HDMI cable connected from new HP Spectre i5, 4Gb, 128Meg, (WIN 8.1) to TV, picture fine but no sound

Hi.. HP spectre G4X24PA#ABG, bought a few days ago, links in via HDMI cable to Sony HD TV - picture fine but no sound.. tried Control Panel, Sound etc but no HDMI sound to click and make say default??   IDT High Definition Audio Codec listed but no connect to HDMI - suspect drivers not up-to-date?? But HP assistant says all is up to date??  Have looked on web - many answers for Win XP/Vista etc but I am running WIN 8.1- can always connect external speakers or use Y-connector but I think this single HDMI cable SHOULD work?? Any help much appreciated - first post so please treat me gentle  (and as a new silly nerd head please... i.e simple replies please...)!!