A vocoder (voice encoder) is a device that was originally developed for low bandwidth transmission of voice messages, but is now used for special voice effects in music production.
The original idea behind the vocoder was to encode the essence of the human voice by extracting just the most basic elements – the consonant sounds made by the vocal chords and the vowel sounds made by the modulating effect of the mouth. The consonants serve as the carrier signal and the vowels (also called formants) serve as the modulator signal. By focusing on the most important elements of speech necessary for understanding, the vocoder encoded speech efficiently, yielding a low bandwidth for transmission. The resulting voice heard at the other end of the transmission didn’t have the complex frequency components of a real human voice, but enough information was there for the words to be intelligible.
Today’s vocoders, used in popular music, combine voice and instruments to make the instrument sound as if it’s speaking, or conversely, to make a voice have a robotic or “techno” sound. The concept is still the same, however. Harmonically-rich instrumental music serves as the carrier, and a singer’s voice serves as the modulator. An example of a software vocoder plug-in is shown in Figure 7.10.
