Comment 27 for bug 871582

http://www.intel.com/support/motherboards/desktop/sb/CS-020642.htm

How to identify your front panel audio solution codec
To identify your front panel audio solution’s audio codec, refer to the specifications or documentation for your PC chassis or front panel module. Note that AC’97 and HD Audio front panel solutions are different and may
not be directly compatible or interchangeable.

You can also physically check the audio cable of the front panel audio solution. If there is a cable connected to Pin 4, you have an HD Audio module; if there is no cable to Pin 4, you have an AC97 module.