What is speech synthesis and how is it used?

Speech synthesis uses complex al­go­rithms to output texts as spoken words using a simulated voice. The benefits of speech synthesis include better ac­ces­si­bil­i­ty and dis­sem­i­na­tion of in­for­ma­tion, a per­son­al­ized user ex­pe­ri­ence and more efficient in­ter­ac­tions.

What is speech synthesis?

Speech synthesis, often referred to as text-to-speech (TTS), is a tech­nol­o­gy that turns written text into spoken language and outputs it using a simulated voice that closely mimics natural human speech. TTS tech­nol­o­gy uses stored speech segments to generate an ar­ti­fi­cial voice that re­pro­duces texts as acoustic signals, so that it sounds as authentic and natural as possible. While earlier TTS tech­nolo­gies still strung together fixed strings of words or sentences, modern speech synthesis is able to achieve different lin­guis­tic nuances and emphases and in­tel­li­gent­ly combine speech segments to create original content.

Speech synthesis is ideal for cost ef­fec­tive­ly conveying texts, messages and in­for­ma­tion without human speakers and op­ti­miz­ing com­mu­ni­ca­tion, ac­ces­si­bil­i­ty and reach. For this reason, speech synthesis is used in various in­dus­tries and for various purposes, both com­mer­cial­ly and in areas such as education, service or nav­i­ga­tion.

How does speech synthesis work?

The speech synthesis process usually begins with inputting written content such as messages, texts, ad­ver­tis­ing messages or emails. The software then converts the text into simulated, natural-sounding speech using different tech­nolo­gies like al­go­rithms, pre-recorded speech signals, neural networks, ar­ti­fi­cial in­tel­li­gence and machine learning. In order to achieve an output that sounds as natural as possible, the tone of voice, in­to­na­tion and style of speech are adapted as closely as possible to a human way of speaking.

In the early days of speech synthesis, canned speech was used, i.e., pre-recorded words and sentences that were strung together to create familiar robotic voices. Nowadays, TTS software is able to draw on a large database of speech signals and segments to ensure flexible and natural speech gen­er­a­tion, even for un­fa­mil­iar texts.

In addition, tech­nolo­gies such as acoustic models, formant synthesis, ar­tic­u­la­to­ry synthesis and overlap add are used to break down text into audio signals and syn­the­size spoken word sequences, speech rate, prosody and in­to­na­tion as naturally as possible.

How is speech synthesis used?

Speech synthesis can be used for a broad spectrum of use cases, including:

• Ac­ces­si­ble tech­nolo­gies: Speech synthesis software makes it possible, among other things, for people with visual im­pair­ments to have texts read out. With screen readers, blind and visually impaired people can navigate computers in­de­pen­dent­ly, access in­for­ma­tion, produce trans­la­tions and even display syn­the­sized speech in Braille.
• Education and training: Speech synthesis software can be used to make record­ings and tran­scrip­tions of lectures, teaching materials or con­fer­ences ac­ces­si­ble. It also allows for efficient dis­tri­b­u­tion of these materials. Authors and editors can also check texts for errors and com­pre­hen­si­bil­i­ty by listening to them read aloud.
• Podcasts, audio blogs and audiobook pro­duc­tion: For popular audio formats such as podcasts, audio blogs or au­dio­books, speech synthesis enables fast, cost-effective and high-quality pro­duc­tion. Instead of finding voice actors, pro­fes­sion­al audio content can be produced cost ef­fec­tive­ly and to a high standard using TTS. It can be output as MP3 files or in streaming formats.
• Telephone an­nounce­ments and customer service: Whether for automated telephone and loud­speak­er an­nounce­ments or customer service systems, in the business world, speech synthesis enables efficient support for customers and fast inquiry pro­cess­ing.
• Nav­i­ga­tion systems: Speech synthesis plays an important role in the field of nav­i­ga­tion systems and is used in GPS devices and nav­i­ga­tion apps. It provides better service, modern au­toma­tion and greater safety in public transport through traffic in­for­ma­tion, route and driving in­struc­tions and automatic stop an­nounce­ments.
• En­ter­tain­ment and media: In en­ter­tain­ment media such as video games, animated films, doc­u­men­taries or other in­ter­ac­tive formats, speech synthesis enhances immersive gaming ex­pe­ri­ences and gives ar­ti­fi­cial char­ac­ters realistic, lifelike speech.
• Automated voice services and voice as­sis­tants: Thanks to speech synthesis, you can enhance virtual as­sis­tants and enable functions with spoken voice output or control, whether for voice search SEO, voice search op­ti­miza­tion, voice as­sis­tants, chatbots or gen­er­a­tive AI.

With TTS, you can not only use pre­de­fined neural voices but also create your own neural voices or simulate real voices through record­ings. This means that ar­ti­fi­cial voices can be adapted to product and company brands, ad­ver­tis­ing campaigns, voice apps or even content such as audio books and podcasts.

What’s the dif­fer­ence between speech synthesis and speech recog­ni­tion?

Speech synthesis trans­forms written content into spoken language by using computer-generated voices to reproduce texts acousti­cal­ly. Speech recog­ni­tion, on the other hand, is designed to un­der­stand spoken language and convert it into written text by con­vert­ing the acoustic ut­ter­ances into digital char­ac­ters. In short, speech synthesis is the coun­ter­part to speech recog­ni­tion as it converts text into spoken language, while speech recog­ni­tion converts spoken language into written text.

Speech synthesis and speech recog­ni­tion are often closely linked and are fre­quent­ly used together in voice as­sis­tance systems. Speech synthesis is used to provide users with answers in spoken form. Speech recog­ni­tion is re­spon­si­ble for ensuring that the system un­der­stands the requests and responds ac­cord­ing­ly. These tech­nolo­gies com­ple­ment each other perfectly, con­tribut­ing to improved human-machine in­ter­ac­tion.

Other types of speech synthesis

In addition to pure text-to-speech software, speech synthesis offers other speech systems such as:

• Speech pros­the­sis: Speech pros­the­ses help people with physical or speech dis­abil­i­ties to produce natural speech using computer-generated speech systems and minimal input. They are designed to promote ac­ces­si­bil­i­ty and fa­cil­i­tate com­mu­ni­ca­tion and access to computers.
• Mul­ti­modal speech synthesis: Mul­ti­modal speech synthesis, also known as au­dio­vi­su­al speech synthesis, uses syn­the­sized speech in com­bi­na­tion with animated faces to sup­ple­ment speech with visual signals and facial ex­pres­sions such as smiling or shaking one’s head. In this way, the ex­pres­sive­ness, live­li­ness, nat­u­ral­ness and nuance of speech synthesis can be improved.