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DECtalk was a speech synthesizer and text-to-speech technology developed by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

 in the early 1980s, based largely on the work of Dennis Klatt at MIT, whose source-filter algorithm was variously known as KlattTalk or MITalk.

The first DECtalk units were seen in 1984. They were standalone units that connected to any device with an asynchronous serial port
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...

. These units were also able to connect to the telephone system by having two telephone jacks. One connected to a phone line, the other to a telephone. The DECtalk units could recognize and generate any telephone touch tone. With that capability the units could be used to automate various telephone-related tasks by handling both incoming and outgoing calls. This included acting as an interface to an email system and the capability to function as an alerting system by utilizing the ability to place calls and interact via touch tones with the person answering the phone.

Later units were produced for PCs with ISA
Industry Standard Architecture
Industry Standard Architecture is a computer bus standard for IBM PC compatible computers introduced with the IBM Personal Computer to support its Intel 8088 microprocessor's 8-bit external data bus and extended to 16 bits for the IBM Personal Computer/AT's Intel 80286 processor...

 bus slots. In addition, various software implementations were produced, most notably the DECtalk Access32. Certain versions of the synthesiser were prone to undesirable characteristics. For example, the alveolar stops were often assimilated as sounding more like dental stops. Also, versions such as Access32 would produce faint electronic beeps at the end of phrases.

In the final years of DEC, the DECtalk IP was sold to Fonix Speech, Inc. (Now SpeechFX, Inc.), which offers DECtalk as a legacy TTS system.

The DECtalk engine was notably used in the National Weather Service
National Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...

's first "Console Replacement System" (CRS) installations in the late 1990s for NOAA Weather Radio. As of 2003 it had all but been replaced by a far more modern engine called Speechify. The so-called "Perfect Paul" voice (a DECtalk "preset" for a default understandable male voice) still does Station identification
Station identification
Station identification is the practice of radio or television stations or networks identifying themselves on air, typically by means of a call sign or brand name...

s on many NWR stations.

DECtalk can be used as an assistive technology for those unable to speak. A notable user is Stephen Hawking
Stephen Hawking
Stephen William Hawking, CH, CBE, FRS, FRSA is an English theoretical physicist and cosmologist, whose scientific books and public appearances have made him an academic celebrity...

, who is unable to speak due to a combination of severe disabilities caused by ALS
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis , also referred to as Lou Gehrig's disease, is a form of motor neuron disease caused by the degeneration of upper and lower neurons, located in the ventral horn of the spinal cord and the cortical neurons that provide their efferent input...

 as well as an emergency tracheotomy
Among the oldest described surgical procedures, tracheotomy consists of making an incision on the anterior aspect of the neck and opening a direct airway through an incision in the trachea...

. Hawking has used a DECtalk DTC01 voice synthesizer for several years and has come to be associated with the unique voice of the device. According to Hawking, he used the DTC01 for so long because he identified with it and had not heard a voice he liked better. However, he is now said to be using NeoSpeech's VoiceText speech synthesizer.