I would guess that in poltergeist, the way the little
girl starts is actually a sample of her backwards,
put through a delay. When the words start becoming
clear (Help me) I would assume its her speaking forward,
with a delay and harmonizer, and I think a few mens
voices are thrown in there as well.
Its funny, because once you reminded me of that, I can hear
her voice and effects very vividly. It has to start
backwards, that makes sense. She is probably
recorded many times, and the starting points are
staggered.
Just my guess. If they didnt do it that way, I bet
one COULD do it that way and get the same effect.
Of course they used every flanger, reverb, phase
trick ever invented too.
Cheers David