So you can make a video layer in After Effects to show the audio spectrum of an audio layer, which displays the magnitude of audio levels at frequencies in a chosen range. I was wondering if there is any way to get the raw information used to create this video layer and export it, say to a csv file.
So to make it clear, the csv file would contain values for the amplitude/energy in each frequency range at different times.
Straight answer: That's what audio processing tools are for. You are completely looking in the wrong place if you plan on exporting statistical data for frequency bands, energy plots or whatever from AE, given that it is probably the most unsuitable tool for audio processing in the first place...
The only option you have is to convert audio to keyframes and then copy all keyframes and paste them into a spreadsheet. That would give you amplitude only. As Mylenium suggested, AE has very limited audio tools and there are much better apps for your project.