How Does Speech Synthesis Work?

Text analysis and linguistic processing

Speech synthesizers are transforming workplace culture. A speech synthesis reads the text. Text-to-speech is when a computer reads a word aloud. It is to have machines talk simply and sound like people of different ages and genders. Text-to-speech engines are becoming more popular as digital services, and voice recognition grow.

What is speech synthesis?

Speech synthesis, also known as text-to-speech (TTS system), is a computer-generated simulation of the human voice. Speech synthesizers convert written words into spoken language.

Throughout a typical day, you are likely to encounter various types of synthetic speech. Speech synthesis technology, aided by apps, smart speakers, and wireless headphones, makes life easier by improving:

  • Accessibility: If you are visually impaired or disabled, you may use text to speech system to read text content or a screen reader to speak words aloud. For example, the Text-to-Speech synthesizer on TikTok is a popular accessibility feature that allows anyone to consume visual social media content.
  • Navigation: While driving, you cannot look at a map, but you can listen to instructions. Whatever your destination, most GPS apps can provide helpful voice alerts as you travel, some in multiple languages.
  • Voice assistance is available. Intelligent audio assistants such as Siri (iPhone) and Alexa (Android) are excellent for multitasking, allowing you to order pizza or listen to the weather report while performing other physical tasks (e.g., washing the dishes) thanks to their intelligibility. While these assistants occasionally make mistakes and are frequently designed as subservient female characters, they sound pretty lifelike.

What is the history of speech synthesis?

  • Inventor Wolfgang von Kempelen nearly got there with bellows and tubes back in the 18th century.
  • In 1928, Homer W. Dudley, an American scientist at Bell Laboratories/ Bell Labs, created the Vocoder, an electronic speech analyzer. Dudley develops the Vocoder into the Voder, an electronic speech synthesizer operated through a keyboard.
  • Homer Dudley of Bell Laboratories demonstrated the world’s first functional voice synthesizer, the Voder, at the 1939 World’s Fair in New York City. A human operator was required to operate the massive organ-like apparatus’s keys and foot pedal.
  • Researchers built on the Voder over the next few decades. The first computer-based speech synthesis systems were developed in the late 1950s, and Bell Laboratories made history again in 1961 when physicist John Larry Kelly Jr. gave an IBM 704 talk.
  • Integrated circuits made commercial speech synthesis products possible in telecommunications and video games in the 1970s and 1980s. The Vortex chip, used in arcade games, was one of the first speech-synthesis integrated circuits.
  • Texas Instruments made a name for itself in 1980 with the Speak N Spell synthesizer, which was used as an electronic reading aid for children.
  • Since the early 1990s, standard computer operating systems have included speech synthesizers, primarily for dictation and transcription. In addition, TTS is now used for various purposes, and synthetic voices have become remarkably accurate as artificial intelligence and machine learning have advanced.

How does Speech Synthesis Work?

Speech synthesis works in three stages: text to words, words to phonemes, and phonemes to sound.

1. Text to words

Speech synthesis begins with pre-processing or normalization, which reduces ambiguity by choosing the best way to read a passage. Pre-processing involves reading and cleaning the text, so the computer reads it more accurately. Numbers, dates, times, abbreviations, acronyms, and special characters need a translation. To determine the most likely pronunciation, they use statistical probability or neural networks.

Homographs—words that have similar pronunciations but different meanings require handling by pre-processing. Also, a speech synthesizer cannot understand “I sell the car” because “sell” can be pronounced, “cell.” By recognizing the spelling (“I have a cell phone”), one can guess that “I sell the car” is correct. A speech recognition solution to transform human voice into text even with complex vocabulary.

2. Words to phonemes

After determining the words, the speech synthesizer produces sounds containing those words. Every computer requires a sizeable alphabetical list of words and information on how to pronounce each word. They’d need a list of the phonemes that make up each word’s sound. Phonemes are crucial since there are only 26 letters in the English alphabet but over 40 phonemes.

In theory, if a computer has a dictionary of words and phonemes, all it needs to do is read a word, look it up in the dictionary, and then read out the corresponding phonemes. However, in practice, it is much more complex than it appears.

The alternative method involves breaking down written words into graphemes and generating phonemes that correspond to them using simple rules.

3. Phonemes to sound

The computer has now converted the text into a list of phonemes. But how do you find the basic phonemes the computer reads aloud when it converts text to speech in different languages? There are three approaches to this.

  • To begin, recordings of humans saying the phonemes will using.
  • The second approach is for the computer to generate phonemes using fundamental sound frequencies.
  • The final approach is to mimic the human voice technique in real-time by natural-sounding with high-quality algorithms.

Concatenative Synthesis

Speech synthesizers that use recorded human voices must be preloaded with a small amount of human sound that can be manipulated. Also, it is based on a human speech that has been recorded.

What is Formant Synthesis?

Formants are the 3-5 key (resonant) frequencies of sound generated and combined by the human vocal cord to produce the sound of speech or singing. Formant speech synthesizers can say anything, including non-existent and foreign words they’ve never heard of. Additive synthesis and physical modeling synthesis are used for generating the synthesized speech output.

What is Articulatory synthesis?

Articulatory synthesis is making computers speak by simulating the intricate human vocal tract and articulating the process that occurs there. Because of its complexity, it is the method that the least researchers have studied the least until now.

In short, voice synthesis software/ text-to-speech synthesis allows users to see written text, hear it, and read it aloud all at the same time. Different software makes use of both computer-generated and human-recorded voices. Speech synthesis is becoming more popular as the demand for customer engagement and organizational process streamlining grows. It facilitates long-term profitability.

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