I am working with audio in the iPhone OS and am a bit confused.

I am currently getting input from my audio buffer in the form of pcm values ranging from 
-32767 to 32768. I am hoping to perform a dbSPL conversion using the formula 20LOG10(p/pref).

I am aware that pRef is .00002 pascals, and would like to convert the pcm values to pascals.

My question is 
 a) what are these pcm values representing exactly.
 b) how do I turn these values to pascals.

Thanks so much