The scream
detector is a simple amplitude detection
program running on one of the SGI Indy
workstations. There is a single microphone
placed in the room between the screens that
is monitored for a few seconds at the
appropriate time. If the loudness of the
scream goes above a set threshold, the
control program accepts the scream and moves
on in the story.
If the scream
is below the threshold, the narration
encourages the children to scream a second
time. If they fail to achieve this second,
slightly easier, threshold, then the
narration lets them know that it wasn't a
very loud scream but that they can continue
anyway (e.g. "Well I can't say that
was a very loud shout, but perhaps the
monster will figure it out!")
The effect is that when the
children yell loudly, they get immediate
positive feedback from the system, but when
they fail to yell, the system acknowledges
that it knows they didn't yell loudly but
keeps the story moving.