Sound-proofing requires you to build structure within structure - you build a room inside a room. This is done so that there is no acoustic linkage between the inner and outer structures, as most noise that escapes from a room does so via structurally-borne routes.
Double glazing (inner and outer panes of glass or even triple glazing) are a must if you have to have windows that connect outside.
Treatment, on the other hand, is about reducing reflections (and therefore room borne reverb) and absorbing freqs related to the resonant dimensions of the room. These resonances can be reduced or even eliminated with the correct design of internal structure to ensure that no two parallel surfaces are allowed to face each. Putting in absorbers can actually serve to break up otherwise parallel surfaces.
consider the following:
the black is the outer shell
the red are angled side walls about 12[sup]o[/sup] from back to front
the blue is bass traps set at the front of the room
the green is angled rear walls about 6[sup]o[/sup]
as a direct result of this design there are no parallel surfaces within the room itself. Add a sloped ceiling and you eliminate the last possible source of parallel surfaces - a room that then only needs absorbers and diffusers added at strategic points to capture first reflection points