Does HDMI carry digital video and digital audio simultaneously, or do I need a separate digital audio cable?

PoohBear is incorrect. HDMI will pass a video and audio signal. If you only have a tv and dvd player, then plug the hdmi cable from the dvd player right into the tv. It will display the video signal as well as playback the audio signal into your tv's built-in speakers. If you have a receiver and surround sound in the mix, it gets a little more complicated. Run the hdmi cable from your dvd player into the receivers hdmi input (this will deliver video and audio signals to the receiver). From here, the audio will be played back to your surround sound that you have connected to your receiver, so the audio part is done. As for video, that signal still needs to get to your tv! If your receiver has an hdmi output, connect an hdmi cable to the receiver's hdmi output and into your hdtv's hdmi input. If your receiver does NOT have an hdmi output, then you must utilize your receivers component output (every receiver should have this). Connect some component cables to your receiver's component output, and plug the other end into your hdtv's component input. The hdmi cable from your dvd player passes the audio and video signal to the receiver, plays the audio, and passes the video signal through component cables to your hdtv. Hope that helps!

Poohbear and mandimil are not correct. If your AV Receiver has an HDMI input, it will also have an HDMI output and will be programmable to accept the digital audio over this connection as well, and pass on the video over to the TV. In some installations we have used two connections, but generally the simplest and best way is to hookup your sources to the receiver with 1 hdmi, and then to your TV with an HDMI and thats it!

An HDMI cable carries BOTH audio and video you do NOT need a separate cable. Now this assumes you are going from the DVD directly to the TV and not through a surround system or other device, and the DVD and TV both have HDMI ports.

HDMI carries both audio and video. But there are 2 ways to wire things up: A: DVD player -> AV Receiver -> TV (HDMI, and HDMI) B: DVD player -> TV -> AV Receiver (HDMI and digital) This second hookup is where you use HDMI from the DVD player to the TV, but you run digital audio from the TV OUTPUT to the AV Receiver. With hookup "B", you use the TV speakers for casual watching, but turn them down and fire up the AV Receiver for more serious movie watching.

The answer to both of your questions is...yes. And it's confusing. While HDMI can carry both signals, your receiver isn't able to separate out the audio signal. It can only pass the entire signal through to your TV. This means you still have to connect a digital coax or optical audio cable to the receiver in order to get surround sound.

HDMI cables carry BOTH digital video and digital audio, so a separate source is not needed.

One note! If you use an adapter, such as a DVI to HDMI, one a HDMI cable, then you would need audio cables also.