Played when the UFO ship appears at the top of the screen.
This circuit uses a common and well documented chip. Actually, I have found this exact configuration in a couple of magazines associated to "siren" effects and it is also described in the SN76477 datasheet for a siren, space war or phasor gun sound.
MAME already emulates this chip, Tickle will in the close future.
Copyright (c) 2004 Alessandro Scotti. All rights reserved.