Also posted this at avsforum:

Am I mistaken, or can audio travel through HDMI-DVI cables?

I'm watching a DVD and audio is coming through the TV speakers, but the TV is connected with an HDMI-DVI cable.

(The DVD player is hooked up to the 990 via HDMI-DVI and the 990 is hooked up to the tv via DVI-HDMI Video 6. The only other cable hooked up to the TV is a component cable to Video 4 from the pre/pro which I use for by XBOX 360. )

I thought this was impossible?

I didn't think that it was possible, either (there was actually a discussion of that here a while back). I guess that to be certain, though, I'd have to dissect a DVI-HDMI cable. The question in my mind is whether some of the HDMI conductors are abandoned at the DVI connector or whether all of them find a home in the DVI pins. If they all get carried over to the DVI connector, then the audio signal could be passed through the 990 and on to the TV.

A little poking around in google may give us some hints. HDMI has 19 pins (the type B connector that would be needed to handle higher resolutions will use 29 pins, but I don't think it's actually in use yet since it's only needed to support resolutions above 1080p). It is also pin-compatible with single-link DVI (meaning that if we connect the right pins of the HDMI connector to the right pins of the single-link DVI connector, we get video - and type B HDMI is pin-compatible with dual-link DVI). The 990's DVI video switching supports a dual-link DVI connection, I believe (at least it appears to have conductors in place for the dual-link portion of the connector). Dual-link has 24 pins, five more than the total pin complement of HDMI. I guess that it would be possible for two identically-made cables that used DVI-D dual-link connectors and kicked the HDMI audio signals to the same extra pins provided by dual-link, which would then allow the audio signal to pass through the 990's DVI switching.

Well Gonk, I don't know...

To be honest, I don't 100% understand all of the technical jargon. I can tell you this, though, I am not using dual link cables. I am actually using Blue Jeans Cables found here. (not the dual link style)

I have the same cables from my Cable Box to the 990 yet no audio gets through this way. This points me to the DVD player. There are some HDMI audio settings on the DVD player that I glanced over during initial setup(pretty much ignored them, though, as I thought audio would be lost in my HDMI-DVI conversion).

I'll take another look at those settings when I get home...

Cheers.

Dual link only applies to DVI-to-DVI cables. I can't tell for sure from the picture at Blue Jeans, but I think the DVI connector on their HDMI-to-DVI cable may be single link (which would kill my initial theory). If you can, look at the DVI connectors on your two cables and see if they have a solid group of 24 pins on the left side (dual link) or if the middle third of that group is missing (single link).

DVI does NOT support audio at all.

Let’s be clear on the difference between the DVI standard and a multi-pin data switcher that happens to use DVI connectors. The DVI standard does not support audio, however, if a piece of equipment has the ability to switch between data input via multi-pin cables and connectors, pin-for-pin for all pins available, then it can pass any kind of data through those pins – ANY kind of data that requires no more than the number of pins available and does not exceed the capability of the electronics. The 990 does not decode incoming data, whether DVI data or HDMI data arriving via a DVI connnector, nor encode data for output, it merely passes through the data being input, therefore the standard or format or content of the data does not matter. As such, if there are enough pins to carry HDMI data, including audio data, through the DVI connectors, then that data passes through as easily as any other data. Simple.

bestband4thebuck.....i'm not afraid to say...I had to go and get a glass of Cognac after reading that. So like many of us who have the 990 (DVI Out); and have probably chosen to go DVI to HDMI, how is the audio information from the projector translated at the processor if no audio info is there? Does my question make sense?

What bestbang4thebuck's saying is that it is theoretically possible for the audio portion of an HDMI cable's signal to pass through the 990's DVI switching, assuming that the two DVI-HDMI cables are terminated the same way and that the audio conductors are terminated to some of the extra pins in DVI's dual-link connector. What does that get you? Not very much, actually - the 990 doesn't actually do anything with DVI input signals (just steers them back out, unaware of the content of those signals), and the HDTV (direct-view, rear projection, or front projection) isn't really going to have much use for the audio once it gets there.

After looking at the pinouts for the two connectors on wikipedia (sorry, too lazy to dig up actual standards and look at those, so I'll trust the masses on this one), it looks like there are no dedicated audio conductors, and the audio data is just sent along with the video over the TMDS channels. If this is really the case, it would seem that for any DVI-HDMI adapter to work properly, it *must* wind up passing HDMI's audio signals.

What I'm not clear on is why this doesn't screw up your picture if you connect an HDMI output to a DVI input on a display. I haven't a clue what format the data actually takes, but one could speculate that maybe there's some packetizing or headers or something that causes a DVI display to discard the audio bits because it doesn't what to do with them? Anyone with more in depth knowledge of HDMI standards, please correct me or back me up or explain...

On further examination, it seems more likely that the DDC channel enables a DVI display to tell the HDMI source that it's just a lowly DVI display, so the HDMI source can go into backwards compatibility mode, whatever that may entail.

Of course, all this is contingent on the assumption that the 990 is "transparent" as far as the display and source are concerned - which seems likely based on what the OP is reporting. In this light, it seems to me that the fact that the 990 doesn't transcode to DVI or offer OSD on DVI is, in fact, a feature