Perceptual Coding

I've done some research into how spotify compresses their audio for delivery to listeners. It seems that they use AAC and OGG Vorbis. I dont think that in my paper, I will go into depth regarding these specific algorithms, but instead outline what perceptual coding is.
This section will have to be smaller, because I could write pages and pages regarding perceptual coding, but I have so much other stuff to cover.