Encyclopedia of Computer Science and Technology

452 spreadsheetSpeech recognition begins with digitizing the speechsounds and converting them into a standard, compact representation.The analysis can be based on matching the inputsounds to one of about 200 “spectral equivalence classes”from which the representation can be created. Alternatively,algorithms can use data based on modeling how the humanvocal tract produces speech sounds, and extract key featuresthat then become the speech representation. Neuralnetworks can also be “trained” to recognize speech features(see neural network). The latter two approachesare potentially more flexible but also considerably more difficult,and tend to be used in research rather than in commercialvoice recognition systems.Whichever form of representation is used, it must thenbe matched to the characteristics of particular words orphonemes, usually with the aid of sophisticated statisticaland time-fitting techniques. The simplest systems work ona word level, which may suffice if the system is restrictedto a simple vocabulary and the user speaks slowly and distinctlyenough. Such systems usually require that the user“train” the system by speaking selected words and phrases.The user can then control the system with a set of voicecommands.Creating a system that can handle the full range of languageis much more difficult. This kind of system breaksthe language down into phonemes, its basic sound constituents(English has about 40 phonemes). The system includesa stored dictionary of phoneme sequences and the correspondingwords. However, “understanding” which wordsare being spoken is more than a matter of matching phonemesequences to a dictionary. For one thing, the sound ofthe first or last phoneme in a word can change dependingon the phoneme in an adjacent word.Once the speech has been recognized, it can be convertedto character data (see characters and strings)and treated as though the text had been entered from thekeyboard. This means, for example, that a user could dictatetext to be placed in a word processor document as wellas using voice commands to perform tasks such as formattingtext. (Special words can be used to introduce and endcommands.)Voice control and dictation have been offered commerciallyby such companies as Dragon Systems and Kurzweil.Microsoft now includes speech recognition and synthesisfacilities in the latest version of its popular office suite,Office 2007.Voice SynthesisThe other part of the speech equation is the ability to havethe computer turn character codes into spoken words. Themost primitive approach is to digitally record appropriatespoken words or phrases, which can then be replayedwhen speech is desired. Naturally, what is spoken is limitedto what is available in the recorded library, although thewords and phrases can be combined in various ways. Sincethe combinations lack the natural transitions that speakersuse, the result sounds “mechanical.” Common applicationsinclude automated announcements in train stations or inprompts for voicemail systems.To produce a synthesizer that can “speak” any naturallanguage text, the system must have a dictionary that givesthe phonemes found in each word. The 40 or so differentphonemes can then be digitally recorded and the systemwould then identify the phonemes in each word and playthem to create speech. While this solves the limited vocabularyproblem, the synthesized speech is rather unnaturaland hard to understand. This is because, as noted earlier,the way phonemes are sounded changes under the influenceof adjacent phonemes, and these nuances are lackingin a simple phoneme playback.More sophisticated voice synthesis systems record naturalspeech and identify all the possible combinations of halfof a phoneme and half of an adjacent phoneme. That way thepossible transition sounds are also recorded, and the resultingspeech sounds considerably more natural. The drawbackis that more memory and processing power are required, butthese commodities are becoming increasingly cheaper.Speech recognition and synthesis technology has madeonly slow inroads into the computing mainstream, suchas office applications. Given the costs of hardware, software,and training, the keyboard remains more productiveand cost-effective for most applications. However, voicetechnology does have a growing number of specialty uses,including security and access systems, speech synthesis fordisabled persons who cannot see or speak, and enablingservice robots to interact with people in the environment.Speech technology has also been a long-standing topic inartificial intelligence and robotics research.Further ReadingBrown, Robert. “Exploring New Speech Recognition and SynthesisAPIs in Windows Vista.” MSDN Magazine. Available online.URL: http://msdn.microsoft.com/msdnmag/issues/06/01/speechinWindowsVista/. Accessed August 22, 2007.Holmes, John, and Wendy Holmes. Speech Synthesis and Recognition.2nd ed. Boca Raton, Fla.: CRC Press, 2001.Huang, Xuedong, Alex Acero, and Hsiao-Wuen Hon. Spoken LanguageProcessing: A Guide to Theory, Algorithm, and SystemDevelopment. Upper Saddle River, N.J.: Prentice Hall, 2001.Jurafsky, Daniel, and James H. Martin. Speech and Language Processing:An Introduction to Natural Language Processing, ComputationalLinguistics and Speech Recognition. Upper SaddleRiver, N.J.: Prentice Hall, 2000.Speech Technology (Google Directory). Available online. URL:http://www.google.com/Top/Computers/Speech_Technology/.Accessed August 22, 2007.Speech Technology Research, Development, and Deployment(Carnegie Mellon University). Available online. URL: http://www.speech.cs.cmu.edu/. Accessed August 22, 2007.spreadsheetWith the possible exception of word processing, no personalcomputer application caught the imagination of thebusiness world as quickly as did the spreadsheet, whichfirst appeared as Daniel Bricklin’s VisiCalc in 1979. Visi-Calc quickly became the “killer app”—the application thatcould justify corporate purchases of Apple II computers.When the IBM PC began to dominate the office computingindustry in the mid-1980s, it had a new spreadsheet, Lotus1-2-3. By the end of the decade, however, Microsoft’s Excel