Audio power intensity filtering

I have spent many weeks working on this project with no luck, any help in the right direction would be greatly appreciated. My lack of Matlab knowledge is defiantly the issue. 1. I am trying to input a wav file into matlab and find the power of the signal. 2. After I have the power across the signal I want to use the following equation: sound intensity = sound power / (4 pi R2) to receive the sound intensity across my signal. 3. Then finally filer any intensity levels that are above the same hearing limit. While keeping the lower ones the same. I have received a hint from my professor to use automatic gain control however I do not know how to implement it into matlab. Thank you in advance for any help.