Computers have been prattling on for a number of years now, but they have started to get downright garrulous lately. Two talking microcomputers were unveiled on the same morning recently at separate press conferences in New York City. To someone who is astounded that a computer can even beep, it was a remarkable double bill.

One of the computers, produced by Digital Equipment Corp., is able to give voice to words that are printed on its display screen -- uncannily seeming to read its own mind. The second, from The Dun & Bradstreet Corp., is a credit and business information service that spews out verbal D&B reports in response to telephone queries. Both the DEC and D&B machines speak pleasantly, not in the somnolent drone we have assumed is the best computers can do, but in refreshingly cheerful and humanlike cadence.

Digital's DECtalk, a $4,000 device that plugs into any computer as easily as does a printer, is programmed to convert any text into speech by synthesizing a human voice digitally and playing the appropriate frequencies through a speaker. Its "voices" have been modulated into eight different characters, ranging in pitch from what sounds like a tinny-toned tot through a couple of female vocalizations down to a stentorian basso profundo named Harry. All of them pause at commas, raise their voices a little at question marks, and make forceful declarations at exclamation points.

Although English spelling is notorious for its irregularity, engineers have come up with enough contextual patterns so that even a word like "imbroglio" comes out accurately. What is more remarkable, the computer can toss off "rough," "through," "though," "cough," and "trough" without a hitch. In addition, a user can add in specialized jargon and acronyms. Because the upstart machine seems to think and talk so much like a person, there is a temptation to try to outsmart it, but that isn't easy to do. Even the sequence "St. Stephen's St." comes out right.

The system has talked its way into several jobs already. Children's Hospital Medical Center in Boston has installed a DECtalk system to teach speech-impaired youngsters. A major bank is using it to provide customers with bank balances over the phone. And MCI, the long-distance telephone company, will be connecting a system shortly so that a client can have messages read over the phone.

But in the long run, small businesses are likely to offer the widest market for DECtalk. With telephone read-back technology, for example, a salesperson can find out whether products are in stock at the warehouse, and an executive can call his or her office from anywhere and order an infinitely patient computer to sort through the electronic mail.

The Dun & Bradstreet product, called DunsVoice, uses a different voice-generation technology, with speech spliced together from snippets of actual human conversation. But one key part of the concept is the same: phoning in for spoken information. In D&B's case, a subscriber to the service can receive data for more than 5.3 million U.S. companies. By coding the transmission (that is what the * and # on the telephone can be used for), a woman's voice at the other end will reveal such details as a business's credit rating, payment habits, net worth, and condition. The information can be summoned via a local call to a microcomputing system, which then hooks in to D&B's central computers.

Although several million dollars was spent on its development, the fee for a DunsVoice report is considerably lower than regular printed D&B business reports, proving once again that talk is cheap.