great picture but no sound


picked up a playstation 3 today, hooked er up, got the video, but no audio....using hdmi for video and the av cable for the audio...i set the audio up in the menu for the av...i'm sure i should be using a better audio cable, but isn't the av the right one until i order something else...am i missing something in the menu....thanks for your help, brent
128x128knollbrent