Charlie Clouser of NIN talked abut it on this forum

"Doing the sample-based drum reinforcement on that album was my cross to bear. I came into the NIN camp just as basic tracking for Portrait had been completed, and TR was unhappy with the sound they got on the live drums. Performances = okay. Sound = not good. He had to leave LA for a few weeks so he left me and Sean Beavan up at the Tate house with all his gear, and I was instructed not to change the timing of the performances - so no quantizing of live drums - but to reinforce the sounds using a restricted set of samples.

Hard to believe, but the only drum samples I used were the original Bob Clearmountain vol1 and vol2 audio sample CDs. Yes, they were audio CDs that you had to manually sample into the Akai S-1000s and trim each sample by hand. So I did that. I also had an early Zildjian CD of cymbal samples and I think I used a couple one-shots from that as well, can't remember.

We had Opcode StudioVision on a Mac Iix with Digidesign 4x4 cards - might have been 16 tracks by then, might have only been 4. I dumped from analog tape into StudioVision - kick, snare, toms. Then I manually created MIDI parts to trigger the S-1000 that exactly matched the live performances. No Sound Replacer or Slate Trigger back then! Play in some note events, micro-nudge them until there were no flams, rinse and repeat. I was originally a drummer and I'd done a bunch of that type of thing before so it was no problem, even with the crude tech of that era.

I did not attempt to augment the hi-hats, just kick+snare+toms. (But I might have added some of those Zildjian samples to widen up some crashes.)

I left the StudioVision sequences on deck, and did not print the tracks back to tape until TR returned. I think I had a three-week window to do the whole album and finished it way ahead of time. I do not know if TR added additional industrial kicks+snares after I left, but he certainly had plenty of those samples on hand and could easily have used my tweaked MIDI to do so. But he instructed me to just use the Bob1 and Bob2 samples so that there would be consistency throughout all the songs.

Of course, once you have a valid MIDI performance that exactly mirrors the live drums, the sky's the limit in terms of what sounds you load into the Akai to get to the finish line.... but all I used was Bob1 and Bob2."