Ok, some of this is hard to express in writing, as its really a how your individual body works... but here goes.
1) I think there were some subtle effects added to my vocals in post processing, (such as slight reverb) however, during most of the song, there are two tracks of my vocals running on top of one another. This is an excerpt from a post Dave O. made about the vocals: Vocals on "The Art of Death Infernal" are pretty much double tracked all the way through. First track down the center, second track duplicated to 2 tracks, paned hard L and hard R and one shifted -10ms and the other 10ms, and mixed about 5 or 6 db under the center track. Handy little trick I use all the time. Works really well with vocals and you don't run into phase problems. Thats all I know about the recording for sure, if you need to know more, just email Dave.
2) This is the part that may become unclear, as Im trying to explain how I feel while doing the vocals. So bear with me. As far as grunting, all of my vocals are done from the vocal chords. When going lower, for the more guttural sound, it takes tons more air for me, so it is tough to sustain for a long time w/o a breath. My throat rumbles when I do this, I can feel a vibration from the chords and lower down my body. When I do the Hear the whispers type rasp, I only feel vibrations from the chords up into my mouth and nasal cavity. Whenever I do any type of vocals though, I need to be well lubricated. Water and milk do very well in that regard.
For the other stuff, if youre a singer, like in choir and stuff, its really a carryover to get the sounds youre looking for. To get rid of the bumpy grumbly sound, it really depends on your breath support. You have to push air out from your stomach by tightening your diaphragm. The closest thing I can think of doing that is tensing your abdomen muscle, thats what it should feel like whenever youre letting air out. For the grainier sound, that is really the lubrication doing its job. If my throat is dry, I can hardly get anything to sound decent.
For that last bit, I get sore throats if I start heavy rehearsals, like leading up to the recording, we were playing 3-4 hours a day, which really got me sore quick. If I go that long without doing it for a period of time, I lose my voice completely for a couple hours. But every day you do it, you get less and less of a sore throat. Like when were done for the day, and Im pretty much unable to speak, I just drink something, and dont speak for the next hour. Then by the next day, Im all ready to go.
Hope it all makes sense, and good luck with your vocals.
....Goddamn, I just wrote a novel.