Chapter 4 of the HornFX Encyclopedia focuses on two of the effects that are most widely used by horn players: Wah Pedals and Envelope Filter. These vocally expressive pedals evoke sounds of the past but are ubiquitous in the modern as well. They can be hard to handle, and a difficult task to master, but this chapter will give you all you need to make these pedals a meaningful part of your effects set up.