Please explain the working of circuit mentioned here

 

the Author explained it perfectly fine to me,it transmits audio via an Infra red led tx and rx modules, without a carrier wave.

circuit here...

http://s1063.photobucket.com/user/lookingfordbn/media/infrared_zps430c8bf9.png.html

 

The circuit designer has posted a very detailed explanation on all the components of the circuit: http://www.techlib.com/area_50/infrasound.htm

 

i cant find anything in the link..i want to know the use of each component and how the values are chosen