How Speech Synthesis Works – Complete Guide
Speech Synthesis software are transforming the work culture of different industry sectors. A speech synthesizer is a computerized voice that turns a written text into a speech. It is an output where a computer reads out the word loud in a simulated voice; it is often called text-to-speech. It is not only to have machines talk simply but also to make a sound like humans of different ages and gender. With the rise of usage of digital services and the increase in dependency on voice recognition, the text-to-speech engine is gaining popularity.
How does Speech Synthesis Work?
There are 3 stages in which speech synthesis works; text to words, words to phonemes, and phonemes to sound.
Text to words –
The initial stage of speech synthesis, is generally called pre-processing or normalization, it is everything about reducing ambiguity: it’s about narrowing down the many different ways a person could read a piece of text into the one that’s the most appropriate. In Pre-processing it’s about going through the text and then cleaning it up so the computer makes fewer mistakes when it reads the words aloud. Elements like numbers, dates, times, abbreviations, acronyms, and special characters need to be turned into words.
This is however harder than it sounds. For example; the number 1953 might refer to several items, a year or a time, or a padlock combination; each of these is read out will sound slightly differently. While humans can figure out the pronunciation based on the way the text is written, computers generally don’t have that ability to do that.
This is the reason they use statistical probability techniques or neural networks to arrive at the most likely pronunciation. If there were a decimal point before the numbers (“.953”), then it would be read differently as “nine fifty-three.”
Pre-processing also handles homographs, these are the words pronounced in different ways but the meaning is different for each word. The word “sell” can be pronounced as “cell”, so a sentence such as “I sell the flower” is problematic for a speech synthesizer. But if it can understand that the preceding text entirely has a different meaning, by recognizing the spelling (“I have a cell phone”), then it can make a reasonable guess that “I sell the pen” is likely correct.
Words to phonemes –
Once they figure out the words that need to be spoken, next the speech synthesizer has to generate the speech sounds that make up these words. Every computer needs is a huge alphabetical list of words and details of how to pronounce each word. For each word, they would need a list of the phonemes that make up its sound.
Theoretically, if a computer has a dictionary of words and phonemes, then all it needs to do is to read a word and look it up in the list, and then read out the corresponding phonemes. But practically, it’s quite harder than it sounds.
The alternative approach involves breaking down the written words into their graphemes (written component units, typically made from the individual letters or syllables that make up a word) and then generate phonemes that correspond to them using a set of simple rules. The benefit of doing this is that the computer can make a reasonable attempt at reading any word.
Phonemes to sound –
At this point, the computer has converted the text into a list of phonemes. But how to find basic phonemes that the computer reads aloud when it’s turning the text into speech. There are three different approaches to this.
- First to use recordings of humans saying the phonemes
- The second is for the computer to generate the phonemes itself by generating basic sound frequencies
- The last approach is to imitate the technique of the human voice.
The speech synthesizers that use recorded human voices, have to be preloaded with a bit of human sound they can rearrange. It is based on recorded human speech.
Formants are the 3–5 key (resonant) frequencies of sound that the human vocal cord generates and combines to make the sound of speech or singing. Formant speech synthesizers can say anything, even the words that don’t exist or foreign words they’ve never heard off. The synthesized speech output is created using additive synthesis and physical modeling synthesis.
Articulatory synthesis means making computers speak by modelling the intricate human vocal tract and articulate the process occurring there. It is the least explored method, due to its complexity.
Usage of the Speech Synthesizer
The application of Speech Synthesis software is growing rapidly due to its multiple applications. It is also becoming affordable for the common people, which makes it very appropriate for daily use. Currently, speech synthesis is used to read www-pages or other forms of media with a normal personal computer. In short, a speech synthesizer can be used in all kinds of human-machine interaction.
For Blind People –
The most important usage of speech synthesis software is for helping the blind to read and communicate. As the blind person cannot see the length of an input text when starting to listen to it with a speech synthesizer, so in advance giving some information of the text to be read is quite helpful. Additionally, the bold or underlined text information may be given with a slight change of intonation or loudness.
For Education –
Synthesized speech can also be used for many educational purposes. It can be programmed for special tasks like teaching spelling and pronunciation of different languages. Also, it can be used with interactive educational applications.
For Telecommunications and Multimedia –
For a long time, synthesized speech is used in different kinds of telephone inquiry systems. Whereas its application in multimedia is new. With the synthesized speech, the e-mail messages can listen via the normal telephone line. It may also be used to speak out SMS on mobile phones.
Some of the speech recognition software are discussed below:
Human speech is quite complex, so the text-to-speech engines provides good accuracy in understanding the speech due to its technological advancement. The Speech Recognition software deals with different types of speech patterns and individuals’ accents. The best free speech synthesizer has a lot of usage in computing, helps visually impaired or people having Dyslexia and more.
The Speech Recognition software helps companies to save time and money by mechanizing the business processes, it is quite cost-effective as it performs speech recognition and transcription faster and accurately than a human and it is to use and readily available. Below are some of the free Speech Recognition software which provides ease of use, accuracy, comprehension, and more.
- Google Now is a feature of Google search of the Google app for Android and iOS platforms.
- Siri is a built-in, voice control virtual assistant, incorporated as a feature of the Apple iPhone.
- Cortana, developed by Microsoft is a virtual assistant, it uses the Bing search engine to perform certain tasks like setting reminders and answering questions for the user.
- Simon is made for the free and open source. It permits customization for applications wherever speech recognition is required. Also, work with any dialect and is not bound to any language.
- Kaldi is a free open source speech recognition software that is freely available under the Apache License. It is mostly used for acoustic modelling research.
Below are some of the paid speech recognition software
- Dragon Anywhere helps a person dictate and edit documents by voice on his iOS or Android mobile device quickly and accurately.
- Amazon Lex is a service to build conversational interfaces into any application using voice and text.
- Dragon Professional is a dictation and voice recognition software
- Voice Finger is a speech recognition tool that enables a person to control his mouse and keyboard
- Tazti supports the Windows operating system and it is used to control applications, games, and robots.
Below listed are some of the best free speech synthesizer available in the market. Some of them are discussed below.
- Acapela Group Virtual Speaker is one of the BEST FREE SPEECH SYNTHESIZER useful for eLearning purposes. It has many compatible formats, languages, and voice properties.
- AudioBookMaker provides a multi-lingual interface, customizable speech parameters, and highlighted spoken text, and customized settings.
- Balabolka is a free speech synthesizer with customizable voices. Additionally, it can also save narrations as audio files in formats including MP3 and WAV.
- Natural Reader is used for loading documents into its library and then reading them aloud from there. Also, it takes the form of a floating toolbar. In this situation, one can highlight text in any application and use the toolbar controls to start and customize the text to speech.
- Panopreter Basic software takes plain and rich text files, web pages, and Microsoft Word documents as input, and exports the resulting sound in both WAV and MP3 format.
Speech synthesis technology when combined with AI boosts the marketing campaigns of organizations. It helps personalize their solutions by creating a brand voice. The natural, human-like voices convert text to speech. Natural voice interactions help engage customers. Differentiating is the key to long term sustenance for organizations in today’s date.
Organizations assist hands-on with cloud or on-premise deployment so that the digital transformation becomes easier. With the help of deep learning, technology is striking a balance between custom voices and human interaction. They help strike consistency with multi-modal systems.
The concept of speech synthesis was first introduced to the world in 1779 by Christian Kratzenstien. He was a professor who created an apparatus based on the human vocal tract. This was created to showcase vowel sound differences. VODER or Voice Operating Demonstrator was the first voice synthesizer that was showcased in the 1939 World’s fair. It was based on Bell laboratories’ voice coder or vocoder.
The technology driving speech recognition is improvising at multiple levels every day. Accuracy is the objective of the research.
The spoken language interface has been improvising over the past years. The reason behind this is to reduce the discomfort caused by talking to machines. There is a wide scope of improvement. Speech can replace warning lights or buzzers as well.
Usability has increased in mobile phones, videoconferences, or videophones. In the past few decades, speech has been used to improvise and develop talking calculators for modern audio-visual applications that are three dimensional.
According to research, articulatory synthesis is considered to be the most accurate method as compared to Concatenative synthesis, which is gaining popularity. Articulatory synthesis is quite too difficult to approach. Due to its multidimensional nature, there are multiple evaluation features in speech and tests to analyze quality.
There are different types of voice synthesizer software available for different types of needs. But before opting for any of the above-mentioned software, the user has to evaluate their business needs and then decide. One of the most common usages of voice recognition software is virtual assistance. There are also many other uses like online banking; the banking and finance sector start-ups are one of the earliest adopters of this technology.
Voice transcription solution is quite helpful for the healthcare industry, which facilitates storing, structuring, and accessing information about patients’ medical records. Another usage is voice biometry, which allows organizations to create a digital profile of a person’s voice, by analyzing a series of specific characteristics such as tone, pitch, intensity, dynamics, dominant frequencies, and others.
In short, the voice synthesizer software allows users to see text and hear it and then read aloud simultaneously. Both the computer-generated voice and human recorded voice are used by different software. The rising need of customer engagement and organization process streamlining demands, speech synthesis is gaining popularity. It is a facilitator of long-term profitability.
Kwantics’ Speech AI solutions can make custom voices for your business or brand. Check out our enterprise level AI solutions for speech synthesis. We are offering a live demo of our AI-Powered solution to answer your queries.