Why did they choose to go with copper wires for HDMI?

[NeoPTLD]

I was watching Innovation episode on fiber optics on PBS and it said something like one fiber optic cable can transmit same amount of data as hundreds of telecom wires.

Most consumer AV equipment have an SPDIF optical output. Why are they still using copper wires for high definition video transfer instead of optical fiber cable when it can supposedly carry way more information than copper?

 

[Cogman]

My guess is cost. Copper is still quite a bit easier to implement in a circuit then optics are. And while it is true that Fiber Optics can transfer more data, we still haven't quite reached the limits of our beloved copper.

 

[Modelworks]

HDMI uses 3 different data streams.
To do that with optical you would need to encode each stream into a different wavelength of light. Then decode that on the other end.

The circuitry to do that is not cheap, copper does the job at a reasonable cost.

 

[firewolfsm]

HDMI gets the job done, HD screens don't need that bandwidth yet so they just go with what's cheaper.

 

[NeoPTLD]

Well, if they can use it for SPDIF audio and if one fiber optic has enough bandwidth as thousands of copper, doesn't the same fiber optic cable used for SPDIF have more than enough bandwidth to carry HDMI signal?

 

[Modelworks]

Originally posted by: NeoPTLD
Well, if they can use it for SPDIF audio and if one fiber optic has enough bandwidth as thousands of copper, doesn't the same fiber optic cable used for SPDIF have more than enough bandwidth to carry HDMI signal?

Its not that fiber can't be used for hdmi.
Its that its too expensive.

The components to encode and decode that signal in real time over fiber are in the $200 + range.

Do you really want to pay $200 more for something just so it can use a fiber optic cable ?

 

[silverpig]

Originally posted by: Modelworks

Originally posted by: NeoPTLD
Well, if they can use it for SPDIF audio and if one fiber optic has enough bandwidth as thousands of copper, doesn't the same fiber optic cable used for SPDIF have more than enough bandwidth to carry HDMI signal?

Its not that fiber can't be used for hdmi.
Its that its too expensive.

The components to encode and decode that signal in real time over fiber are in the $200 + range.

Do you really want to pay $200 more for something just so it can use a fiber optic cable ?

TOSLINK? There are already fiber optics for audio.

The answer is it isn't needed. If a semi-truck can carry more than a hatchback, why doesn't everyone have one to drive the kids to school with? It probably costs a bit more, and that extra cost isn't needed.

 

[funkymatt]

Originally posted by: silverpig

Originally posted by: Modelworks

Originally posted by: NeoPTLD
Well, if they can use it for SPDIF audio and if one fiber optic has enough bandwidth as thousands of copper, doesn't the same fiber optic cable used for SPDIF have more than enough bandwidth to carry HDMI signal?

Its not that fiber can't be used for hdmi.
Its that its too expensive.

The components to encode and decode that signal in real time over fiber are in the $200 + range.

Do you really want to pay $200 more for something just so it can use a fiber optic cable ?

TOSLINK? There are already fiber optics for audio.

The answer is it isn't needed. If a semi-truck can carry more than a hatchback, why doesn't everyone have one to drive the kids to school with? It probably costs a bit more, and that extra cost isn't needed.

but everyone seems so intent on getting a giant SUV. :laugh:

 

[Modelworks]

Originally posted by: silverpig


TOSLINK? There are already fiber optics for audio.

Toslink would not work.
Digital audio is a single bit stream.
To use it for hdtv you would have to use 3 seperate cables for the video plus a 4th cable for the audio.

Fiber for audio is designed for one data stream only.

When you see one fiber carrying lots of different data streams , like those used in internet backbones, those are done by using multiple wavelengths of light on the same cable. Its very expensive to encode and decode.
http://en.wikipedia.org/wiki/W...-division_multiplexing

 

[spidey07]

It's all a question of bandwidth AND cost. TosLink maxes out at 10 megabits per second. That's nothing and surely not enough for HD video. While toslink can be called fiber optics, it's not "real" fiber optics used in communications. Toslink has like a 3 millimeter core, or the actual piece of fiber. This means light bounces all around in there and hence the low bandwidth. Plus LEDs are used which physically can't switch on and off fast enough for really high speeds needed.

Compare this to "real" fiber optics. The core for multimode fiber is 50 or 62.5 microns thick. That's pretty small. This is normally sufficient for speeds up to 10 gigabits per second for short disances, but even then the optics required are VERY expensive, thousands of dollars on each end. Not really suitable for home use. Sure for lower speeds the optics would be cheaper, but still not what a manufacturer wants to put into home gear.

Then you have single mode fiber. Core size of 8 microns. This allows light to operate in a single mode with little refraction or reflection in the cable. This means much "cleaner" light and less noise/loss. The possibilities are virtually endless with this kind of fiber, it all depends on how much you want to spend to light it. 200,000 dollars just for the optics alone are not unheard of. Lasers are used here because of the very precise wave they generate.

So cost and bandwidth are the real reasons. It just isn't practical to use fiber for high bandwidth applications in the home. Twisted pair copper cabling can do the job cheaper. Coming real soon you'll have 10 Gigabit/sec ethernet on twisted pair copper cabling.

 

[PlatinumGold]

Originally posted by: Modelworks
HDMI uses 3 different data streams.
To do that with optical you would need to encode each stream into a different wavelength of light. Then decode that on the other end.

The circuitry to do that is not cheap, copper does the job at a reasonable cost.

why not just use 3 strands of fiber?

 

[bobsmith1492]

Originally posted by: spidey07
It's all a question of bandwidth AND cost. TosLink maxes out at 10 megabits per second. That's nothing and surely not enough for HD video. While toslink can be called fiber optics, it's not "real" fiber optics used in communications. Toslink has like a 3 millimeter core, or the actual piece of fiber. This means light bounces all around in there and hence the low bandwidth. Plus LEDs are used which physically can't switch on and off fast enough for really high speeds needed.

Compare this to "real" fiber optics. The core for multimode fiber is 50 or 62.5 microns thick. That's pretty small. This is normally sufficient for speeds up to 10 gigabits per second for short disances, but even then the optics required are VERY expensive, thousands of dollars on each end. Not really suitable for home use. Sure for lower speeds the optics would be cheaper, but still not what a manufacturer wants to put into home gear.

Then you have single mode fiber. Core size of 8 microns. This allows light to operate in a single mode with little refraction or reflection in the cable. This means much "cleaner" light and less noise/loss. The possibilities are virtually endless with this kind of fiber, it all depends on how much you want to spend to light it. 200,000 dollars just for the optics alone are not unheard of. Lasers are used here because of the very precise wave they generate.

So cost and bandwidth are the real reasons. It just isn't practical to use fiber for high bandwidth applications in the home. Twisted pair copper cabling can do the job cheaper. Coming real soon you'll have 10 Gigabit/sec ethernet on twisted pair copper cabling.

Don't they already have that, only using all four pairs in a network cable? Do you mean quadruple that speed, i.e. 40Gb/s using all four pairs?

 

[spidey07]

There are proprietary interconnects using twisted pair to achieve greater than 1 Gbs. The 10 Gbs ethernet on twisted pair is coming, possibly this year. Both 1G and 10G use all four pairs.

 

[spidey07]

Originally posted by: PlatinumGold

Originally posted by: Modelworks
HDMI uses 3 different data streams.
To do that with optical you would need to encode each stream into a different wavelength of light. Then decode that on the other end.

The circuitry to do that is not cheap, copper does the job at a reasonable cost.

why not just use 3 strands of fiber?

Why not just use copper in a single cable? Saves space and cost. Oh, and the "real" fiber cable I was talking about is cheap, not much more than copper. It's the optics to transmit and receive at high speed that are so expensive. Plus there's the safety aspect. You don't want home users burning their retina with lasers. 😉

 

[bobsmith1492]

I know they already have 10Gb/s over copper - a friend of mine showed me an (insanely expensive) cable analyzer that tested them assuring they could handle that speed.

 

[spidey07]

Originally posted by: bobsmith1492
I know they already have 10Gb/s over copper - a friend of mine showed me an (insanely expensive) cable analyzer that tested them assuring they could handle that speed.

He may have scanned the cable to that speed, doesn't mean there is a standard out there to use it for any real distance.

Most of the current cable scanners will go that high, and they're not that expensive. 5-6K.

 

[bobsmith1492]

Originally posted by: spidey07

Originally posted by: bobsmith1492
I know they already have 10Gb/s over copper - a friend of mine showed me an (insanely expensive) cable analyzer that tested them assuring they could handle that speed.

He may have scanned the cable to that speed, doesn't mean there is a standard out there to use it for any real distance.

Most of the current cable scanners will go that high, and they're not that expensive. 5-6K.

This thing was slick, though; it measured, graphed, and recorded a huge list of properties, did a broad frequency sweep to measure impedance and other things. I think it was something in the 100K dollar range. (!)

 

[TuxDave]

Originally posted by: Modelworks
HDMI uses 3 different data streams.
To do that with optical you would need to encode each stream into a different wavelength of light. Then decode that on the other end.

The circuitry to do that is not cheap, copper does the job at a reasonable cost.

What's stopping them from dividing up the stream in time so that if you need 3 data streams, just splice them together and send the data out 3x as fast.

My 2nd question is, so we say fiber optics can carry more than copper wire, but I guess they're comparing dense wavelength division multiplexing vs using multiple carrier frequencies (within its bandwidth spec) for copper. But assuming the cheapest of the cheap meaning only a single frequency demodulator so each of them are using only one frequency, which one would carry more data and by how much?

 

[Modelworks]

Originally posted by: TuxDave
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What's stopping them from dividing up the stream in time so that if you need 3 data streams, just splice them together and send the data out 3x as fast.

My 2nd question is, so we say fiber optics can carry more than copper wire, but I guess they're comparing dense wavelength division multiplexing vs using multiple carrier frequencies (within its bandwidth spec) for copper. But assuming the cheapest of the cheap meaning only a single frequency demodulator so each of them are using only one frequency, which one would carry more data and by how much?

Cost.
Full HD stream bandwidth is 1.4Gbit/sec .
Thats for one channel , multiplexed.
The way it is now, you have each of the 3 data streams carrying 500Mbit/sec.
To do what you suggest you would need to use high end dsp in the tv, adding significant cost without any real benefit over copper. Also laser diodes add even more cost , as well as danger from people getting eye damage.

If they had really wanted to use fiber to connect HDTV devices, the way to do it would have been to send the raw data stream directly to the tv. Then they could use one fiber to carry everything. The problem is there is no standard for what the raw data stream format is like. Blu-ray may have one way, Satellite and cable another.

It would have added confusion to hdtv. Imagine shopping for a hdtv and having to find one that is HDTV type A signal, type B signal, type c signal. It was best to break down the signal into its components allowing the receiving device to assemble however it needed them.

 

[soccerballtux]

Originally posted by: NeoPTLD
Well, if they can use it for SPDIF audio and if one fiber optic has enough bandwidth as thousands of copper, doesn't the same fiber optic cable used for SPDIF have more than enough bandwidth to carry HDMI signal?

But there's really no need for it.

 

[spidey07]

Originally posted by: soccerballtux

Originally posted by: NeoPTLD
Well, if they can use it for SPDIF audio and if one fiber optic has enough bandwidth as thousands of copper, doesn't the same fiber optic cable used for SPDIF have more than enough bandwidth to carry HDMI signal?

But there's really no need for it.

Not to mention that SPDIF and toslink in general are severely bandwidth limited and can't carry HD video.

It's a question of bandwidth and cost. With a little bit of consumer safety and lasers thrown in.

 

[soccerballtux]

Originally posted by: spidey07

Originally posted by: soccerballtux

Originally posted by: NeoPTLD
Well, if they can use it for SPDIF audio and if one fiber optic has enough bandwidth as thousands of copper, doesn't the same fiber optic cable used for SPDIF have more than enough bandwidth to carry HDMI signal?

But there's really no need for it.

Not to mention that SPDIF and toslink in general are severely bandwidth limited and can't carry HD video.

It's a question of bandwidth and cost. With a little bit of consumer safety and lasers thrown in.

Um, yes, but you could also say "well copper is bad because telephone lines are bandwidth limited". Fibre has more potential for insane bandwidth than copper does, esp over long distances; that's why everybody uses OC192 and not STS192 :/

 

[Fox5]

I'm surprised nobody mentioned the durability aspect.
From my understanding, copper wires are less likely to break under bending and twisting than fiber.

 

[Modelworks]

Originally posted by: Fox5
I'm surprised nobody mentioned the durability aspect.
From my understanding, copper wires are less likely to break under bending and twisting than fiber.

Thats true as well.
I don't think they ever got to that part of the equation though, since they always start with cost.

 

[RaynorWolfcastle]

Fiber is more fragile than copper although for consumer applications you can usually put a jacket on it that's stiff enough to prevent it from happening (remember that the actual fiber itself has a radius that's much smaller than 1 mm).

As Spidey has mentioned, while the fiber itself is cheap the rest of the equipment is definitely not and can easily cost hundreds of dollars even for a setup with relatively modest performance (see FTTH costs, for example). At the moment, fiber is really only worth it when you need either long reach or very high performance, it'll be a while before it can compete with copper for short runs/low perf applications like HDMI.