Mining the 'Or' in the Digital Cable Order

Somewhere out there, you might not have noticed that audio exists. This is especially true if you are a producer, director, member of the lighting persuasion, or camera op.

"There's a microphone in the shot!" is a common cry on set (or in studio). So is "boom shadow!" As everyone (except those weird audio folks) knows, sound is supposed to be magically picked up without apparatus, even if the sound is coming from the center of a circle of working cement mixers, where someone whispering is being shot at the tight end of a 101x zoom lens.

On account of everyone knowing that, I ain't going to beat that dead horse noiselessly in this month's rant. No, I'm just going to briefly mention someplace where folks usually do take note of sound or absence thereof. Yes, I mean home TV sets.

Back in the days when video and audio traveled separate network paths, if the video got lost, it was replaced locally by a "Please Stand By" slide, and the show went on. If the sound took a detour, the show was over. Folks at home notice an absence of audio. That's what was so strange about the Sept. 10 digital-cable order from Our Beloved Commish (aka the FCC).

Well, now, okay, a whole heck of a lot of the order was pretty strange. But this lunar cycle I'm going to limit myself to this here paragraph from the news release (this being the computer age, the full order ain't yet been released as I write this in October 2003):

"High-definition set-top boxes-starting April 1, 2004, cable operators must supply, upon request, high-definition set-top boxes with functional 1394 'FireWire' connectors. By July 1, 2005, all high-definition set-top boxes would also require a digital visual interface ('DVI') or a high definition multimedia interface ('HDMI')."

Never mind that IEEE-1394 connections come in 4- , 6-, and 9-pin copper versions and even others using existing or planned plastic or glass fiber. Never mind that they come in data rates from a wee mite less than 100 Mbps right up to 3.2 Gbps.

It's okay to never mind that stuff on account of there are cheap (and readily available) adapter cables that go between the different pin counts. And, as far as set-top boxes are concerned, the 1394 flavor of interest is S100, the under-100 Mbps version, which is the copper variety. So, starting April 1 of next year, things are okay.

It's the "or" in the July 1, 2005 sentence that's maybe just a wee, tiny, infinitesimal problem-if you happen to be one of those weirdos who like to hear TV as well as watch it. DVI absolutely ain't the same thing as HDMI.

Where did Our Beloved Commish get the idea that it was? Well, now, one likely source was the cable/consumer-electronics (CE) agreement submitted last December. It says there have to be "DVI or HDMI interfaces with HDCP [high-bandwidth digital content protection](CE manufacturer's choice."

As for where the cable and CE folks got the idea that DVI and HDMI are equivalent, it might have come from this part of the FAQ section of the HDMI Web site:

"Is HDMI backward-compatible with DVI (Digital Visual Interface)?

"Yes, HDMI is fully backward-compatible with DVI using the CEA-861 profile for DTVs. HDMI DTVs will display video received from existing DVI-equipped products, and DVI-equipped TVs will display video from HDMI sources."

That first sentence might be actionable (litigators, please send me my cut in care of this magazine), but the second ain't so bad. Do you see the words "sound" or "audio" there? Me, neither.


Here's the deal. Way, way, way back in the ancient days of 1998, the Digital Display Working Group was formed to simplify connections between computers and monitors. A year later, in April 1999 (two whole years after Our Beloved Commish published its digital television rules), the first DVI spec was released.

It's pretty cool. It uses transition-minimized differential signaling (TMDS) to handle clock rates as high as 330 MHz. It'll easily do SXGA (1280 x 1024) at up to 85 Hz refresh or UXGA (1600 x 1200) at up to 60 Hz refresh.

It's got a connector relatively hefty in this age of sub-sub-sub-notebook computers -- a jack about 37 mm wide and 10 mm high. In the DVI-D version, the connector has three rows of eight contacts each. In the DVI-I version, another five contacts are added to handle analog RGB with H and V sync. The DVI-A version has just the five analog contacts. Then there was DVI-CE.

Remember those digital television rules? Remember those sub-sub-sub-notebooks? So the idea was to create a smaller DVI connector for tiny computers and consumer-electronics products. It'd still use TMDS, but it'd add bells and whistles.

So, way, way back in April 2002 (five years after the rules came out), the HDMI working group was formed. Sure enough, they came up with a smaller connector-19 pins in a plug just 13.9 x 4.45 mm-but they had to give up the 330 MHz clock rate to do so, dropping to 165 MHz.

That is, they gave up 330 MHz in the 19-pin Type A HDMI connection. There's also a 29-pin 21.2- x 4.45-mm Type B HDMI connection, which is allowed to go to 330 MHz clock and transmit video in ways the Type A ain't.

You think ATSC A/53 Annex A Table 3 is complicated? You should read the HDMI list of video formats. It includes 2880 x 240p and 2880 x 288p, of course, but it doesn't include ordinary interlaced 480i or 576i. It also doesn't include such traditional cable and satellite favorites as 544 or 352 horizontal.

Hey-that's just video (which can be carried at up to 5 Gbps, by the way, so no worries about 1080p even at 60 fps). The real beauty of HDMI is that it also includes for remote controls and-ready, now?-up to eight channels of digital audio, which may go as high as 192 kHz sampling each.


So think about what that does at home. Suppose you've got an HDTV with built-in (could be infrared-connected) 5.1 channel sound system. You used to connect maybe three cables for component video and another six for sound, all analog. One HDMI takes care of the whole thing, lets your TV tell your set-top box what aspect ratio it ought to send, and also carries remote-control instructions from the TV back to the box. Nifty keen-o, eh?

That's if you've got a 19-pin HDMI connector on the box and a 19-pin HDMI connector on the TV. If you've got a 19-pin HDMI connector on the TV and a 29-pin HDMI connector on the box, maybe someone will make an adapter by July 1, 2005; there surely ain't any around now.

If you've got a 19-pin HDMI connector on the box and a 24-pin DVI connector on the TV, you'll need an adapter for that, too. Lo and behold (methinks "lo" is short for "look," but that would be redundant), Molex actually already makes the necessary adapter cable.

So, just as the HDMI FAQ says, "HDMI DTVs will display video received from existing DVI-equipped products, and DVI-equipped TVs will display video from HDMI sources." That's video. What about the audio?

If the box has only an HDMI connector for the audio (and, why not? -- it takes up a lot less space than nine RCA jacks), then your HDTV can display beautiful, digital HDTV pictures and deliver no sound at all. HDMI carries eight channels of digital audio. When it comes to audio, DVI carries zilch.

Yet, according to Our Beloved Commish, choosing DVI or HDMI is an option. CE manufacturers can choose whether to allow viewers to hear programs or not. Either. Or. Else.