Polycom is an American multinational corporation that develops video and content collaboration and communication technology. The firm employs approximately 3,800 employees and had revenues of approximately $1.4 billion in 2013. It is the largest pure-play collaboration company in its industry, in July 2016, it was announced that the company was being taken private by private equity firm Siris Capital Group. Polycom was co-founded in 1990 by Brian L Hinman and Jeffrey Rodman, in 2016, telecommunications executive Mary McDowell was named as its chief executive officer. Polycoms development occurred both by internal means, and by the acquisition of other companies, on April 15,2016, Polycom announced that rival Mitel Networks would purchase them, for $1.96 billion. Mitel, a company based in Ottawa, pays a lower tax rate. In July 2016, the Mitel deal was scrapped, and instead the company took an offer from NY City-based private equity firm Siris Capital Group. Polycoms first products to market were audio conferencing speakerphones, soon after, the company added content sharing, video conferencing, and video network and bridging products.
Polycom entered the video conferencing market in 1998, Polycom introduced the ViewStation product line which included models with embedded multipoint capabilities, content sharing capabilities, and support for the emerging H.323 IP network protocol. In 2000, Polycom introduced a desktop video conferencing appliance called ViaVideo. The compact device was essentially a web cam with inboard processing capabilities, as computer processing power increased, Polycom transitioned the desktop solution to a software-based client called Polycom PVX. In February 2001, Polycom acquired Accord Networks, which offered the MGC-100 line, in October 2001, it acquired PictureTel. In 2006, Polycom introduced its first high definition video conferencing system, in February 2007, the firm introduced a new bridge platform called RMX2000 designed to support high definition and telepresence applications. In 2008, Polycom delivered the Polycom Converged Management Application a video network, the CMA includes an application for broadscale desktop video called CMA Desktop.
Later that year, the introduced the Distributed Media Application 7000. Toward the end of 2008, Polycom announced its plans to higher resolution – 1080p and 720p at 60 frames per second – across its visual communication product line. The first SoundStation conference phone shipped in 1992, the original device was followed by versions offering extended performance. The SoundStation first shipped internationally in 1993, followed by other products, the SoundStation was superseded by the SoundStation 2 in 2004 when AT&T discontinued its DSP16A processor on which the original machine was based
Silence is the lack of audible sound or presence of sounds of very low intensity. By analogy, the silence can refer to any absence of communication or hearing, including in media other than speech. Silence is used as communication, in reference to nonverbal communication. Silence refers to no sounds uttered by anybody in a room or area, Silence is an important factor in many cultural spectacles, as in rituals. In discourse analysis, speakers use brief absences of speech to mark the boundaries of prosodic units, Silence in speech can be due to hesitation, self-correction—or a deliberate slowing of speech to clarify or aid the processing of ideas. Longer pauses in language occur in interactive roles, reactive tokens, according to cultural norms, silence can be positive or negative. Music inherently depends on silence in some form or another to distinguish other periods of sound and allow dynamics, for example, most music scores feature rests denoting periods of silence. In addition, silence in music can be seen as a time for contemplation to reflect on the piece, the audience feels the effects of the notes previous and can reflect on that moment intentionally.
Silence does not hinder musical excellence but can enhance the sounds of instruments, in his book Sound and Silence the composer John Paynter says that the dramatic effect of silence has long been appreciated by composers. The silence is intended to communicate a momentary sensation of terror, another example of a dramatic silence comes in the rest full of tension at the climactic ending of the Hallelujah Chorus in Handel’s Messiah, Musical silences may convey humour. Haydn’s Quartet in E flat, Op, the result is an inevitable giggle—the same giggle that overtakes a prestidigitator’s audience when it realizes that it has been ‘had’. Barry Cooper writes extensively of Beethoven’s many uses of silence for contemplation, for dramatic effect, the substitution of such a note by a whole-bar rest therefore gives the effect of a suppressed sound, as if one were about to speak but refrains at the last moment. The suppressed sound is repeated in bar 4, and developed in bars 7 and 8. Grove writes of the irregularity of rhythm in the sixth bar of this movement.
Some of the most effective musical silences are very short, lasting barely a fraction of a second, in the spirited and energetic finale of his Symphony No. 2, Brahms uses silences at points to powerfully disrupt the rhythmic momentum that has been building. During the 20th century, composers explored further the potential of silence in their music. The contemplative concluding bars of Anton Webern’s Symphony and Stravinsky’s Les Noces make telling, John Paynter vividly conveys how silence contributes to the titanic impact of the third section of Messiaen’s orchestral work Et exspecto resurrectionem mortuorum, Woodwinds jump and shriek
United States Patent and Trademark Office
The USPTO is unique among federal agencies because it operates solely on fees collected by its users, and not on taxpayer dollars. The USPTO is based in Alexandria, after a 2005 move from the Crystal City area of neighboring Arlington, the head of the USPTO is Michelle K. Lee. She took up her new role on January 13,2014, on March 13, she formally took office as Director after being nominated by President Barack Obama and confirmed by the U. S. Senate. She formerly served as the Director of the USPTOs Silicon Valley satellite office, the USPTO cooperates with the European Patent Office and the Japan Patent Office as one of the Trilateral Patent Offices. The USPTO mission is to maintain a permanent, interdisciplinary historical record of all U. S. patent applications in order to fulfill objectives outlined in the United States Constitution. The legal basis for the United States patent system is Article 1, Section 8, an additional building in Arlington, was opened in 2009. The USPTO was expected by 2014 to open its first ever satellite offices in Detroit, Denver, the first satellite office opened in Detroit on July 13,2012.
In 2013, due to the sequestration, the satellite office for Silicon Valley. However and infrastructure updates continued after the sequestration, and the Silicon Valley location is due to open in San Jose City Hall in mid-2015. As of September 30,2009, the end of the U. S. governments fiscal year, of those,6,242 were patent examiners and 388 were trademark examining attorneys, the rest are support staff. They are generally newly graduated scientists and engineers, recruited from universities around the nation. They hold degrees in scientific disciplines, but who do not necessarily hold law degrees. Unlike patent examiners, trademark examiners must be licensed attorneys, all examiners work under a strict, count-based production system. For every application, counts are earned by composing and mailing a first office action on the merits, the Patent Operations of the office is divided into nine different technology centers that deal with various arts. Prior to 2012, decisions of patent examiners may be appealed to the Board of Patent Appeals and Interferences, the United States Supreme Court may ultimately decide on a patent case.
Similarly, decisions of trademark examiners may be appealed to the Trademark Trial and Appeal Board, with subsequent appeals directed to the Federal Circuit, under the America Invents Act, the BPAI was converted to the Patent Trial and Appeal Board or PTAB. In recent years, the USPTO has seen increasing delays between when a patent application is filed and when it issues, to address its workload challenges, the USPTO has undertaken an aggressive program of hiring and recruitment. The USPTO hired 1,193 new patent examiners in Fiscal Year 2006,1,215 new examiners in fiscal 2007, in 2006, USPTO instituted a new training program for patent examiners called the Patent Training Academy
Through its numerous acquired subsidiaries, such as OpenDNS, WebEx, and Jasper, Cisco specializes into specific tech markets, such as Internet of Things, domain security, and energy management. Cisco is the largest networking company in the world, the stock was added to the Dow Jones Industrial Average on June 8,2009, and is included in the S&P500 Index, the Russell 1000 Index, NASDAQ-100 Index and the Russell 1000 Growth Stock Index. By the time the company went public in 1990, when it was listed on the NASDAQ, Cisco was the most valuable company in the world by 2000, with a more than $500 billion market capitalization. Despite founding Cisco in 1984, along with Kirk Lougheed, continued to work at Stanford on Ciscos first product and it consisted of exact replicas of Stanfords Blue Box router and a stolen copy of the Universitys multiple-protocol router software. The software was written some years earlier at Stanford medical school by research engineer William Yeager. Bosack and Lougheed adapted it into what became the foundation for Cisco IOS, in 1987, Stanford licensed the router software and two computer boards to Cisco.
In addition to Bosack and Lougheed, Greg Satz, a programmer, and Richard Troiano, the companys first CEO was Bill Graves, who held the position from 1987 to 1988. In 1988, John Morgridge was appointed CEO, the name Cisco was derived from the city name San Francisco, which is why the companys engineers insisted on using the lower case cisco in its early years. The logo is intended to depict the two towers of the Golden Gate Bridge, on February 16,1990, Cisco Systems went public and was listed on the NASDAQ stock exchange. On August 28,1990, Lerner was fired, upon hearing the news, her husband Bosack resigned in protest. The couple walked away from Cisco with $170 million, 70% of which was committed to their own charity, although Cisco was not the first company to develop and sell dedicated network nodes, it was one of the first to sell commercially successful routers supporting multiple network protocols. Classical, CPU-based architecture of early Cisco devices coupled with flexibility of operating system IOS allowed for keeping up with evolving technology needs by means of frequent software upgrades, some popular models of that time managed to stay in production for almost a decade virtually unchanged—a rarity in high-tech industry.
This philosophy dominated the companys product lines throughout the 1990s, in 1995, John Morgridge was succeeded by John Chambers. The phenomenal growth of the Internet in mid-to-late 1990s quickly changed the telecom landspe, as the Internet Protocol became widely adopted, the importance of multi-protocol routing declined. In late March 2000, at the height of the bubble, Cisco became the most valuable company in the world. In July 2014, with a cap of about US$129 billion. One of them, Juniper Networks, shipped their first product in 1999, Cisco answered the challenge with homegrown ASICs and fast processing cards for GSR routers and Catalyst 6500 switches. In 2004, Cisco started migration to new high-end hardware CRS-1, as part of a massive rebranding campaign in 2006, Cisco Systems adopted the shortened name Cisco and created The Human Network advertising campaign
Internet Assigned Numbers Authority
Following ICANNs transition to a global multistakeholder governance model, the IANA functions were transferred to Public Technical Identifiers, an affiliate of ICANN. In addition, five regional Internet registries delegate number resources to their customers, local Internet registries, Internet service providers, a local Internet registry is an organization that assigns parts of its allocation from a regional Internet registry to other customers. Most local Internet registries are Internet service providers, IANA is broadly responsible for the allocation of globally unique names and numbers that are used in Internet protocols that are published as Request for Comments documents. These documents describe methods, research, or innovations applicable to the working of the Internet, IANA maintains a close liaison with the Internet Engineering Task Force and RFC Editorial team in fulfilling this function. IANA is responsible for assignment of Internet numbers which are numerical identifier assigned to an Internet resource or used in the protocols of the Internet Protocol Suite.
Examples include IP addresses and autonomous system numbers, IANA delegates allocations of IP address blocks to regional Internet registries. Each RIR allocates addresses for a different area of the world, collectively the RIRs have created the Number Resource Organization formed as a body to represent their collective interests and ensure that policy statements are coordinated globally. The RIRs divide their allocated address pools into smaller blocks and delegate them to Internet service providers, since the exhaustion of the Internet Protocol Version 4 address space, no further IPv4 address space is allocated by IANA. IANA administers the data in the root nameservers, which form the top of the hierarchical Domain name system tree and this task involves liaising with top-level domain operators, the root nameserver operators, and ICANNs policy making apparatus. IANA administers many parameters of IETF protocols, examples include the names of uniform resource identifier schemes and character encodings recommended for use on the Internet.
This task is performed under the oversight of the Internet Architecture Board, on March 26,1972, Vint Cerf and Jon Postel at UCLA called for establishing a socket number catalog in RFC322. Network administrators were asked to submit a note or place a call, describing the function. This catalog was published as RFC433 in December 1972. In it Postel first proposed a registry of assignments of port numbers to network services, calling himself the czar of socket numbers. The first reference to the name IANA in the RFC series is in RFC1083, published in December,1988 by Postel at USC-ISI, there was widespread dissatisfaction with this concentration of power in one company, and people looked to IANA for a solution. Postel wrote up a draft on IANA and the creation of new top level domains and he was trying to institutionalize IANA. In retrospect, this would have been valuable, since he died about two years later. Jon Postel managed the IANA function from its inception on the ARPANET until his death in October 1998, by his almost 30 years of selfless service, Postel created his de facto authority to manage key parts of the Internet infrastructure
Code-excited linear prediction
Code-excited linear prediction is a speech coding algorithm originally proposed by M. R. Schroeder and B. S. Atal in 1985. At the time, it provided better quality than existing low bit-rate algorithms, such as residual-excited linear prediction. Along with its variants, such as algebraic CELP, relaxed CELP, low-delay CELP and vector sum excited linear prediction and it is used in MPEG-4 Audio speech coding. CELP is commonly used as a term for a class of algorithms. Applying vector quantization The original algorithm as simulated in 1983 by Schroeder, since then, more efficient ways of implementing the codebooks and improvements in computing capabilities have made it possible to run the algorithm in embedded devices, such as mobile phones. Before exploring the complex encoding process of CELP we introduce the decoder here, figure 1 describes a generic CELP decoder. The fixed codebook is a vector quantization dictionary that is hard-coded into the codec and this codebook can be algebraic or be stored explicitly.
The entries in the adaptive codebook consist of delayed versions of the excitation and this makes it possible to efficiently code periodic signals, such as voiced sounds. The filter that shapes the excitation has a model of the form 1 / A. An all-pole filter is used because it is a representation of the human vocal tract. The main principle behind CELP is called Analysis-by-Synthesis and means that the encoding is performed by perceptually optimizing the decoded signal in a closed loop. In theory, the best CELP stream would be produced by trying all possible bit combinations and this is obviously not possible in practice for two reasons, the required complexity is beyond any currently available hardware and the “best sounding” selection criterion implies a human listener. For example, the ear is tolerant to noise in parts of the spectrum that are louder. Thats why instead of minimizing the simple quadratic error, CELP minimizes the error for the perceptually weighted domain, the weighting filter W is typically derived from the LPC filter by the use of bandwidth expansion, W = A A where γ1 > γ2.
This article is based on a paper presented at Linux. Conf. Au Some parts based on the Speex codec manual reference implementations of CELP 1016A and LPC 10e. Linear Predictive Coding Introduction to CELP Coding Speech Processing, Theory of LPC Analysis and Synthesis B. S. Atal, The History of Linear Prediction, IEEE Signal Processing Magazine, vol
Multimedia is content that uses a combination of different content forms such as text, images, animations and interactive content. Multimedia contrasts with media that use only rudimentary computer displays such as text-only or traditional forms of printed or hand-produced material, Multimedia devices are electronic media devices used to store and experience multimedia content. Multimedia is distinguished from mixed media in art, for example. The term rich media is synonymous with interactive multimedia, the term multimedia was coined by singer and artist Bob Goldstein to promote the July 1966 opening of his LightWorks at LOursin show at Southampton, Long Island. Goldstein was perhaps aware of an American artist named Dick Higgins, two years later, in 1968, the term multimedia was re-appropriated to describe the work of a political consultant, David Sawyer, the husband of Iris Sawyer—one of Goldsteins producers at LOursin. In the intervening forty years, the word has taken on different meanings, in the late 1970s, the term referred to presentations consisting of multi-projector slide shows timed to an audio track.
However, by the 1990s multimedia took on its current meaning, in the 1993 first edition of Multimedia, Making It Work, Tay Vaughan declared Multimedia is any combination of text, graphic art, sound and video that is delivered by computer. When you allow the user – the viewer of the project – to control what, when you provide a structure of linked elements through which the user can navigate, interactive multimedia becomes hypermedia. The German language society Gesellschaft für deutsche Sprache recognized the words significance, the institute summed up its rationale by stating has become a central word in the wonderful new media world. In common usage, multimedia refers to an electronically delivered combination of media including video, still images, much of the content on the web today falls within this definition as understood by millions. That era saw a boost in the production of educational multimedia CD-ROMs, the term video, if not used exclusively to describe motion photography, is ambiguous in multimedia terminology.
Video is often used to describe the format, delivery format. Multiple forms of content are often not considered modern forms of presentation such as audio or video. Likewise, single forms of content with single methods of information processing are often called multimedia. Performing arts may be considered multimedia considering that performers and props are multiple forms of content and media. Multimedia presentations may be viewed by person on stage, transmitted, a broadcast may be a live or recorded multimedia presentation. Broadcasts and recordings can be analog or digital electronic media technology. Digital online multimedia may be downloaded or streamed, streaming multimedia may be live or on-demand
In signal processing, data compression, source coding, or bit-rate reduction involves encoding information using fewer bits than the original representation. Compression can be 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, the process of reducing the size of a data file is referred to as data compression. In the context of data transmission, it is called coding in opposition to channel coding. Compression is useful because it reduces resources required to store and transmit data, computational resources are consumed in the compression process and, usually, in the reversal of the process. Data compression is subject to a space–time complexity trade-off, Lossless data compression algorithms usually exploit statistical redundancy to represent data without losing any information, so that the process is reversible.
Lossless compression is possible because most real-world data exhibits statistical redundancy, for example, an image may have areas of color that do not change over several pixels, instead of coding red pixel, red pixel. The data may be encoded as 279 red pixels and this is a basic example of run-length encoding, there are many schemes to reduce file size by eliminating redundancy. The Lempel–Ziv compression methods are among the most popular algorithms for lossless storage, DEFLATE is a variation on LZ optimized for decompression speed and compression ratio, but compression can be slow. DEFLATE is used in PKZIP, and PNG, LZW is used in GIF images. LZ methods use a table-based compression model where table entries are substituted for repeated strings of data, for most LZ methods, this table is generated dynamically from earlier data in the input. The table itself is often Huffman encoded, current LZ-based coding schemes that perform well are Brotli and LZX. LZX is used in Microsofts CAB format, the best modern lossless compressors use probabilistic models, such as prediction by partial matching.
The Burrows–Wheeler transform can be viewed as a form of statistical modelling. The basic task of grammar-based codes is constructing a context-free grammar deriving a single string, sequitur and Re-Pair are practical grammar compression algorithms for which software is publicly available. In a further refinement of the use of probabilistic modelling. Arithmetic coding is a more modern coding technique that uses the mathematical calculations of a machine to produce a string of encoded bits from a series of input data symbols
Fax, sometimes called telecopying or telefax, is the telephonic transmission of scanned printed material, normally to a telephone number connected to a printer or other output device. The receiving fax machine interprets the tones and reconstructs the image, early systems used direct conversions of image darkness to audio tone in a continuous or analog manner. Since the 1980s, most machines modulate the audio frequencies using a digital representation of the page which is compressed to quickly transmit areas which are all-white or all-black. Scottish inventor Alexander Bain worked on chemical mechanical fax type devices and he received British patent 9745 on May 27,1843 for his Electric Printing Telegraph. Frederick Bakewell made several improvements on Bains design and demonstrated a telefax machine, the Pantelegraph was invented by the Italian physicist Giovanni Caselli. He introduced the first commercial service between Paris and Lyon in 1865, some 11 years before the invention of the telephone.
In 1880, English inventor Shelford Bidwell constructed the scanning phototelegraph that was the first telefax machine to scan any two-dimensional original, photographs had been sent over the radio using this process. The Western Union Deskfax fax machine, announced in 1948, was a machine that fit comfortably on a desktop. As a designer for the Radio Corporation of America, in 1924, Richard H. Ranger invented the wireless photoradiogram, or transoceanic radio facsimile, the forerunner of today’s fax machines. A photograph of President Calvin Coolidge sent from New York to London on November 29,1924 became the first photo picture reproduced by transoceanic radio facsimile, commercial use of Ranger’s product began two years later. Also in 1924, Herbert E. Ives of AT&T Corporation transmitted and reconstructed the first color facsimile, around 1952 or so, Finch Facsimile, a highly developed machine, was described in detail in a book, it was never manufactured in quantity. By the late 1940s, radiofax receivers were sufficiently miniaturized to be fitted beneath the dashboard of Western Unions Telecar telegram delivery vehicles, in the 1960s, the United States Army transmitted the first photograph via satellite facsimile to Puerto Rico from the Deal Test Site using the Courier satellite.
Radio fax is still in limited use today for transmitting weather charts, in 1964, Xerox Corporation introduced what many consider to be the first commercialized version of the modern fax machine, under the name or Long Distance Xerography. This model was superseded two years with a unit that would set the standard for fax machines for years to come. Up until this point facsimile machines were expensive and hard to operate. In 1966, Xerox released the Magnafax Telecopiers, a smaller and this unit was far easier to operate and could be connected to any standard telephone line. This machine was capable of transmitting a letter-sized document in about six minutes, the first sub-minute, digital fax machine was developed by Dacom, which built on digital data compression technology originally developed at Lockheed for satellite communication. By the late 1970s, many companies around the world, entered the fax market, very shortly after a new wave of more compact and efficient fax machines would hit the market
Conexant Systems, Inc. is an American-based software developer and fabless semiconductor company that provides products for voice and audio processing and modems. The company began as a division of Rockwell International, before being spun off as a public company, Conexant itself spun off several business units, creating independent public companies which included Skyworks Solutions and Mindspeed Technologies. In 1996, Rockwell International Corporation incorporated its semiconductor division as Rockwell Semiconductor Systems, on January 4,1999, Rockwell spun off Conexant Systems, Inc. as a public company. It was listed on the NASDAQ under symbol CNXT on January 4,1999, at that time, Conexant became the worlds largest, standalone communications-IC company. Dwight W. Decker was its first chief officer and Chairman of its Board of Directors. The company was based in Newport Beach, California, in the early 2000s, Conexant spun off several standalone technology businesses to create public companies.
In March 2002, Conexant entered into a joint venture agreement with The Carlyle Group to share ownership of its fabrication plant. In June 2003, Conexant spun off its Internet infrastructure business to create the publicly held company Mindspeed Technologies Inc, Mindspeed would eventually be acquired by Lowell, MA-based M/A-COM Technology Solutions. In 2004, Conexant merged with Red Bank, New Jersey semiconductor company GlobespanVirata, GlobespanVirata’s name was changed to Conexant, Inc. In September 2008, Jazz was sold to Israel-based Tower Semiconductor Ltd, in August 2009, Conexant sold its broadband access product line to Fremont, CA semiconductor company Ikanos Communications. Bankruptcy Court for the District of Delaware, as part of the bankruptcy agreement, the company agreed on a restructuring plan with owners and its sole secured lender, QP SFM Capital Holdings Ltd. The reorganized company emerged from bankruptcy in July 2013, since 2013, Conexants silicon and software solutions for voice processing have been instrumental in the CE industrys proliferation of voice-enabled devices.
Based on the Conexant AudioSmart™ CX20921 Voice Input Processor, the dual microphone board was designed to reduce time-to-market for new third-party voice-enabled Alexa devices, Conexant has two main product families, the AudioSmart brand of audio processors and the ImagingSmart brand of image processors and modems. AD Converters - Conexants analog to digital converters are used for far-field voice/speech capture applications and they convert analog signals to digital in order to enhance the signal before transmitting it to third party speech recognition products. The technology is used in voice-enabled consumer products, a low power version with a standby mode and a fast wake up mode is used for battery powered devices. Codecs - Conexants codecs encode and decode digital signals, to allow transmission, encryption, the codecs are used to improve audio signals in tablets and PCs, and for consumer audio applications such as conferencing, streaming media and editing. USB & I2S DSP codecs - Conexants DSP codecs have USB and integrated interchip sound interfaces to connect to devices such as headsets.
VoiceSpeech processors - Conexants VoiceSpeech line of system-on-chip speech processors add voice command capabilities to smart TVs, far-field voice pre-processing algorithms and 24-bit analog-to-digital conversion prevent a noisy television itself from interfering with a users commands
Dual-tone multi-frequency signaling
DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963. DTMF is standardized by ITU-T Recommendation Q.23 and it is known in the UK as MF4. The Touch-Tone system using a telephone keypad gradually replaced the use of dial and has become the industry standard for landline. Other multi-frequency systems are used for internal signaling within the telephone network, prior to the development of DTMF, telephone numbers were dialed by users with a loop-disconnect signaling, more commonly known as pulse dialing in the U. S. The exchange equipment responds to the dial pulses either directly by operating relays, the physical distance for which this type of dialing was possible was restricted by electrical distortions and was only possible on direct metallic links between end points of a line. Placing calls over longer distances required either operator assistance or provision of special subscriber trunk dialing equipment, operators used an earlier type of multi-frequency signaling.
Multi-frequency signaling is a group of signaling methods that use a mixture of two pure tone sounds, various MF signaling protocols were devised by the Bell System and CCITT. This semi-automated signaling and switching proved successful in both speed and cost effectiveness, the DTMF system uses a set of eight audio frequencies transmitted in pairs to represent 16 signals, represented by the ten digits, the letters A to D, and the symbols # and *. AT&T described the product as a method for pushbutton signaling from customer stations using the transmission path. DTMF was known throughout the Bell System by the trademark Touch-Tone, the term was first used by AT&T in commerce on July 5,1960 and was introduced to the public on November 18,1963, when the first push-button telephone was made available to the public. It was a trademark by AT&T from September 4,1962 to March 13,1984. It is standardized by ITU-T Recommendation Q.23, in the UK, it is known as MF4. Other vendors of compatible telephone equipment called the Touch-Tone feature tone dialing or DTMF, terrestrial television stations used DTMF tones to control remote transmitters.
The engineers had envisioned telephones being used to access computers, and they consulted with companies to determine the requirements. This led to the addition of the sign and asterisk or star keys as well as a group of keys for menu selection. Public payphones that accept credit cards use these codes to send the information from the magnetic strip. The AUTOVON telephone system of the United States Armed Forces used these signals to assert certain privilege, precedence is still a feature of military telephone networks, but using number combinations. For example, entering 93 before a number is a priority call, present-day uses of the A, B, C and D signals on telephone networks are few, and are exclusive to network control
A vocoder is a category of voice codec that analyzes and synthesizes the human voice signal for audio data compression, voice encryption, voice transformation, etc. The decoder applies these control signals to corresponding filters for re-synthesis, since these control signals change only slowly compared to the original speech waveform, the bandwidth required to transmit speech can be reduced. This allows more speech channels to share a single communication channel, by encrypting the control signals, voice transmission can be secured against interception. Its primary use in fashion is for secure radio communication. The advantage of this method of encryption is that none of the signal is sent. The receiving unit needs to be set up in the same filter configuration to re-synthesize a version of the signal spectrum. The vocoder has used extensively as an electronic musical instrument. The decoder portion of the vocoder, called a voder, can be used independently for speech synthesis, the human voice consists of sounds generated by the opening and closing of the glottis by the vocal cords, which produces a periodic waveform with many harmonics.
This basic sound is filtered by the nose and throat to produce differences in harmonic content in a controlled way. There is another set of sounds, known as the unvoiced and plosive sounds, the vocoder examines speech by measuring how its spectral characteristics change over time. This results in a series of signals representing these modified frequencies at any time as the user speaks. In simple terms, the signal is split into a number of frequency bands, the vocoder dramatically reduces the amount of information needed to store speech, from a complete recording to a series of numbers. Information about the frequency of the original voice signal is discarded. It is this aspect of the vocoding process that has made it useful in creating special voice effects in popular music. Analog vocoders typically analyze an incoming signal by splitting the signal into a number of tuned frequency bands or ranges, a modulator and carrier signal are sent through a series of these tuned bandpass filters. In the example of a robot voice, the modulator is a microphone.
There are usually between eight and 20 bands, the amplitude of the modulator for each of the individual analysis bands generates a voltage that is used to control amplifiers for each of the corresponding carrier bands. The result is that components of the modulating signal are mapped onto the carrier signal as discrete amplitude changes in each of the frequency bands