction of any errors that might occur in the storage or transmission of the signal. This technique, known as channel coding, is essential for broadcast or recorded digital systems to maintain bit accuracy. Eight-to-fourteen modulation is a channel code used in the audio compact disc. A digital audio system starts with an ADC; the ADC converts at a known bit resolution. CD audio, for example, has a sampling rate of 44.1 kHz, has 16-bit resolution for each stereo channel. Analog signals that have not been bandlimited must be passed through an anti-aliasing filter before conversion, to prevent the aliasing distortion, caused by audio signals with frequencies higher than the Nyquist frequency. A digital audio signal may be transmitted. Digital audio can be stored on a CD, a digital audio player, a hard drive, a USB flash drive, or any other digital data storage device; the digital signal may be altered through digital signal processing, where it may be filtered or have effects applied.
Sample-rate conversion including upsampling and downsampling may be used to conform signals that have been encoded with a different sampling rate to a common sampling rate prior to processing. Audio data compression techniques, such as MP3, Advanced Audio Coding, Ogg Vorbis, or FLAC, are employed to reduce the file size. Digital audio can be carried over digital audio interfaces such as AES3 or MADI. Digital audio can be carried over a network using audio over Ethernet, audio over IP or other streaming media standards and systems. For playback, digital audio must be converted back to an analog signal with a DAC which may use oversampling. Pulse-code modulation was invented by British scientist Alec Reeves in 1937 and was used in telecommunications applications long before its first use in commercial broadcast and recording. Commercial digital recording was pioneered in Japan by NHK and Nippon Columbia and their Denon brand, in the 1960s; the first commercial digital recordings were released in 1971.
The BBC began to experiment with digital audio in the 1960s. By the early 1970s, it had developed a 2-channel recorder