I have been wondering this for a long time.
How about using the genuine article, a microphone and a volunteer from the audience?
I believe Matt Groening once said in an interview that very early in the show’s existence (maybe during the Tracey Ullman shorts) they needed the sound of a pacifier and after trying a couple of options, he stuck a real pacifier in his own mouth and sucked. And they’ve used that sound ever since.
The audience? I imagine if the Simpsons were filmed in front of a live audience the animators’ wrists would get really tired really fast.
Didn’t think it necessary to conclude with a smilie…
I prefer my forum conversations free of the smilies. When you stop using them the discussion gets much more vague and amusing. Sarcasm works best when the victim doesn’t recognize it.
According to the Maggie File at http://www.snpp.com, the sucking sound is variously credited to both Gabor Csupo (of Clasky/Csupo Animation) and Liz Georges. Yeardley Smith makes all the other baby noises, like crying and cooing. Matt Groening probably did NOT provide the pacifier noise.
As to how they did, they just stuck a pacifier in their mouth and sucked.
My sentiments exactly;)