Speech Technologies

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Speech technologies are technologies or devices that can understand and/or produce human-like speech. The speech generation is useful in applications such as text-to-speech, electrolarynges, speech prostheses, or intelligent personal assistants. The former three technologies are used as medical devices for people who have lost their voice. Speech synthesizers are also incorporated into devices that help visually disabled people. Intelligent personal assistants allow users to use their devices hands-free by merely saying required commands, mostly in plain, natural speech.

These speech technologies deal with the voice, which is the dominant tool of interpersonal communication.[1] The importance of the voice was acknowledged also by the fact that 16th April was chosen as World Voice Day.[2]

Main Characteristics

Speech technologies can be divided between technologies used in medicine and technologies for commercial use. While the former group is represented primarily by electrolarynges and speech prostheses, intelligent personal assistants belong to the latter category. Speech synthesis is used for both purposes. It is contained in intelligent personal assistants and GPS navigations, but also in systems for the visually impaired and speech synthesizers for people who have lost their voice.[3] These technologies appear in two forms: devices or software, or a combination of both.

Historical overview

The first speaking machines were developed in antiquity and the Middle Ages. Nonetheless, they were not genuine speaking machines, since they depended on people speaking inside of them. The first genuine speaking machine was introduced by Hungarian civil servant and inventor Wolfgan von Kempelen. He described his speech synthesiser in the book Mechanismus der menschlichen Sprache nebst der Beschreibung seiner sprechenden Maschin [The Mechanism of Human Speech, with a Description of a Speaking Machine], published in 1791.[4]

Theodore Billroth conducting a laryngectomy

In the 19th century, researchers focused also on helping people who lost their voice or have a serious problem with their throat. Jan Nepomuk Czermak described the first laryngeal prosthesis in 1859. His attempt was followed by the introduction of various speech prostheses and artificial larynges.[5] Later on, Austrian surgeon Theodore Billroth performed the first successful total extirpation of the larynx.[6]

The 20th century showed important breakthroughs in various fields of speech technologies. Speech synthesis started to be mechanized by the introduction of the first known electrical system, 'The Voder' in 1930.[7] New techniques of voice synthesis also made the synthetic voice to sound more natural and lately to allow the preservation of the voices of patients who are losing their voice.[8] The first electrolarynges were introduced in 1942 by G. M. Wright.[5] Surprisingly, the first tracheoesophageal voice prosthesis was not developed by a professional, but it was conducted by a patient using a red-hot ice pick in 1931. Surgeons, however, were unable to replicate this procedure.[9] Therefore, it was abandoned until Erwin Mozolewski presented his tracheoesophageal voice prosthesis.[10]

In the middle of the 20th century, the first speech recognition system was introduced. The first system was 'Audrey' which was able to recognise digits spoken by a single voice. It was followed by IBM's 'Shoebox' presented at the 1962 World's Fair. It was able to recognise 16 English words. Another important system for voice recognition was 'Harpy', which was developed by the U.S. Department of Defense between 1971 and 1976. It could recognise 1,011 words, similar to the capabilities of a 3 year-old child.[11] Apple presented the idea of an intelligent personal assistant in 1987. It was entitled Knowledge Navigator, but the advertised product was never developed.[12] The first publicly available personal assistant was Siri, introduced by Apple in 2010.[13] It was followed by the similar products of other companies as Alexa, Google Now, and Cortana.[14] Siri was software that was contained in iPhones. In 2014, Amazon.com presented its first intelligent personal assistant device Amazon Echo, which contains Alexa.[15] Its introduction also provoked the introduction of similar devices such as Google Home, Apple HomeKit, Lenovo Smart Assistant, etc.[14]

Important Dates

  • 1769: Wolfgang von Kempelen developed the first genuine speech synthesizer[16]
  • 1859: the first pneumatic laryngeal prosthesis was introduced by Jan Nepomuk Czermak[5]
  • 1873: Billroth conducted the first successful total laryngectomy[5]
  • 1931: the first laryngeal puncture was conducted by a patient[17]
  • 1937: the speech synthesizer 'The Voder' was unveiled[7]
  • 1942: Wright developed the first electrolarynx 'Sonovox'[18]
  • 1952: Bell Laboratories presented 'Audrey'[11]
  • 1972: Erwin Mozolewski introduced a tracheoesophageal voice prosthesis[19]
  • 1976: 'Harpy' was developed[11]
  • 1987: the Apple Knowledge Navigator was presented[20]
  • 4th February 2010: Siri Inc. unveiled Siri, which was later acquired by Apple[13]
  • 6th November 2014: Amazon.com introduced Amazon Echo[15]


Therapy & Treatment

Stephen Hawking, the most renowned user of speech synthesis

The purpose of speech prostheses and electrolarynges is to return the ability to speak to patients who have undergone total laryngectomy or lost their voice in some other way.[21] Certain speech synthesizers could also be used for this purpose, even though speech synthesis is used also in non-therapeutic applications.[3] Patients could also achieve oesophageal speech, but it is difficult to learn, and certain patients are not able to communicate this way.[22] Each technique of voice restoration has its pros and cons. The electrolarynx's speech sounds mechanical and depends on the mechanical device, but it is easy to achieve, and it is used when any other methods have failed.[21] Speech prostheses have to be installed during surgery, the prosthesis has to be removed periodically[23], and the pitch is considerably low for women,[24] but in comparison to electrolarynx, prostheses have certain pitch control and are more intelligible.[23] Speech synthesis could preserve a patient's voice, but it depends on the voice conservation, which could be challenging.[8]

Customers' reviews suggest that intelligent personal assistants could be helpful for the elderly and disabled. These devices could make them more independent due to control of the environment which they provide.[25] Customers also claim that the devices could call for help when elderly or disabled people have an accident,[26] though, this claim has not yet been supported by research.

Speech synthesis is used in various applications and devices for the blind or people with vision impairments. It enables them to read content from a screen.[8] Speaking devices used as toys or GPS systems also benefit from speech synthesis. They are also used in call centres, where they handle common tasks of customers.[3]


Intelligent personal assistants (IPA) are meant to help users deal with several tasks, organise information, and provide help with complex tasks. Siri, the first IPA, was originally developed to solve military tasks[27]. However, IPAs are also currently used in medical care,[28] business, transportation,[29] and shopping[30]. IPAs could also control the smart devices which are in the household of their users, even though certain brands support only certain IPAs.[31] IPAs or speech synthesizers could help their users with the acquisition of foreign language.[32][33][34]

Ethical & Health Issues


The issue with which every speech technology struggles, is efficiency and quality of performance. As was mentioned in a previous section, the quality of the voice produced by the electrolarynx is low, even though newly introduced electrolarynges contain pitch control.[18] Although the voice produced by voice prostheses and speech synthesizers sounds better, it is still not natural.[3][24][35] Finally, intelligent personal assistants struggle with the recognition of different accents,[36] are only as efficient as the applications with they are compatible, and run only on their home device at the moment.[37]

Microsoft's Cortana, intelligent personal assistant

Privacy issues

The main issue linked with IPAs is data collection. IPAs collect various data about their users as personal contacts, location, and preferences, etc., in order to provide adequate service. Moreover, their speech synthesis is not processed at the device but in the remote centre.[38] These data are valuable for the companies, that collect them and can be used for their commercial purposes.[39] The data could also be misused, if they are stolen by a third party.[40] The majority of IPAs listen to all of the communication which happens around them. Although it could be switched off, this feature is not always used, since it is inconvenient.[41] The issue applies to some extent also with regard to speech synthesizers, especially on apps, which provide speech synthesis.[42]


The problem of 'uncanny valley' could also be applied on within speech technologies. Jan Romportl claims that the effect of uncanny valley have caused the more natural-sounding voices produced by current speech synthesizers to not have been entirely accepted.[43] In addition, the Gatebox IPA caused a controversy and was deemed to be creepy by certain journalists due to the fact that it tends to be considerably personal.[44] Nicholas Brazzi also warns that the personal connection to IPAs could have a negative effect on decision making and could be potentially dangerous and life-threatening.[45]

Post-surgery state

The use of certain types of electrolarynges and speech synthesizers could be limited after surgery due to the post-surgery state of the patient. Patients could be weak[46] and the tissue in his or her neck could be harmed by surgery or radiation. While certain conditions could change in a few days after surgery, if the tissue is scarred or radiated, the patient could not use a neck-type electrolarynx.[47]


Intra-oral electrolarynges tend to be corrupted by infection, and therefore patients have to care for them carefully.[48] The appropriate hygiene is also necessary in the handling of speech prostheses.[49]

Public & Media Impact and Presentation

Electrolarynx Guy from My Name Is Earl

Speech technologies feature in several sci-fi films, series, books, and video games. One of the best known is HAL from Stanley Kubrick's 2001: A Space Odyssey. It is a computer that turned to endanger the staff of the spaceship where installed. When it is switched off he sang Daisy Bell. Arthur C. Clark, the author of the plot, was inspired by his experience with a real computer that was able to sing this song.[50]

Several speech technologies, which are already available, also appear on screen. An electrolarynx was used by characters in Mad Max[51], South Park,[52] and My Name Is Earl[53]. Siri, an Apple's IPA, appeared in The Big Bang Theory[54], where one of the main characters falls in love with her, and was parodied in The Simpsons[55].

The most renowned user of speech synthesis might be Stephen Hawking, British physicist and cosmologist. Hawking lost his voice due to a tracheotomy that he underwent in 1985. He uses a system that Intel developed for him.[56] Intel released this software, which is entitled ACAT, for free. It is meant to help patients with the same diagnosis as Hawking has, amyotrophic lateral sclerosis, as well as other disabled people.[57]

Loss of voice is caused by total laryngectomy due to a cancer in many cases. The main factor causing this type of cancer is smoking. Therefore, people who use electrolarynx or speech prostheses are involved in several anti-smoking campaigns, e.g., a cowboy singing with his electrolarynx a song with the refrain 'You don't always die from tobacco',[58] or a man with an electrolarynx who sold cigarettes and told the story of his life.[59]

Public Policy

Devices that collect personal data have to comply with certain regulations.[60] In addition, their use is banned in some companies, e.g., IBM.[61]

Related Technologies, Projects or Scientific Research

IBM works on the enrichment of speech synthesis by emotions.[62]

Several devices which are listed among the Internet of Things (IoT) could be controlled by an IPA.[31]


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