Straight from my notes, a direct comparison between the Emerald and Black Dog:
Emerald
I characterized the Emerald as being 'Chimey'; There is a very strong midrange presence, but also a lot of upper mids and treble. In the neck position, the Emerald has a midrange scoop and bit more on the frequency extremes.
With the gain turned up, the Emerald balances out a bit more, and the midrange, while still abundant, is a bit more balanced by all the harmonics and overtones you get when you have more gain.
Black Dog
I characterized the Black Dog as being 'Brighter'; There is actually less midrange in the Black Dog (to my ears), but also less bass and lower mids, which give the Black Dog more cut and presence. No matter what position you put the Black Dog in, it retains the high frequencies intact.
With the gain turned up, the Black Dog rolls off just a bit of the highest frequencies and lower mids. This gives the Black Dog a screaming lead tone with high gain.
