I used mass-loaded vinyl on a separate stud wall in front of the brick wall, with gap all round to break transmission paths from wall/floor/ceiling, then sealed with fire-proof mastic (not for fire-proofing, but as an acoustic mastic, then two staggered layers of
15mm plasterboard hung on resilient bars.It did make a good difference for one room, but I decided too much hassle to do for all rooms on the party wall, I considered a layer of sand-filled triple flute AAA corrugated cardboard for other rooms, but I know I'll be leaving eventually, so not as bothered to do anything about neighbour noise as I once was ... SEP.