How to analyse audio and to affect source?
I have actually just finished a project doing exactly that. I used a frequency analyser chip called an MSGEQ7 (Available from Sparksfun), here's the datasheet.

https://www.sparkfun.com/datasheets/Components/General/MSGEQ7.pdf

These little things are really easy to use. Give me a shout if you would like any help with it such as coding or wiring.