For a number of years, computers have been able to communicate with users, after a fashion by imitating human speech. How often have you dialed a phone number only to hear, “We are Sorry: the number you are trying to reach 555-202 is no longer in service”. Voice output systems, the hardware and software responsible for such messages, convert stored digital data into spoken messages. Computerized voice output systems operate extensively at airline terminals to broadcast information about flight departures and arrivals.

In the security business they quote the prices of stocks and bonds, in supermarkets, they announce description and prices of items that pass over the scanner; in electronic mail systems they greet users and tell them about any waiting electronic mail. There are two types of voice output systems first type digitizes voice messages, stores them electronically and then converts back to voice messages when the user triggers a playback command-sort of the digital version of the traditional tape recorder. The second type of system produces synthetic speech by storing digital patterns of word sounds and then creating sentences extemporaneously. As a result these, devices perform best in creating short messages-a telephone number, stock price and so on.