Diphone

A diphone is a segment of sound that represents the transition between two phonemes. In speech synthesis and signal processing, diphones are often used as the basic unit for constructing spoken words. When a speaker produces a continuous sound, the acoustic characteristics change over time. A diphone captures this gradual change, encompassing the part of the first phoneme up to its midpoint and the part of the second phoneme from its midpoint onwards.

The concept of diphones is fundamental to concatenative speech synthesis, a method where pre-recorded speech segments are joined together to form new utterances. By storing a database of diphones that cover all possible phoneme transitions in a language, a speech synthesizer can generate virtually any word or sentence by selecting and concatenating the appropriate diphones. This approach allows for a high degree of naturalness in the synthesized speech, as it preserves the coarticulatory effects inherent in human speech.

The quality of synthesized speech using diphones depends heavily on the size and accuracy of the diphone database, as well as the sophistication of the concatenation algorithm. Variations in pitch, duration, and spectral characteristics within diphones can be modeled and manipulated to enhance the expressiveness of the synthesized voice. While more advanced speech synthesis techniques exist, diphones remain a widely used and effective method for creating synthetic speech.