Subchannel coding The transmission of auxiliary data on CD data frame subchannel bits. The addition together of multiple signals. Mathematically, the superposition principle characterizes linear systems. All this put into a single formula gives the superposition principle. It is usually applied backwards when we already know the system obeys linearity.
Transform coding is a special case of subband coding.
Vocoding The superimposition of the estimated varying short term spectral envelope of a signal on another. Used as an effect to create illusions of singing instruments and other spectral hybrids of separate sound sources.