apparently very seperated, steve claims that he would only let him hit one drum for each take on some tracks, recording each in complete isolation, he used one of the first digital delays (can't remember the name) at a very fast rate so that it didn't really repeat but altered the tone of the sound due to the phasing effect, I should think he'll have compressed them to buggery and added other effects too.
Have a read of who killed martin hannett for a bit of an insight, but how true some of that is is very debatable, due to being written by someone who was off his face most of the time, as was hanett himself, if he was still alive I doubt he could tell you what he did, but I'm sure others on here could tell you a lot more than I can.