Speech synthesis, also called text-to-speech (TTS), is the artificial production of human speech. It involves converting text input into a waveform or audio file, which can be played back on a computer or other device. Speech synthesis is used in a variety of applications, such as:
- Virtual assistants, such as Siri and Alexa, use speech synthesis to provide spoken responses to user queries.
- Educational software, such as reading tutors, use speech synthesis to read aloud text passages to students.
- Media players, such as VLC and QuickTime, use speech synthesis to provide audio descriptions of videos for visually impaired users.
- Telephone systems, such as automated answering services, use speech synthesis to provide recorded messages to callers.
Speech synthesis is a complex process that involves a number of steps. The first step is to convert the text input into a phonetic representation. This can be done using a variety of methods, such as:
- Rule-based methods, which use a set of rules to map text characters to phonemes.
- Statistical methods, which use statistical models to learn the mapping between text and phonemes.
- Neural network methods, which use neural networks to learn the mapping between text and phonemes.
Once the text input has been converted into a phonetic representation, the next step is to generate a waveform or audio file. This can be done using a variety of methods, such as:
- Concatenative synthesis, which involves concatenating together pre-recorded phonemes.
- Recurrent neural network (RNN) synthesis, which involves using a RNN to generate the waveform directly from the phonetic representation.
- WaveNet synthesis, which involves using a WaveNet, a type of generative adversarial network (GAN), to generate the waveform directly from the phonetic representation.
The final step in the speech synthesis process is to apply a variety of post-processing effects to the generated waveform. This can include:
- Noise reduction, to remove unwanted noise from the waveform.
- Equalization, to adjust the frequency balance of the waveform.
- Compression, to reduce the dynamic range of the waveform.
Speech synthesis is a rapidly developing field, and new techniques are constantly being developed to improve the quality of the generated speech. As a result, speech synthesis is becoming increasingly more widely used in a variety of applications.