They have great bass but are also slightly trebly

the 770's have a much clearer sub-bass/bass signature with a slightly less clear mid range and high range

The bass is always clear without sounding boomy, the high are smooth and present.

These headphones to do not overemphasize the bass or treble and just give you an extremely accurate reproduction of the audio track you are listening to or working on

Incredible bass

I own the Dt 990 pro's as well, and comparing the two, it seems like the 990's are more clear mids and highs with muddied and violent bass/sub-bass

I used to have a pair of Sennheiser headphones I used when mixing and they were a bit bass heavy and led my tracks to a bit too much bass at times when replaying on other speakers or headphones

Amazing sub-bass and incredibly good soundstage for closed back headphones