After installing WavTap the volume of my MacBook dropped considerably.
I found out that WavTap set itself as the Output Device and by setting it manually back to "internal speakers" my volume was correct again.
After that setting it back to WavTap fixed the volume level of my speakers and I could enjoy WavTap :)
Yeah, this is a design flaw.
Ideally, WavTap would just tap into the outgoing audio stream of the system's preexisting output device. Outside of relying on something like JACK or SoundFlower, this is straight-up not possible with existing CoreAudio APIs (It would be really really really awesome if someone could tell me I'm wrong about this), so WavTap has to do a lot of behind-the-scenes hacks to make it seem like this is what's happening.
In particular, WavTap needs to respond to system volume changes. Initially, this is the algorithm I chose:
This approach has one benefit. Namely, WavTap can quit or crash without worrying about modifying the preexisting audio device's volume settings. But there's one major problem: WavTap can never get louder than your system was when you launched it.
A better design for this whole procedure is a really high priority right now, and I'm open to suggestions!