Having taken a two-chapter detour into aspects of control and
organization in electronic music, we return to describing audio
synthesis and processing techniques. So far we have seen
additive and wavetable-based methods. In this chapter we will
introduce three so-called modulation techniques: amplitude
modulation, frequency modulation, and waveshaping. The term
``modulation" refers loosely to any technique that
systematically alters the shape of a waveform by bending its
graph vertically or horizontally. Modulation is widely used for
building synthetic sounds with various families of spectra, for
which we must develop some terminology before getting into the
techniques.