STOP THE ROUNDABOUT WE ARE GOING IN CIRCLES HERE!
EDIT: Look, the point I was making is that their voices are squeaky, VERY squeaky. Maybe that is an effect of radio transmition underwater, but I doubt it, since I can find no evidence of it. You say that they would not be using helium at that depth.... and I don't WANT to disbelieve you, but there is no other gas that can safely be inhaled in any amount by humans that has the right density to produce the squeak.
So, if helium is not making them have squeaky voices: WHAT is?
