In general, "Speech synthesizers" are text-to-speech systems used with computers. It can be a card that is inserted into the computer, a box attached to the computer by a cable, or software that works with the computer's sound card. Speech synthesizers are programmed to include all the phonemes and grammatical rules of a language, allowing words to be pronounced correctly although names and compound words can cause problems because they often contain unusual spellings and letter combinations. Some synthetic speech sounds robotic; however, more and more new products sound almost human. Software synthesizers are routinely included with the purchase of a screen reader.

Answered by Karthick AR , an ibibo Master, at 12:16 PM on November 24, 2008

Speech synthesis is the computer-generated simulation of human speech. It is used to translate written information into aural information where it is more convenient, especially for mobile applications such as voice-enabled e-mail and unified messaging . It is also used to assist the vision-impaired so that, for example, the contents of a display screen can be automatically read aloud to a blind user. Speech synthesis is the counterpart of speech or voice recognition . The earliest speech synthesis effort was in 1779 when Russian Professor Christian Kratzenstein created an apparatus based on the human vocal tract to demonstrate the physiological differences involved in the production of five long vowel sounds. The first fully functional voice synthesizer, Homer Dudley's VODER (Voice Operating Demonstrator), was shown at the 1939 World's Fair. The VODER was based on Bell Laboratories' vocoder (voice coder) research of the mid-thirties.

Speech prosthesis is computer-generated speech for people with physical disabilities that make it difficult to speak intelligibly. Much of the research in this area integrates text and speech generation both, since the disabilities that create problems with speech frequently make text entry difficult as well. Given the speed and fluidity of human conversation, the challenge of speech prosthesis is to circumvent these difficulties. The main research goal is to create a prosthetic system that will as closely as possible resemble natural speech, with the least required input from the user. Speech prosthesis systems also make it possible for visually-impaired people to use computers.

Multimodal speech synthesis (sometimes referred to as audio-visual speech synthesis) incorporates an animated face synchronized to complement the synthesized speech. The same difficulties underlying an individual's speech impairment often hinder their ability to communicate through facial expressions. Although synthesized speech is increasingly life-like, it may be quite some time before it approaches the capacity for nuances of natural speech. Multimodal systems incorporate a means of adding non-verbal cues to speech (such as head-shaking, smiling, and winking, for example) to make the user's meaning as clear as possible.

Answered by Nishu%27s , an ibibo Master, at 10:44 PM on November 23, 2008

Speech synthesis is the artificial production of human speech. A computer system used for this purpose is called a speech synthesizer, and can be implemented in software or hardware. A text-to-speech (TTS) system converts normal language text into speech; other systems render symbolic linguistic representations like phonetic transcriptions into speech.[1]

Synthesized speech can be created by concatenating pieces of recorded speech that are stored in a database. Systems differ in the size of the stored speech units; a system that stores phones or diphones provides the largest output range, but may lack clarity. For specific usage domains, the storage of entire words or sentences allows for high-quality output. Alternatively, a synthesizer can incorporate a model of the vocal tract and other human voice characteristics to create a completely "synthetic" voice output.[2]

The quality of a speech synthesizer is judged by its similarity to the human voice, and by its ability to be understood. An intelligible text-to-speech program allows people with visual impairments or reading disabilities to listen to written works on a home computer. Many computer operating systems have included speech synthesizers since the early 1980s.

A text-to-speech system (or "engine") is composed of four parts: a front-end and a back-end. The front-end has two major tasks. First, it converts raw text containing symbols like numbers and abbreviations into the equivalent of written-out words. This process is often called text normalization, pre-processing, or tokenization. The front-end then assigns phonetic transcriptions to each word, and divides and marks the text into prosodic units, like phrases, clauses, and sentences. The process of assigning phonetic transcriptions to words is called text-to-phoneme or grapheme-to-phoneme conversion.[3] Phonetic transcriptions and prosody information together make up the symbolic linguistic representation that is output by the front-end. The back-end—often referred to as the synthesizer—then converts the symbolic linguistic representation into sound.

Answered by Nagendra , an ibibo Master, at 8:35 AM on November 23, 2008

The speech synthesizer is device that is used to translate text characters into sounds that approximate the sound of human speech. Depending on the level of sophistication of the individual device, the sounds produced may be somewhat stilted and artificial sounding, or sound very much like the voice of a real person. The concept of speech synthesis has been around for centuries, but only in recent decades has the process become available to the general public.

There are examples of attempts to artificially produce human speech patterns that go back to the 11th century. The earliest attempts often used materials to replicate human vocal cords and apply various types of stimulation in order to produce sounds. Over time, designs made it possible to produce sounds that mimicked the pronunciation of vowels. By the latter part of the 18th century, a few designs were also able to produce sounds that closely resembled consonants.

The real progress with the modern speech synthesizer began in the 1930’s. Bell Laboratories produced a synthesizer that was dubbed the vocoder. Data was entered with the use of a keyboard, analyzed by the system, and the appropriate sounds emitted to form words. While the intonation and inflection of the words were somewhat primitive, the device did produce clearly intelligible words. A refined version of this device, the voder, was introduced to the public at the 1939 World’s Fair.

By the 1950’s, work on a speech synthesizer that would use visual images as well as entered text produced partially successful results. At the same time, advances in technology began to refine the sound quality. By the time that automated voice communications became more prevalent in the 1970’s, there were several speech synthesizers that were capable of producing sounds that were very close to human speech patterns. In a short time, the devices were being used to produce such products as pre-recorded messages on answering machines and reading products for persons who were visually impaired.

The advent of the personal computer also opened the door to further refinements for the speech synthesizer. By including the device on a home computer system, persons with reading disabilities or limited vision are able to enjoy using a variety of computer programs. Today, the voice quality on most models of the speech synthesizer is far removed from the robotic sounds produced by devices created in the early 20th century. Many versions today are capable of producing voice patterns that are almost indistinguishable from human speech.
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Answered by Point , an ibibo Master, at 8:08 AM on November 23, 2008