Information regarding audio support
Audio output over HDMI is only supported when the graphics card of the notebook or desktop computer supports audio output over DisplayPort. Several on-board graphics adapters such as Mobile Intel 4 Series Express Chipset in Notebooks (i.e. Dell E6400) do NOT support audio output over DisplayPort, even when HDMI support (Intel High Definition Audio HDMI Service) is installed for audio controllers. In such instances a separate audio connection has to be set up.
What is "DisplayPort"?
DisplayPort is a digital video interface connection designed as a replacement for the DVI standard currently in use on computer hardware. It is similar in specification to the HDMI standard, but unlike HDMI, DisplayPort is being targeted as a computer interface rather than a home theatre interface. DisplayPort differs from VGA in that VGA is analogue and DisplayPort is digital.