Why do we need HDMI cables

nsxxtreme

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Would love to here from an expert why we need a HDMI cable?

The industry insists on pushing snake oil cables. We are dealing with digital signals here. Its either there or its not. We already have a digital Toslink cable for audio. Which is what I dont understand Fiber essentially has unlimited bandwidth. Cable "wire" had impedence and capacitance to overcome. If we could push both over a single fiber why introduce an additional cable that is inferior? Must be so we can justify a gold plated super low impedence magical HDMI cable.

I can somewhat understand the switch from DVI to HDMI just for the smaller connector. But why not use a cable that does not have the anolog drawbacks?
 

ChristopherDAC

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DVI and HDMI are parallel signal interfaces. In other words, the digital R, G, and B signals are transported simultaneously along separate wires.

Since computer video is generated as synchronous RGB signals, this means that DVI is very compatible with computer video systems, which is its design application. HDMI is essentially built as an extension to DVI. While consumer electronics could just as easily use the SDI connection system (Serial Digital Interface, as its name implies, a one-wire solution) which is standard for professional work, the consumer electronics companies prefer to have something which is (a) capable of more flexibility with respect to timings, and (b) not compatible with professional equipment.
 

nsxxtreme

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Fiber can go far beyond 125Mbps. I dont know where you got that info. I used to build 10km 10GB/s fiber optic modules.
 

nsxxtreme

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I dont know if I buy those those arguments.

My tv uses a DVI connection. This is a large connector and I could see the manufacturers switching for a smaller connector and additional features of sound and copy protection built into the HDMI spec.

But it doesn't answer why they didn't just use fiber. Serial transfers are less dependent on timing then a high speed parallel connection. Even though the signals are transmitted in parallel they still have to be in sync.

The advantage of parallel is you could run at a slower speed to transmit the same amount of data. Thus making the TX and RX recievers cheaper.

It sounds as though they are trying to go to a single cable to handle audio and video which is great. I just wish they would improve on a technology they already have instead of making us go out and buy new cables. It would be interesting to find out the bandwidth limit and length restrictions built into this cable to see if they have any headroom for future expansion.
 

ChristopherDAC

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Well, you have to remember, you were dealing with carrier-wave type applications. This is a baseband application. It's like the difference between composite video and television-antenna signals going over the same RG59 cable. What "existing cable" would you want to use, anyway? SDI could, for short lengths, use a single standard 75-ohm cable, the same as is used for composite video (assuming it's good quality), and it does have embedded audio. On the other hand, its bit-depth, colorspace, and scanrate are specified in ways which might be too restrictive for today's consumer applications. If they went with a fibre-optic link, you can be sure they wouldn't be using TosLink cables ; even a TosLink could carry the datarate, the potential for confusion would be enormous. Really, why do you resent having to buy one new cable? I mean, there is no "technology they already have" in terms of consumer digital video links. DVI is it, and HDMI is just an extension of DVI — in that sense, it is building off existing technology. You can use a DVI cable for HDMI, if you just put a DVI-HDMI adapter at each end.
 

nsxxtreme

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Again where are you guys getting this misinformation?

I have built 10 gigabyte/s not gigabit fiber optic modules.

Try doing a web search for 10GB/s optical modules. This obviously isn't over a toslink connection. But that is problem with the connector not the fiber.

Would post a link but I cant yet

Try going to linktionary.com they have a decent read.
 

John Garcia

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We are not talking about fiber optic as a whole, and NETWORK fiber optic is NOT the same thing as HOME THEATER fiber optic, aka EIJA - it is limited to 125mbps because of the equipment AND the specication; and is also limited to 10 meters and a realistically usable length of 5 meters without augmenting due to signal loss with the light levels put out by home gear. I worked at a fiber optic company that MADE the network switches for the largest networking companies in the world, I have a little experience with them...yes fiber is capable of immense transmission, but I don't see the industry moving to network type fiber gear anytime soon. HDMI was chosen because it is simple and inexpensive to implement across all forms of gear, similar to why USB is also so common.

ChristopherDAC hit the nail right on the head too - you DON'T want your video and audio all transmitted via ONE cable....this creates smear in BOTH signals.
 

nsxxtreme

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We are not talking about an analog signal here. Any newer system is digital, your only limitation is the ability to transmit the data.

Your speed limitation is in the toslink connector. This could easily be changed for a different connector. But then we are switching cables again.

The cheaper fiber systems use LED's instead of lasers. LED's are usually used for consumer electronics and have limited range. Laser are usually used for higher end optical systems. The last time I was working on fibers was 3 years ago. A 10GB/s optical TX and RX would cost you $250. Far cheaper by now.

Maybe there is just no need for the speed of fiber right now. If not what was the point of introducing it to begin with. I just get tired of all the new connections. Fiber was more then enough to satisfy any future growth if done properly. Now they want us to buy into HDMI.
 

John Garcia

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Um, smear occurs with optical too....it was quite common early on, but with the progression of LEDs recently, it has vastly improved. More data in there and you begin to have a problem all over again though.

When optical first started to become common, I thought it would quickly take over as the defacto connection type, including in car audio, but that never happened either.
 

nsxxtreme

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A digital signal is either a 1 or a 0. There is no mixing of signals. It's either there or its not. So I don't know what your refering to when you say "smear"

You can stuff as much as you want down the pipe as long as your TX and RX are capable of handling the bandwidth. The Fiber is only used as a means of propogating the light from the TX to RX. There is no difference between video and audio data from the transmitter and receiver view. It dosen't care what the data is, its just a means of transportation fom point A to point B. To Further this point your HD DVD player uses the same optical pickup for audio and video.

If fiber was the standard Monster cable and all the other snake oil wire companies would go out of buisness LOL.
 

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