Go and get the data sheet for the STAC9708 AC'97 Codec @: http://extranet.sigmatel.com/ library/audio/stac9708/stac9708-ds.pdf Check out pg# 33. It appears register 0x6Eh, bit D2, enables 4-Speaker playback of 2- Channel content. reg = (0x6e << 16) | 0x4 I think he is bit ORing D2 so it will be high Much thanks for the code :)