FaceTime calls lower system volume

When you enter a FaceTime call in OS X, as of Mavericks, it lowers the volume of everything else besides the call. There's no way to disable this "feature." People here suggested disabling audio ducking in Voiceover Utility, but that doesn't have any effect, at least not in Yosemite.

Any suggestions for a hack solution to fix this? I don't want to install some system-wide audio mixer to help, but I'll happily mess with the FaceTime application or some system settings. I'm guessing there's some library it's using to control the system volume, and I'm trying to find a way to prevent the app bundle from accessing it.

Open FaceTime app (don't make the call yet), Paste the following line in to terminal,

printf "p *(char*)(void(*)())AudioDeviceDuck=0xc3\nq" | lldb -n FaceTime

and then make the call.

Update: for macOS sierra or higher, replace FaceTime with avconferenced.

On current macOS (Mojave and Catalina), System Integrity Protection doesn’t allow modifying the running FaceTime app. You will need to route the audio to another app to remove the ducking or amplify it.

One tool is called Loopback app from Rogue Amoeba. In FaceTime app, pick Loopback virtual device as the output so you can get control of the volume.

I am not affiliated with the developer, just a happy user who can't believe how useful this audio app is.