It's all relative, we have to take into account the type of noise emitting source and the proximity between emitter and receiver. The bothersome noise factor also varies from one geographical area to another. For the most silent places with the least tolerant legislation, noise allowed in the permeability of walls or insulation is 3dB above environmental noise. However, if the idea is to make music or play an instrument inside an apartment, you should know that this is not allowed. You'll have to find a compromising solution and count on your neighbour's understanding.