^ I think he meant Bale, not Keaton (maybe that was a typo on your part too).
It seemed pretty apparent to me that his voice had some sort of modulation in TDK but I don't think he had it in either of the other movies; definitely not BB anyway.
Yeah, Bale's voice in TDK and TDKR definitely sounded electronically altered to me; of course he was doing the growl himself, but it was further enhanced to sound deeper.
I think they'll almost have to electronically alter Affleck's voice as well. Because it's just way too high and light for Batman, and I can't see him being able to deepen it much on his own.
Unless he starts smoking 20 packs a day before now and then or something.