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.