ABSTRACT
This chapter introduces several audio effects based on a signal's amplitude envelope. A signal's amplitude envelope is the overall gross shape of how amplitude changes over time. In some cases, the amplitude envelope is referred to as the temporal envelope to specifically distinguish it from a spectral envelope or curve. There are several different audio effects based on the amplitude envelope. All types of envelope-follower effects are based on extracting the amplitude envelope from one signal and applying it to something else–ranging from another signal's amplitude, to a filter's cutoff frequency to a reverb's time. The process of applying the attack, decay, sustain, and release (ADSR) amplitude envelope to the carrier signal during synthesis is based on the element-wise multiplication operation. The vocoder is an envelope-follower effect that uses amplitude modulation. This effect extends the process of measuring and applying an amplitude envelope to multiple frequency regions of a signal.
