We need to know more about your render settings. The type of compression depends on the codec you are using to render.
if you are rendering for the web I would suggest using the Adobe Media Encoder and one of the standard H.264 presets like YouTube HD.
if you are rendering something like QuickTime with JPEG compression them your audio settings should be linear PCM 48 kHz.
There is a lot of help available on rendering by simply typing rendering in the search help field at the top right corner of AE. Here's the first link that you will get when you do that: After Effects Help | Basics of rendering and exporting