AVS Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #1 ·
This isnt a specific question, but I'm curious as to why the powers that be decided to make HDMI over copper instead of optical.


To me optical just seems like the way to go. With copper prices being ridiculous and optical being so cheap and (to my knowledge) vastly superior I just can't figure out why they would make that decision.


Maybe each end user device would cost to much each converting the optical signal to electric???
 

·
Registered
Joined
·
556 Posts
Plastic optical fiber is lousy for attenuation and bandwidth. Glass, meanwhile, is prone to damage when handled, as the consumer inevitably will, in a rough way. I don't know too much about the cost of the optical conversion--I do know that when people make boxes to that to an existing HDMI connection, it gets costly quick.


Kurt
Blue Jeans Cable
 

·
Banned
Joined
·
20,735 Posts
It is also, historically, a lot more expensive than copper twisted pair which is pretty darn cheap. And given that HDMI wasn't really designed to go long distances, optical doesn't make a whole lot of sense. Unfortunately, now everyone is trying to do HDMI over fiber optics because you can't go very far with twisted pair copper at these bandwidths...
 

·
Registered
Joined
·
1,755 Posts
It's a guess, but I think the cost of the electronics to transfer the high frequency HDMI signal over copper is (or was) significantly cheaper than the electronics to transfer it over optical. In the consumer world, cost rules. For example, present devices that transfer HDMI over optical are at least $400 whereas an HDMI booster amp for cable can be had for $30 or less.


That's not the case for digital audio which has a much lower frequency and consequently an optical connection doesn't add significant cost to the electronics.
 

·
Registered
Joined
·
302 Posts
Im in the same opinion as the others who posted here, it would need to be glass strands and not plastic to have high bandwidth at longer distances, and that is both expensive and fragile. Both are the biggest concerns when making a consumer product.
 

·
Registered
Joined
·
116 Posts
Fiber is expensive, that's what. Not just the cable, but the transceivers as well. One of the advantages of using multiple copper wires, as is done with HDMI, is that you can transfer more data at a lower rate because you do it in parallel. In the case of HDMI, red, green and blue are all transferred on different wires.


Ok well unless you are going to have multiple fibers, which is a whole different mess, you are doing it all on the same cable. That means you either need a higher frequency transceiver to handle the increased data, or you need to have multiple transceivers on different frequencies of light and combined them as is done with CWDM signals.


Big costs here, not something you want for consumer gear. As an example, suppose you have a 10gb capable network switch, and you wish to add a short range fiber transceiver for it. Price? About $800. That is just for one end, and that is already on a switch that supports it. More or less the $800 is just for the processor and lasers necessary to move the data. Ouch. You want that kind of cost in a consumer device?


There ARE HDMI to fiber converters/extenders. Gefen has one for $1500 as an example. So in the event it is needed it can be done, but it is way too expensive to do for most devices. In normal homes, copper covers all the distances needed very nicely and at a price that isn't too bad.


Do remember that in the networking world, we've had fiber for decades. Any Ethernet technology you can get over copper, you can also get over fiber (and there are some that are fiber only). However, we still use copper to the desktop in almost every case. The reason is cost, pure and simple. You only go fiber when you distances or bandwidth exceed what copper can do.
 

·
Registered
Joined
·
18,923 Posts
I am no expert, but I think differential signaling with three data lines allows for faster speeds than maybe a single string of plastic optical could provide.
 

·
Registered
Joined
·
92 Posts
Michael,


Actually a single fiber can provide many, many times the bandwidth of an HDMI cable. Using a single wavelength we currently can go up to 40Gbps - soon 100Gbps. Using multiple wavelengths we can get even more bandwidth (look up DWDM if you're interested). So right now we can do 64 wavelengths at 40Gbps to acheive over 2.5Tbps over a single fiber. Of course this is extremely expensive, although not due to the fiber itself but due to the electrical and optical components.


Optical fiber is actually relatively cheap. Much cheaper than HDMI cable. It is the electrical-to-optical and optical-to-electrical portion that is expensive, but the prices are always dropping. Maybe in 5-10 years it may be cheaper to manufacter a 20m+ optical HDMI cable than a copper one.


The real question we should be asking is why didn't the consumer industry adopt SMPTE's method for transporting digital video over 75ohm coax. Of course the answer is that it is not copy protected. Could you imagine if we could use 75ohm coax to run and distribute 1080p signals around your house? It would be an A/V installer's vision of heaven.
 
1 - 8 of 8 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top