gnaural - 2014-01-10

Your question:

Example: If I wanted 12hz, would I make the beat frequency 212hz
and the base frequency 200hz? (60,40; 122,102; etc.)

No. You'd make the Beat Frequency 12hz and the Base Frequency to whatever you want.

In other words, the only parameter you need to set to achieve 12hz is the Beat Frequency. So long as the Base Frequency is in a comfortably audible range (say 100hz to 400hz), the 12hz Beat Frequency can be effectively imposed over the Base Frequency. You don't need to do any math to get the left and right channels to do the proper Beat Frequency, simply set the Beat Frequency itself.