A series of quick reference tables showing the main specs of the most popular audio codecs you can find on motherboards. Check it out at HardwareSecrets.
"Audio codec is a small chip measuring 0.25 sq. in. (7 mm2) located on the motherboard in charge of the analog audio functions. Knowing the specs of a codec will permit you to compare the audio quality of different motherboards, allowing you to choose the right product for your needs."