In my parish we chant the psalm between the OT and NT readings on Sunday for Holy Eucharist. The choir does it in 4 parts. Since I'm in the choir, I'm not sure what exactly the congregation is doing, but I think they chant the "melody" (soprano part). We do distribute the chant notation in all 4 parts to the entire congregation.
The subversives in the congregation (like my family) are changing round the other 3 parts and annoying their neighbors. :-D