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Perceptual Audio Coder
Perceptual Audio Coder (PAC) is a lossy audio compression algorithm. It is used by Sirius Satellite Radio for their digital audio radio service. Development The original version of PAC developed by James Johnston and Anibal Ferreira at AT&T's Bell Labs has a flexible format and bitrate. It provides efficient compression of high-quality audio over a variety of formats from 16 kbit/s for a monophonic channel to 1024 kbit/s for a 5.1 format with four or six auxiliary audio channels, and provisions for an ancillary (fixed rate) and auxiliary (variable rate) side data channel. For stereo audio signals, it is claimed that it provides near-CD quality at about 56-64 kbit/s, with transparent coding at bit rates approaching 128 kbit/s. Over the years PAC has evolved considerably. A known software implementation of this codec is CelestialTech's AudioLib. Later, it was considerably improved and renamed to ePAC (enhanced Perceptual Audio Coder) by Lucent, available in the AudioVeda mu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lossy Audio Compression
In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy. No information is lost in lossless compression. Lossy compression reduces bits by removing unnecessary or less important information. Typically, a device that performs data compression is referred to as an encoder, and one that performs the reversal of the process (decompression) as a decoder. The process of reducing the size of a data file is often referred to as data compression. In the context of data transmission, it is called source coding; encoding done at the source of the data before it is stored or transmitted. Source coding should not be confused with channel coding, for error detection and correction or line coding, the means for mapping data onto a signal. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sirius Satellite Radio
Sirius Satellite Radio was a satellite radio (SDARS) and online radio service operating in North America, owned by Sirius XM Holdings. Headquartered in New York City, with smaller studios in Los Angeles and Memphis, Sirius was officially launched on July 1, 2002. It now provides 69 streams (channels) of music and 65 streams of sports, news, and entertainment to its subscribers. Music streams on Sirius carry a wide variety of genres broadcasting 24 hours daily, commercial-free, and uncensored. A subset of Sirius music channels is included as part of the Dish Network satellite television service. Sirius channels are identified by Nielsen Audio with the label "SR" (e.g. "SR120", "SR9", "SR17"). Its business model is to provide pay-for-service radio, analogous to the business model for premium cable television. Music channels are presented without advertising, while its talk channels, such as Howard Stern's Howard 100 and Howard 101 and Jason Ellis' Faction talk 103, carry co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Audio Radio Service
Digital audio radio service (Spectrum management) refers to any type of digital radio program service. In the United States it is the official FCC term for digital radio services. The most popular type of DARS in the U.S. and Canada is SDARS: Satellite Digital Audio Radio Service, used by Sirius Satellite Radio and XM Satellite Radio. XM and Sirius both operate in the 2.3-GHz S band, from 2320 to 2345 MHz. Increasing the spectrum available for more services would be difficult, since unlike C-band and Ku band services, which allow over 200 locations for satellites, S-band satellites must be spaced far apart, with current technology. Existing vehicle antennas would not allow reception of two different stations on the same frequency, though new technology, requiring a new kind of receiver, might be possible. WorldSpace also operated a DARS network outside the United States and Canada with a footprint covering Europe, Asia, the Middle East and Africa. It used the L-band. Spectrum Re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBiquity
iBiquity Digital Corporation is a company formed by the merger of USA Digital Radio and Lucent Digital Radio. Based in Columbia, Maryland, with additional offices in Basking Ridge, New Jersey, and Auburn Hills, Michigan, iBiquity is a privately held intellectual properties company with investors in the technology, broadcasting, manufacturing, media, and financial industries. About IBOC can operate on both AM band and FM band broadcasts either in a digital-only mode, or in a "hybrid" digital+analog mode. The stations can split the digital bandwidth to carry multiple audio program streams (called HD2 or HD3 multicast channels) as well as show on-screen text data such as song title and artist, traffic and weather information. Nearly 2,000 stations in the US broadcast with this system. The technology is marketed under the trademark HD Radio. It is the only technology approved by the Federal Communications Commission for digital AM and FM broadcasting in the United States. Due in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HD-Radio
HD Radio (HDR) is a trademark for an in-band on-channel (IBOC) digital radio broadcast technology. It generally simulcasts an existing analog radio station in digital format with less noise and with additional text information. HD Radio is used primarily by AM and FM radio stations in the United States, Canada, and Mexico, with a few implementations outside North America. The term "on channel" is a misnomer because the system actually broadcasts on the ordinarily unused channels adjacent to an existing radio station's allocation. This leaves the original analog signal intact, allowing enabled receivers to switch between digital and analog as required. In most FM implementations, from 96 to 128 kbps of capacity is available. High-fidelity audio requires only 48 kbps so there is ample capacity for additional channels, which HD Radio refers to as "multicasting". HD Radio is licensed so that the simulcast of the main channel is royalty-free. The company makes its money ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBOC
In-band on-channel (IBOC) is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency. The name refers to the new digital signals being broadcast in the same AM or FM band (in-band), and associated with an existing radio channel (on-channel). By utilizing additional digital subcarriers or sidebands, digital information is "multiplexed" on existing signals, thus avoiding re-allocation of the broadcast bands. IBOC relies on unused areas of the existing spectrum to send its signals. This is particularly useful in North America style FM, where channels are widely spaced at 200 kHz but use only about 50 kHz of that bandwidth for the audio signal. In most countries, FM channel spacing may be as close as 100 kHz, and on AM it is only 10 kHz. While these all offer some room for additional digital broadcasts, most attention on IBOC is in the FM band in North American systems; in Europe and many other co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Radio
Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services. Types In digital broadcasting systems, the analog audio signal is digitized, compressed using an audio coding format such as AAC+ ( MDCT) or MP2, and transmitted using a digital modulation scheme. The aim is to increase the number of radio programs in a given spectrum, to improve the audio quality, to eliminate fading problems in mobile environments, to allow additional datacasting services, and to decrease the transmission power or the number of transmitters required to cover a region. However, analog radio (AM and FM) is still more popular and listening to radio over IP (Internet Protocol) is growing in popularity. In 2012 four digital wireless radio systems are recognized by the International Telecommunication Union: the two European systems Digital Audio Broadca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency Modulation
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation, i.e. the difference between the frequency of the carrier and its center frequency, has a functional relation to the modulating signal amplitude. Digital data can be encoded and transmitted with a type of frequency modulation known as frequency-shift keying (FSK), in which the instantaneous frequency of the carrier is shifted among a set of frequencies. The frequencies may represent digits, such as '0' and '1'. FSK is widely used in computer modems, such as fax modems, telephone caller ID systems, garage door openers, and other low-frequency transmissions. Radioteletype also uses FSK. Frequency modulatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amplitude Modulation
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to that of the message signal, such as an audio signal. This technique contrasts with angle modulation, in which either the frequency of the carrier wave is varied, as in frequency modulation, or its phase, as in phase modulation. AM was the earliest modulation method used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century beginning with Roberto Landell de Moura and Reginald Fessenden's radiotelephone experiments in 1900. This original form of AM is sometimes called double-sideband amplitude modulation (DSBAM), because the standard method produces sidebands on either side of the carrier frequency. Single-sideband modulation uses bandpass filters to eliminate one of the sidebands ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HE-AAC
High-Efficiency Advanced Audio Coding (HE-AAC) is an audio coding format for lossy data compression of digital audio defined as an MPEG-4 Audio profile in ISO/IEC 14496–3. It is an extension of Low Complexity AAC (AAC-LC) optimized for low- bitrate applications such as streaming audio. The usage profile HE-AAC v1 uses spectral band replication (SBR) to enhance the modified discrete cosine transform (MDCT) compression efficiency in the frequency domain. The usage profile HE-AAC v2 couples SBR with Parametric Stereo (PS) to further enhance the compression efficiency of stereo signals. HE-AAC is used in digital radio standards like HD Radio, DAB+ and Digital Radio Mondiale. History The progenitor of HE-AAC was developed by Coding Technologies by combining MPEG-2 AAC-LC with a proprietary mechanism for spectral band replication (SBR), to be used by XM Radio for their satellite radio service. Subsequently, Coding Technologies submitted their SBR mechanism to MPEG as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
