The Wonderful and Sometimes Confusing World of HDMI Connections

[rfowkes]

HDMI (which stands for High Definition Multimedia Interface) was developed to accommodate the emerging HD digital technologies which have now entered the mainstream of home entertainment. It was planned as a "one wire" digital solution to both audio and video requirements. It is also one of the most confusing connection technologies available to the general public - especially when people hdmi(3)are used to more traditional interconnectivity. As HDMI attempts to do what it was designed to do, part of the process involves the pieces of the puzzle communicating with each other (sometimes referred to as "handshaking"). This two way communication causes...

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[Roger Halstead]

HDMI was not designed as a "one wire" solution for us as users. HDMI was designed to implement DRM into one AVI "cable" (It's not one wire) and force the end user into a system using integrated DRM. . Were it not for DRM we'd have no need for HDMI cables and could get along just fine with with equally capable DVI + audio. Those could also easily be combined into one cable and we'd not have to wait for both ends to decide the other is a valid device.

I don't know about others, but I find the wait (even when all works well) to be very annoying. It's even more so when I remember we have this only because "the studios" wanted more layers of content protection with no concern about what used to be called "fair use".

[rfowkes]

O.K. "One Wire" was not meant to be taken literally, but in the contexual sense of a colloquialism. Obviously I realize that these cables contain more than one wire within. This is a question of semantics, not technology. Point taken.

And yes, I also don't like to see the inevitable "wait period" no matter how short, and even when everything is working "properly" by HDMI standards. Any handshaking based system will involve some of this. My main point on this (which I perhaps should have clarified more) is that the average user of such equipment is probably used to the (practically) instantaneous response of a non-HDMI wiring ("cabling") system so that even a short lag time before connection is viewed as a flaw. It's a different topology and sometimes equating it to older models doesn't hold. I agree with your point about wait times being an annoying (read: different) aspect of HDMI. We just need to educate the public that such delays (assuming that they are not too long because of improper implementation) are part of the HDMI scenario. In my opinion, this is something that is often left out and the cause of some concern becasue of its omission.

[olliesam]

Hi. I was reading the Article this morning and found it to be very informative - informative and added another layer of information to my already overloaded brain cells One question I have relates to the 'thickness' of the cable itself. Though possibly not relevant there appears to be a difference in the thickness of the cable and its ability to transmit the signal power from the box to the tv + different strengths depending on whether a 720p or 1080p tv. I purchased a 10.2 gb capable cable as it is supposedly captures the best signal for a 1080p tv. I did NOT purchase an expensive [$100+] cable from one of the large retailers but, rather, a relatively inexpensive one from one of the auction sites. It appears to be working JUST FINE and brings in a beautiful and clear picture [of course, not having any comparisons to it other than my composite cables]. So, regarding the matter of cost - very expensive is not necessarily the key. However, thickness and composition of the cable seems to be the next 'relevant' question. When one goes into a large retailer there are several versions of the HDMI cable displayed at widely varying prices. Any comments [from a 'plain old and somewhat technically challenged consumer']

[rfowkes]

Hi olliesam.

I've heard lots of claims about the "quality" of HDMI cables from some people who have a lot to gain from selling you the "more expensive spread" but have yet to see any tangible (i.e. results you can actually see and hear) proof that thickness, data speed, etc. have any relevance to performance in today's AV world. I'm still firmly of the opinion that as long as the cable is well constructed (and even most of the $10 ones are if you buy from reputable discount places like monoprice.com) you can't go wrong. I sat in at several sessions at CEDIA 2007 where prominent cable manufacturers were extolling their "speed rated" cables - using somewhat suspicious testing methods since they were designed by themselves to try to push "three figure" cables as being better than low two-figure ones. They can show all the graphs and stats that they want but I haven't seen tangible real world benefits.

My advice is to try the inexpensive cable first. If a reputable dealer will let you purchase an "expensive" HDMI cable WITH AN OPTION TO RETURN IT IF YOU DON'T WANT TO KEEP IT then you can see and hear for yourself whether there is a real difference. That's the "try and buy" approach that I advocated in the article. And I still stand behind everything I wrote at the time (about 6 months ago.) The only concern (other than loose connections) with HDMI cabling is length. Once you get beyond about 15-20 feet (your footage may differ) there is a possibility that the attenuation of the digital signal might introduce some threshhold issues (being able to tell 0's from 1's). That's where a cable with a repeater (signal booster) at one end can play a legitimate role. I currently use a 62 ft HDMI cable with a repeater at one end to go from my electronics to my ceiling mounted front projector and it works like a charm.

Finally, while the amount of data being fed through these cables is getting larger a lot quicker than many people thought there is so much headroom in a "regular" HDMI cable already that to me it makes no sense at all to worry about not being able to carry the information today and for the foreseeable future. Yes, the day might actually come where there is so much stuff travelling through the cable that it might become an issue but the manufacturers conveniently leave out the fact that tofday's cables aren't anywhere near capacity and can handle much, much more. But by that time not only will your $10 cables have given you great service but the price of "speedier" cables will probably have dropped to the low two-digit range themselves.

This is digital, not analog - so don't buy into all the snake oil talk. <g>

[Richard]

Just wanted to add to this wonderful article the technical problem with switchers that are not powered.

HDMI terms are SOURCE and SINK. SOURCE, is well, the source component. SINK is the destination such as the input to a TV, A/V receiver or switch.

The HDMI spec uses a 5 volt 20ma SWITCHING signal from the SOURCE that is fed to the SINK and directly connected to another pin on the SINK that goes right back to the SOURCE. It is nothing more than a switch. When the SOURCE sees the 5V returned from the SINK it knows it is actually connected to something and should therefore be talking to a SINK - sending data. When SINK products use that as a power source it can get pulled down to less than 5V and if below the thresh hold the SOURCE no longer sees the 5V returned. Your HDMI turns off because as far as it is concerned it is not connected to anything.

As you point out, manufacturers checking the specs before they manufacture has been the ongoing problem. 5 volts with a measly 20ma of source current is not a power supply source... it can barely light a single LED...

[Roger Halstead]

Agreed and I did take your article the way you meant. I believe it does a good job of explaining to the non technically oriented that they really don't have a problem with their equipment. I just wanted to clarify and add the reason as to why we have HDMI. (or have been stuck with it) BTW I'm also using the $10 specials for my cables<:-))
However I do view the wait while the handshaking is going on as a flaw. A flaw that is inherent in the design of HDMI that depends on both the speed of the chips doing the handshaking/decoding and the complexity of the algorithm required by the DRM. It would cost more to implement but there is little reason for more than a barely perceptible delay OTOH I believe there is also a lot of buffering of the actual video and audio going on inside the equipment which could be a considerable part of that delay.

[MarkyMark]

Hey Robert! Well done. Excellent piece of writing.

Here are a couple of additional comments for those who are starting out...

When I first dove in to high-def I bought my Panasonic 1080p Plasma panel first at Best Buy. They took me over to the HDMI cable rack and the cheap store brand was $80 and it went up from there to about $130 as I recall. A voice in the back of my head said something wasn't right about that, so I declined and went home and re-researched the matter. I mean, a one is a one and a zero is a zero! If only your article was available to me then it would have saved me a lot of time! (I hope this forum is indexed by Google.)

I finally bought some premium $20 HDMI cables from Amazon (under Amazon Prime thank you very much! ) and they are mysteriously molded the same way Monster cables are, but without the Monster logo. he he.

--- The HDMI Connection Diagram In My Head Started Out Wrong

But I also learned that I had the wrong model in my head as to how things were going to be hooked together with HDMI. I was bummed that the TV only had two HDMI inputs and I already had 5 HDMI-ready devices!

I thought that the devices would all go to the TV first, and then the TV would pass through the audio on to the surround sound receiver. WRONG. Not with Panasonic panels anyway. All my devices had to instead go through the surround sound receiver first, so it could "peel off" the digital audio, and then pass the video on to the TV.

Of course, the Onkyo SR605 receiver also only had two HDMI inputs. I decided on the excellent OPPO HDMI switches that automatically switch to whatever device is turned on (and prioritized in the case that your TiVo HD or cable box is always outputting a signal.)

I've never had a lick of trouble, ever!

Mark Hernandez
San Diego, CA

[rfowkes]

Richard, Roger and Mark,

Thanks for the kind words and the additional information that you have all provided. Obviously I agree with the sentiments expressed within and I feel that every little bit of additional data provided to the consumer(no pun intended) is another step forward in the process of HDMI 101.

Well said!

[MarkyMark]

Of course, we all discover that one of the things that makes high-def so confusing is that in some ways it's controlled chaos and a free-for-all with the standards and overlapping and duplicated equipment capabilities. For example, there can be Dolby TrueHD decoding in the player, and in the surround receiver. There can be upconverting and HDMI switching capability in multiple places, as well.

I just realized that by not having an HDMI connection arrangement where each of your devices goes through your TV first, then on to the surround sound receiver second, you miss out on the TV's ability to remember different picture settings for each device. I now find myself having to manually change things depending on whether I am watching Blu-ray, AppleTV, TiVo HD, or the upconverting DVD player. Yeah, they all need a little tweaking. They all have different needs.

The HDMI "connection model" is flawed in that regard.

Though my panel can remember one picture setting for each HDMI input, only one input is being used because everything is being switched elsewhere and moved through the surround receiver first. But then, the TV only has two HDMI inputs anyway, so, it's a mess. If the TV could remember multiple custom settings, that might be a help, but it would still take a call to tech support (that's me) for the family to get it right.

<sigh> Oh well! That's progress! One step forward, one step back.

Mark Hernandez
San Diego, CA