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VSELP
Vector sum excited linear prediction (VSELP) is a speech coding method used in several cellular standards. The VSELP algorithm is an analysis-by-synthesis coding technique and belongs to the class of speech coding algorithms known as CELP (Code Excited Linear Prediction).ETSIEN 300 969 - Half rate speech transcoding (GSM 06.20 version 8.0.1 Release 1999) Retrieved on 2009-07-11 Variations of this codec have been used in several 2G cellular telephony standards, including IS-54, IS-136 (D-AMPS), GSM (Half Rate speech) and iDEN. It was also used in the first version of RealAudio for audio over the Internet. The IS-54 VSELP standard was published by the Telecommunications Industry Association in 1989. D-AMPS (IS-54 and IS-136) VSELP specifies an encoding of each 20 ms of speech into 159-bit frames, thus achieving a raw data rate of 7.95 kbit/s. In an actual TDMA cell phone, the vocoder output is packaged with error correction and signaling information, resulting in an over-the-air da ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IS-54
IS-54 and IS-136 are second-generation ( 2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System (AMPS). It was once prevalent throughout the Americas, particularly in the United States and Canada since the first commercial network was deployed in 1993. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies. This system is most often referred to as TDMA. That name is based on the abbreviation for time-division multiple access, a common multiple access technique which is used in most 2G standards, including GSM, as well as in IS-54 and IS-136. D-AMPS competed against GSM and systems based on code-division multiple access (CDMA). D-AMPS uses existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IS-136
IS-54 and IS-136 are second-generation ( 2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System (AMPS). It was once prevalent throughout the Americas, particularly in the United States and Canada since the first commercial network was deployed in 1993. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies. This system is most often referred to as TDMA. That name is based on the abbreviation for time-division multiple access, a common multiple access technique which is used in most 2G standards, including GSM, as well as in IS-54 and IS-136. D-AMPS competed against GSM and systems based on code-division multiple access (CDMA). D-AMPS uses existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Half Rate
Half Rate (HR or GSM-HR or GSM 06.20) is a speech coding system for GSM, developed in the early 1990s. Since the codec, operating at 5.6 kbit/s, requires half the bandwidth of the Full Rate codec, network capacity for voice traffic is doubled, at the expense of audio quality. The sampling rate is 8 kHz with resolution 13 bit, frame length 160 samples (20 ms) and subframe length 40 samples (5 ms). GSM Half Rate is specified in ETSI EN 300 969 (GSM 06.20), and uses a form of the VSELP algorithm. Previous specification was in ETSI ETS 300 581–2, which first edition was published in December 1995. Retrieved on 2009-07-11 For some Nokia phones one can configure the use of this codec: * To a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RealAudio
RealAudio, or also spelled as Real Audio is a proprietary audio format developed by RealNetworks and first released in April 1995. It uses a variety of audio codecs, ranging from low-bitrate formats that can be used over dialup modems, to high-fidelity formats for music. It can also be used as a streaming audio format, that is played at the same time as it is downloaded. In the past, many internet radio stations used RealAudio to stream their programming over the internet in real time. In recent years, however, the format has become less common and has given way to more popular audio formats. RealAudio was heavily used by the BBC websites until 2009, though it was discontinued due to its declining use. BBC World Service, the last of the BBC websites to use RealAudio, discontinued its use in March 2011. File extensions RealAudio files were originally identified by a filename extension of .ra (for Real Audio). In 1997, RealNetworks also began offering a video format called RealVideo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Speech Coding
Speech coding is an application of data compression of digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting modeled parameters in a compact bitstream. Some applications of speech coding are mobile telephony and voice over IP (VoIP). The most widely used speech coding technique in mobile telephony is linear predictive coding (LPC), while the most widely used in VoIP applications are the LPC and modified discrete cosine transform (MDCT) techniques. The techniques employed in speech coding are similar to those used in audio data compression and audio coding where knowledge in psychoacoustics is used to transmit only data that is relevant to the human auditory system. For example, in voiceband speech coding, only information in the frequency band 400 to 3500 Hz is transmitted but the reconst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CELP
Code-excited linear prediction (CELP) is a linear predictive speech coding algorithm originally proposed by Manfred R. Schroeder and Bishnu S. Atal in 1985. At the time, it provided significantly better quality than existing low bit-rate algorithms, such as residual-excited linear prediction (RELP) and linear predictive coding (LPC) vocoders (e.g., FS-1015). Along with its variants, such as algebraic CELP, relaxed CELP, low-delay CELP and vector sum excited linear prediction, it is currently the most widely used speech coding algorithm. It is also used in MPEG-4 Audio speech coding. CELP is commonly used as a generic term for a class of algorithms and not for a particular codec. Background The CELP algorithm is based on four main ideas: * Using the source-filter model of speech production through linear prediction (LP) (see the textbook "speech coding algorithm"); * Using an adaptive and a fixed codebook as the input (excitation) of the LP model; * Performing a search in close ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Codec
A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or data stream, and hence is a type of codec. ''Endec'' is a portmanteau of encoder/decoder. A coder or encoder encodes a data stream or a signal for transmission or storage, possibly in encrypted form, and the decoder function reverses the encoding for playback or editing. Codecs are used in videoconferencing, streaming media, and video editing applications. History In the mid-20th century, a codec was a device that coded analog signals into digital form using pulse-code modulation (PCM). Later, the name was also applied to software for converting between digital signal formats, including companding functions. Examples An audio codec converts analog audio signals into digital signals for transmission or encodes them for storage. A receiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Integrated Digital Enhanced Network
Integrated Digital Enhanced Network (iDEN) is a mobile telecommunications technology, developed by Motorola, which provides its users the benefits of a trunked radio and a cellular telephone. It was called the first mobile social network by many technology industry analysts. iDEN places more users in a given spectral space, compared to analog cellular and two-way radio systems, by using speech compression and time-division multiple access (TDMA). History The iDEN project originally began as MIRS (Motorola Integrated Radio System) in early 1991. The project was a software lab experiment focused on the utilization of discontiguous spectrum for GSM wireless. GSM systems typically require 24 contiguous voice channels, but the original MIRS software platform dynamically selected fragmented channels in the radio frequency (RF) spectrum in such a way that a GSM telecom switch could commence a phone call the same as it would in the contiguous channel scenario. Operating frequencies ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies. The Internet carries a vast range of information resources and services, such as the inter-linked hypertext documents and applications of the World Wide Web (WWW), electronic mail, telephony, and file sharing. The origins of the Internet date back to the development of packet switching and research commissioned by the United States Department of Defense in the 1960s to enable time-sharing of computers. The primary precursor network, the ARPANET, initially served as a backbone for interconnection of regional academic and military networks in the 1970s to enable resource shari ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecommunications Industry Association
The Telecommunications Industry Association (TIA) is accredited by the American National Standards Institute (ANSI) to develop voluntary, consensus-based industry standards for a wide variety of Information and Communication Technologies (Information and communication technologies, ICT) products, and currently represents nearly 400 companies. TIA's Standards and Technology Department operates twelve engineering committees, which develop guidelines for private radio equipment, cellular towers, data terminals, satellites, telephone terminal equipment, accessibility, VoIP devices, structured cabling, data centers, mobile device communications, multimedia multicast, vehicular telematics, healthcare ICT, Machine to machine, machine to machine communications, and smart grid, smart utility networks. Active participants include communications equipment manufacturers, service providers, government agencies, academic institutions, and end-users are engaged in TIA's standards setting proc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Millisecond
A millisecond (from '' milli-'' and second; symbol: ms) is a unit of time in the International System of Units (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds. A unit of 10 milliseconds may be called a centisecond, and one of 100 milliseconds a decisecond, but these names are rarely used. To help compare orders of magnitude of different times, this page lists times between 10−3 seconds and 100 seconds (1 millisecond and one second). ''See also'' times of other orders of magnitude. Examples The Apollo Guidance Computer used metric units internally, with centiseconds used for time calculation and measurement. *1 millisecond (1 ms) – cycle time for frequency 1 kHz; duration of light for typical photo flash strobe; time taken for sound wave to travel about 34 cm; repetition interval of GPS C/A PN code *1 millisecond - time taken for light to travel 204.19 km in a single mode fiber optic cable for a wavelength o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vocoder
A vocoder (, a portmanteau of ''voice'' and ''encoder'') is a category of speech coding that analyzes and synthesizes the human voice signal for audio data compression, multiplexing, voice encryption or voice transformation. The vocoder was invented in 1938 by Homer Dudley at Bell Labs as a means of synthesizing human speech. This work was developed into the channel vocoder which was used as a voice codec for telecommunications for speech coding to conserve bandwidth in transmission. By encrypting the control signals, voice transmission can be secured against interception. Its primary use in this fashion is for secure radio communication. The advantage of this method of encryption is that none of the original signal is sent, only envelopes of the bandpass filters. The receiving unit needs to be set up in the same filter configuration to re-synthesize a version of the original signal spectrum. The vocoder has also been used extensively as an electronic musical instrument. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
