You can think of a vocoder as a morphing multiband equalizer, in which the morphing is controlled by a spectral analyzer. Typically, speech (called the modulator) is analyzed and matching equalization is applied to a pitched, harmonically rich source (called the carrier). Lightning-fast personal computers have allowed the quality of analysis and the number of bands to increase radically, and the uses for vocoding have expanded accordingly. In this column, I'll discuss an unusual approach to vocoding that has broad application: using the same signal as modulator and carrier.
