Thank you all for the very informative replies. I will install the latest Mame32 on my wife's Windows XP laptop (EW!
) and listen to the thumps.
My take on the pitches comes from my musical background. My father is a music professor at a California State University. I grew up with a piano and lessons in various instruments. I remember playing the thumps on my piano! LOL... ...and even reproducing many of the sounds on one of the analog synthesizers at the college's music department. (Fairly accurately if I do say so myself.)
I can say with almost absolute certainty that the interval between the thumps was a minor second (A half-step on a piano keyboard) on every Asteroids game I ever played... and I played every single one my parents let me. :-) As a kid I was always fascinated by the quality of certain intervals. Most doorbells are either a major third or a minor third. I like the one at our house because it was a major third; it's happier sounding. Minor thirds are morose and troubled. (I know... I'm a weirdo.) I distinctly remember taking note of the minor second interval in Asteroids and being fascinated by the nerve-wracking suspense it induced. The major third interval in MAME's Asteroids is like a happy doorbell; it just doesn't fit at all.
I don't know what the Asteroids thump notes actually were. (I'm not lucky enough to have perfect pitch.) But when I hear the Vectorama samples, that nails it better than anything I've ever heard anywhere else.
It also seems like to me that MAME's Asteroid sounds are much warmer than that of the real game. The arcade cabinet blurted out harsh square and sawtooth waves. That edgy, stabbing quality seems somewhat smoothed out in emulation.
I shall take the advice of R. Belmont and cross post my original post to MAMETesters.org and see what folks have to say. I'll report back any interesting progress. I wonder if my musical sensibilities would carry any weight when the schematics seem to tell a different story.