Speech Synthesis

Speech synthesis is the artificial production of human speech. A computer system designed for this purpose is referred to as a speech synthesizer. These systems can be implemented in either software or hardware products, and they serve various applications, from assisting the visually impaired to enabling hands-free communication.

Components and Functionality

A core function of speech synthesizers is text-to-speech (TTS) conversion. This process involves transforming written text into audible speech. TTS systems are capable of converting normal language text into speech, while other systems are designed to convert symbolic linguistic representations like phonetic transcriptions into speech.

The reverse of speech synthesis is speech recognition, which involves interpreting spoken words into text or commands that a machine can understand and act upon.

Methods of Speech Synthesis

One method of generating synthesized speech involves concatenating segments of recorded speech that are stored within a database. The granularity of these stored speech units typically ranges from phones to diphones, which can influence the clarity and naturalness of the output.

Alternatively, some speech synthesizers use a model of the human vocal tract and other characteristics of human voice to create a wholly synthetic voice output. This approach often strives to achieve high-quality speech that is hard to distinguish from a human voice, thereby enhancing the user experience.

Evaluation of Speech Synthesizers

The effectiveness of a speech synthesizer is judged on its ability to closely mimic human speech and its intelligibility. High-quality systems are expected to provide clear and understandable speech output, which is crucial for their application in real-world scenarios such as navigation systems, assistive technologies, and interactive voice response systems.

Historical Context and Development

The development of speech synthesizers has a rich history, with significant contributions from various companies and technologies. For instance, the DECtalk system, developed by Digital Equipment Corporation in 1983, was a notable advancement in TTS technology. Similarly, the Texas Instruments LPC Speech Chips played a crucial role in speech synthesizer development by implementing linear predictive coding techniques.

Another prominent example includes the Votrax synthesizers, which were derived from designs created by Richard T. Gagnon in the 1970s.

Modern Applications

Today, speech synthesizers are integral to various sectors. They are embedded in virtual assistants like Amazon Alexa and Apple Siri, and are critical in providing accessibility solutions for individuals with disabilities. The Microsoft Speech API also offers a platform for developers to integrate TTS capabilities into applications.