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59-426: Speechify is a mobile, chrome extension and desktop app that reads text aloud using a computer-generated text to speech voice. The app also uses optical character recognition technology to turn physical books or printed text into audio. The app lets users take photos of text and then listen to it read out loud. Speechify was founded by Cliff Weitzman , a dyslexic college student at Brown University who built
118-462: A 1791 paper. This machine added models of the tongue and lips, enabling it to produce consonants as well as vowels. In 1837, Charles Wheatstone produced a "speaking machine" based on von Kempelen's design, and in 1846, Joseph Faber exhibited the " Euphonia ". In 1923, Paget resurrected Wheatstone's design. In the 1930s, Bell Labs developed the vocoder , which automatically analyzed speech into its fundamental tones and resonances. From his work on
177-482: A database of speech samples. They can therefore be used in embedded systems , where memory and microprocessor power are especially limited. Because formant-based systems have complete control of all aspects of the output speech, a wide variety of prosodies and intonations can be output, conveying not just questions and statements, but a variety of emotions and tones of voice. Examples of non-real-time but highly accurate intonation control in formant synthesis include
236-415: A female voice. Kurzweil predicted in 2005 that as the cost-performance ratio caused speech synthesizers to become cheaper and more accessible, more people would benefit from the use of text-to-speech programs. The most important qualities of a speech synthesis system are naturalness and intelligibility . Naturalness describes how closely the output sounds like human speech, while intelligibility
295-543: A home computer. Many computer operating systems have included speech synthesizers since the early 1990s. A text-to-speech system (or "engine") is composed of two 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
354-492: A lack of universally agreed objective evaluation criteria. Different organizations often use different speech data. The quality of speech synthesis systems also depends on the quality of the production technique (which may involve analogue or digital recording) and on the facilities used to replay the speech. Evaluating speech synthesis systems has therefore often been compromised by differences between production techniques and replay facilities. Vocal tract The vocal tract
413-488: A number based on surrounding words, numbers, and punctuation, and sometimes the system provides a way to specify the context if it is ambiguous. Roman numerals can also be read differently depending on context. For example, "Henry VIII" reads as "Henry the Eighth", while "Chapter VIII" reads as "Chapter Eight". Similarly, abbreviations can be ambiguous. For example, the abbreviation "in" for "inches" must be differentiated from
472-617: A specialized software that enabled it to read Italian. A second version, released in 1978, was also able to sing Italian in an " a cappella " style. Dominant systems in the 1980s and 1990s were the DECtalk system, based largely on the work of Dennis Klatt at MIT, and the Bell Labs system; the latter was one of the first multilingual language-independent systems, making extensive use of natural language processing methods. Handheld electronics featuring speech synthesis began emerging in
531-411: A synthesizer can incorporate a model of the vocal tract and other human voice characteristics to create a completely "synthetic" voice output. The quality of a speech synthesizer is judged by its similarity to the human voice and by its ability to be understood clearly. An intelligible text-to-speech program allows people with visual impairments or reading disabilities to listen to written words on
590-468: A tool developed by ElevenLabs to create voice deepfakes that defeated a bank's voice-authentication system. The process of normalizing text is rarely straightforward. Texts are full of heteronyms , numbers , and abbreviations that all require expansion into a phonetic representation. There are many spellings in English which are pronounced differently based on context. For example, "My latest project
649-438: A waveguide or transmission-line analog of the human oral and nasal tracts controlled by Carré's "distinctive region model". More recent synthesizers, developed by Jorge C. Lucero and colleagues, incorporate models of vocal fold biomechanics, glottal aerodynamics and acoustic wave propagation in the bronchi, trachea, nasal and oral cavities, and thus constitute full systems of physics-based speech simulation. HMM-based synthesis
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#1732782753217708-411: Is speech recognition . 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,
767-442: Is a synthesis method based on hidden Markov models , also called Statistical Parametric Synthesis. In this system, the frequency spectrum ( vocal tract ), fundamental frequency (voice source), and duration ( prosody ) of speech are modeled simultaneously by HMMs. Speech waveforms are generated from HMMs themselves based on the maximum likelihood criterion. Sinewave synthesis is a technique for synthesizing speech by replacing
826-406: Is an important technology for speech synthesis and coding, and in the 1990s was adopted by almost all international speech coding standards as an essential component, contributing to the enhancement of digital speech communication over mobile channels and the internet. In 1975, MUSA was released, and was one of the first Speech Synthesis systems. It consisted of a stand-alone computer hardware and
885-466: Is another problem that TTS systems have to address. It is a simple programming challenge to convert a number into words (at least in English), like "1325" becoming "one thousand three hundred twenty-five". However, numbers occur in many different contexts; "1325" may also be read as "one three two five", "thirteen twenty-five" or "thirteen hundred and twenty five". A TTS system can often infer how to expand
944-531: Is built to adjust the intonation and pacing of delivery based on the context of language input used. It uses advanced algorithms to analyze the contextual aspects of text, aiming to detect emotions like anger, sadness, happiness, or alarm, which enables the system to understand the user's sentiment, resulting in a more realistic and human-like inflection. Other features include multilingual speech generation and long-form content creation with contextually-aware voices. The DNN-based speech synthesizers are approaching
1003-423: Is contained in the speech database. At runtime, the target prosody of a sentence is superimposed on these minimal units by means of digital signal processing techniques such as linear predictive coding , PSOLA or MBROLA . or more recent techniques such as pitch modification in the source domain using discrete cosine transform . Diphone synthesis suffers from the sonic glitches of concatenative synthesis and
1062-504: Is not always the goal of a speech synthesis system, and formant synthesis systems have advantages over concatenative systems. Formant-synthesized speech can be reliably intelligible, even at very high speeds, avoiding the acoustic glitches that commonly plague concatenative systems. High-speed synthesized speech is used by the visually impaired to quickly navigate computers using a screen reader . Formant synthesizers are usually smaller programs than concatenative systems because they do not have
1121-406: Is quick and accurate, but completely fails if it is given a word which is not in its dictionary. As dictionary size grows, so too does the memory space requirements of the synthesis system. On the other hand, the rule-based approach works on any input, but the complexity of the rules grows substantially as the system takes into account irregular spellings or pronunciations. (Consider that the word "of"
1180-415: Is quite successful for many cases such as whether "read" should be pronounced as "red" implying past tense, or as "reed" implying present tense. Typical error rates when using HMMs in this fashion are usually below five percent. These techniques also work well for most European languages, although access to required training corpora is frequently difficult in these languages. Deciding how to convert numbers
1239-452: Is realized as /ˌklɪəɹˈʌʊt/ ). Likewise in French , many final consonants become no longer silent if followed by a word that begins with a vowel, an effect called liaison . This alternation cannot be reproduced by a simple word-concatenation system, which would require additional complexity to be context-sensitive . Formant synthesis does not use human speech samples at runtime. Instead,
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#17327827532171298-407: Is segmented into some or all of the following: individual phones , diphones , half-phones, syllables , morphemes , words , phrases , and sentences . Typically, the division into segments is done using a specially modified speech recognizer set to a "forced alignment" mode with some manual correction afterward, using visual representations such as the waveform and spectrogram . An index of
1357-522: Is stored by the program. Determining the correct pronunciation of each word is a matter of looking up each word in the dictionary and replacing the spelling with the pronunciation specified in the dictionary. The other approach is rule-based, in which pronunciation rules are applied to words to determine their pronunciations based on their spellings. This is similar to the "sounding out", or synthetic phonics , approach to learning reading. Each approach has advantages and drawbacks. The dictionary-based approach
1416-787: Is the NeXT -based system originally developed and marketed by Trillium Sound Research, a spin-off company of the University of Calgary , where much of the original research was conducted. Following the demise of the various incarnations of NeXT (started by Steve Jobs in the late 1980s and merged with Apple Computer in 1997), the Trillium software was published under the GNU General Public License, with work continuing as gnuspeech . The system, first marketed in 1994, provides full articulatory-based text-to-speech conversion using
1475-413: Is the cavity in human bodies and in animals where the sound produced at the sound source ( larynx in mammals; syrinx in birds) is filtered. In birds , it consists of the trachea , the syrinx , the oral cavity, the upper part of the esophagus , and the beak . In mammals , it consists of the laryngeal cavity , the pharynx , the oral cavity, and the nasal cavity . The estimated average length of
1534-438: Is the ease with which the output is understood. The ideal speech synthesizer is both natural and intelligible. Speech synthesis systems usually try to maximize both characteristics. The two primary technologies generating synthetic speech waveforms are concatenative synthesis and formant synthesis . Each technology has strengths and weaknesses, and the intended uses of a synthesis system will typically determine which approach
1593-622: Is to learn how to better project my voice" contains two pronunciations of "project". Most text-to-speech (TTS) systems do not generate semantic representations of their input texts, as processes for doing so are unreliable, poorly understood, and computationally ineffective. As a result, various heuristic techniques are used to guess the proper way to disambiguate homographs , like examining neighboring words and using statistics about frequency of occurrence. Recently TTS systems have begun to use HMMs (discussed above ) to generate " parts of speech " to aid in disambiguating homographs. This technique
1652-566: Is used. Concatenative synthesis is based on the concatenation (stringing together) of segments of recorded speech. Generally, concatenative synthesis produces the most natural-sounding synthesized speech. However, differences between natural variations in speech and the nature of the automated techniques for segmenting the waveforms sometimes result in audible glitches in the output. There are three main sub-types of concatenative synthesis. Unit selection synthesis uses large databases of recorded speech. During database creation, each recorded utterance
1711-408: Is very common in English, yet is the only word in which the letter "f" is pronounced [v] .) As a result, nearly all speech synthesis systems use a combination of these approaches. Languages with a phonemic orthography have a very regular writing system, and the prediction of the pronunciation of words based on their spellings is quite successful. Speech synthesis systems for such languages often use
1770-446: Is very simple to implement, and has been in commercial use for a long time, in devices like talking clocks and calculators. The level of naturalness of these systems can be very high because the variety of sentence types is limited, and they closely match the prosody and intonation of the original recordings. Because these systems are limited by the words and phrases in their databases, they are not general-purpose and can only synthesize
1829-712: The German - Danish scientist Christian Gottlieb Kratzenstein won the first prize in a competition announced by the Russian Imperial Academy of Sciences and Arts for models he built of the human vocal tract that could produce the five long vowel sounds (in International Phonetic Alphabet notation: [aː] , [eː] , [iː] , [oː] and [uː] ). There followed the bellows -operated " acoustic-mechanical speech machine " of Wolfgang von Kempelen of Pressburg , Hungary, described in
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1888-628: The HAL 9000 computer sings the same song as astronaut Dave Bowman puts it to sleep. Despite the success of purely electronic speech synthesis, research into mechanical speech-synthesizers continues. Linear predictive coding (LPC), a form of speech coding , began development with the work of Fumitada Itakura of Nagoya University and Shuzo Saito of Nippon Telegraph and Telephone (NTT) in 1966. Further developments in LPC technology were made by Bishnu S. Atal and Manfred R. Schroeder at Bell Labs during
1947-446: The emotion of a generated line using emotional contextualizers (a term coined by this project), a sentence or phrase that conveys the emotion of the take that serves as a guide for the model during inference. ElevenLabs is primarily known for its browser-based , AI-assisted text-to-speech software, Speech Synthesis, which can produce lifelike speech by synthesizing vocal emotion and intonation . The company states its software
2006-492: The formants (main bands of energy) with pure tone whistles. Deep learning speech synthesis uses deep neural networks (DNN) to produce artificial speech from text (text-to-speech) or spectrum (vocoder). The deep neural networks are trained using a large amount of recorded speech and, in the case of a text-to-speech system, the associated labels and/or input text. 15.ai uses a multi-speaker model —hundreds of voices are trained concurrently rather than sequentially, decreasing
2065-661: The 1970s. LPC was later the basis for early speech synthesizer chips, such as the Texas Instruments LPC Speech Chips used in the Speak & Spell toys from 1978. In 1975, Fumitada Itakura developed the line spectral pairs (LSP) method for high-compression speech coding, while at NTT. From 1975 to 1981, Itakura studied problems in speech analysis and synthesis based on the LSP method. In 1980, his team developed an LSP-based speech synthesizer chip. LSP
2124-691: The 1970s. One of the first was the Telesensory Systems Inc. (TSI) Speech+ portable calculator for the blind in 1976. Other devices had primarily educational purposes, such as the Speak & Spell toy produced by Texas Instruments in 1978. Fidelity released a speaking version of its electronic chess computer in 1979. The first video game to feature speech synthesis was the 1980 shoot 'em up arcade game , Stratovox (known in Japan as Speak & Rescue ), from Sun Electronics . The first personal computer game with speech synthesis
2183-472: The TTS system has been tuned. However, maximum naturalness typically require unit-selection speech databases to be very large, in some systems ranging into the gigabytes of recorded data, representing dozens of hours of speech. Also, unit selection algorithms have been known to select segments from a place that results in less than ideal synthesis (e.g. minor words become unclear) even when a better choice exists in
2242-717: The acoustic patterns of speech in the form of a spectrogram back into sound. Using this device, Alvin Liberman and colleagues discovered acoustic cues for the perception of phonetic segments (consonants and vowels). The first computer-based speech-synthesis systems originated in the late 1950s. Noriko Umeda et al. developed the first general English text-to-speech system in 1968, at the Electrotechnical Laboratory in Japan. In 1961, physicist John Larry Kelly, Jr and his colleague Louis Gerstman used an IBM 704 computer to synthesize speech, an event among
2301-412: The combinations of words and phrases with which they have been preprogrammed. The blending of words within naturally spoken language however can still cause problems unless the many variations are taken into account. For example, in non-rhotic dialects of English the "r" in words like "clear" /ˈklɪə/ is usually only pronounced when the following word has a vowel as its first letter (e.g. "clear out"
2360-478: The database. Recently, researchers have proposed various automated methods to detect unnatural segments in unit-selection speech synthesis systems. Diphone synthesis uses a minimal speech database containing all the diphones (sound-to-sound transitions) occurring in a language. The number of diphones depends on the phonotactics of the language: for example, Spanish has about 800 diphones, and German about 2500. In diphone synthesis, only one example of each diphone
2419-515: The first version of the tool himself to help him keep up with his class readings. Text to speech 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 products. A text-to-speech ( TTS ) system converts normal language text into speech; other systems render symbolic linguistic representations like phonetic transcriptions into speech. The reverse process
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2478-425: The greatest naturalness, because it applies only a small amount of digital signal processing (DSP) to the recorded speech. DSP often makes recorded speech sound less natural, although some systems use a small amount of signal processing at the point of concatenation to smooth the waveform. The output from the best unit-selection systems is often indistinguishable from real human voices, especially in contexts for which
2537-563: The human vocal tract and the articulation processes occurring there. The first articulatory synthesizer regularly used for laboratory experiments was developed at Haskins Laboratories in the mid-1970s by Philip Rubin , Tom Baer, and Paul Mermelstein. This synthesizer, known as ASY, was based on vocal tract models developed at Bell Laboratories in the 1960s and 1970s by Paul Mermelstein, Cecil Coker, and colleagues. Until recently, articulatory synthesis models have not been incorporated into commercial speech synthesis systems. A notable exception
2596-526: The most prominent in the history of Bell Labs . Kelly's voice recorder synthesizer ( vocoder ) recreated the song " Daisy Bell ", with musical accompaniment from Max Mathews . Coincidentally, Arthur C. Clarke was visiting his friend and colleague John Pierce at the Bell Labs Murray Hill facility. Clarke was so impressed by the demonstration that he used it in the climactic scene of his screenplay for his novel 2001: A Space Odyssey , where
2655-531: The naturalness of the human voice. Examples of disadvantages of the method are low robustness when the data are not sufficient, lack of controllability and low performance in auto-regressive models. For tonal languages, such as Chinese or Taiwanese language, there are different levels of tone sandhi required and sometimes the output of speech synthesizer may result in the mistakes of tone sandhi. In 2023, VICE reporter Joseph Cox published findings that he had recorded five minutes of himself talking and then used
2714-412: The pronunciation of a word based on its spelling , a process which is often called text-to-phoneme or grapheme -to-phoneme conversion ( phoneme is the term used by linguists to describe distinctive sounds in a language ). The simplest approach to text-to-phoneme conversion is the dictionary-based approach, where a large dictionary containing all the words of a language and their correct pronunciations
2773-403: The required training time and enabling the model to learn and generalize shared emotional context, even for voices with no exposure to such emotional context. The deep learning model used by the application is nondeterministic : each time that speech is generated from the same string of text, the intonation of the speech will be slightly different. The application also supports manually altering
2832-512: The robotic-sounding nature of formant synthesis, and has few of the advantages of either approach other than small size. As such, its use in commercial applications is declining, although it continues to be used in research because there are a number of freely available software implementations. An early example of Diphone synthesis is a teaching robot, Leachim , that was invented by Michael J. Freeman . Leachim contained information regarding class curricular and certain biographical information about
2891-524: The rule-based method extensively, resorting to dictionaries only for those few words, like foreign names and loanwords, whose pronunciations are not obvious from their spellings. On the other hand, speech synthesis systems for languages like English, which have extremely irregular spelling systems, are more likely to rely on dictionaries, and to use rule-based methods only for unusual words, or words that are not in their dictionaries. The consistent evaluation of speech synthesis systems may be difficult because of
2950-665: The same year. In 1976, Computalker Consultants released their CT-1 Speech Synthesizer. Designed by D. Lloyd Rice and Jim Cooper, it was an analog synthesizer built to work with microcomputers using the S-100 bus standard. Early electronic speech-synthesizers sounded robotic and were often barely intelligible. The quality of synthesized speech has steadily improved, but as of 2016 output from contemporary speech synthesis systems remains clearly distinguishable from actual human speech. Synthesized voices typically sounded male until 1990, when Ann Syrdal , at AT&T Bell Laboratories , created
3009-454: The students whom it was programmed to teach. It was tested in a fourth grade classroom in the Bronx, New York . Domain-specific synthesis concatenates prerecorded words and phrases to create complete utterances. It is used in applications where the variety of texts the system will output is limited to a particular domain, like transit schedule announcements or weather reports. The technology
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#17327827532173068-508: The symbolic linguistic representation into sound. In certain systems, this part includes the computation of the target prosody (pitch contour, phoneme durations), which is then imposed on the output speech. Long before the invention of electronic signal processing , some people tried to build machines to emulate human speech. Some early legends of the existence of " Brazen Heads " involved Pope Silvester II (d. 1003 AD), Albertus Magnus (1198–1280), and Roger Bacon (1214–1294). In 1779,
3127-563: The synthesized speech output is created using additive synthesis and an acoustic model ( physical modelling synthesis ). Parameters such as fundamental frequency , voicing , and noise levels are varied over time to create a waveform of artificial speech. This method is sometimes called rules-based synthesis ; however, many concatenative systems also have rules-based components. Many systems based on formant synthesis technology generate artificial, robotic-sounding speech that would never be mistaken for human speech. However, maximum naturalness
3186-405: 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. 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
3245-447: The units in the speech database is then created based on the segmentation and acoustic parameters like the fundamental frequency ( pitch ), duration, position in the syllable, and neighboring phones. At run time , the desired target utterance is created by determining the best chain of candidate units from the database (unit selection). This process is typically achieved using a specially weighted decision tree . Unit selection provides
3304-496: The vocoder, Homer Dudley developed a keyboard-operated voice-synthesizer called The Voder (Voice Demonstrator), which he exhibited at the 1939 New York World's Fair . Dr. Franklin S. Cooper and his colleagues at Haskins Laboratories built the Pattern playback in the late 1940s and completed it in 1950. There were several different versions of this hardware device; only one currently survives. The machine converts pictures of
3363-446: The word "in", and the address "12 St John St." uses the same abbreviation for both "Saint" and "Street". TTS systems with intelligent front ends can make educated guesses about ambiguous abbreviations, while others provide the same result in all cases, resulting in nonsensical (and sometimes comical) outputs, such as " Ulysses S. Grant " being rendered as "Ulysses South Grant". Speech synthesis systems use two basic approaches to determine
3422-586: The work done in the late 1970s for the Texas Instruments toy Speak & Spell , and in the early 1980s Sega arcade machines and in many Atari, Inc. arcade games using the TMS5220 LPC Chips . Creating proper intonation for these projects was painstaking, and the results have yet to be matched by real-time text-to-speech interfaces. Articulatory synthesis consists of computational techniques for synthesizing speech based on models of
3481-466: Was Manbiki Shoujo ( Shoplifting Girl ), released in 1980 for the PET 2001 , for which the game's developer, Hiroshi Suzuki, developed a " zero cross " programming technique to produce a synthesized speech waveform. Another early example, the arcade version of Berzerk , also dates from 1980. The Milton Bradley Company produced the first multi-player electronic game using voice synthesis, Milton , in
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