Charlie, If I understand the OP right, they are looking for a way to adjust the volume for sounds on a per app basis. Right now for example, I'm listening to public radio using Safari but if I am editing something in QuickTime Player X the sound from one thing will overpower the other.
@Kylebrod I am currently testing an app called
Sound Control that seems like it will do what you want to do. Just started looking at it so I haven't mastered the features but it looks promising. There is also a similar app called VolumeMixer which was discussed
here.
I'm pretty sure thatAudio Hijack Pro could be configured to do this as well but it is more expensive than either of these programs. TBH I find the current interface for Audio Hijack Pro a bit confusing and annoying so I haven't tried it to much with that program.
I'm not sure how well these programs would work with FaceTime since it seems ro be designed to lower the volume of other programs when a call comes in.