13. Effects and Spatial Audio

In this chapter, we study audio effects: processes that transform a sound, usually for creative purposes in sound design and music production. Formally, effects are filters, in the broad sense of Chapter 9: functions that map input audio \(\mathbf{x} \in \mathbb{R}^N\) to output audio \(\mathbf{y} \in \mathbb{R}^N\). But when we say “effect”, we usually mean a filter that is either (1) not LTI, or (2) LTI, but built from simpler filters arranged in more sophisticated topologies.

Effects are built from different signal processing techniques, some of which we’ve already studied, and some of which we have not. In each section of this chapter, we will examine one of these techniques from a technical perspective, and also explore the family of creative effects it gives rise to.

In the last section of this chapter, we study spatial audio: combining multichannel digital audio with playback over multiple loudspeakers, to preserve the cues that we use to locate sound sources in space.