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Comment by micks56 | Hacker News Reader

I think your understanding of cables is off.

All signals are analog. Every single one. (Actually, I take that back. With the exception of quantum computers, to date, all signals are analog).

A "digital" cable doesn't just work or not work. It is possible to receive spurious bit errors for many reasons. For example, you turn up the volume to your awesome surround sound speakers, which causes more current to flow through your speaker wires that happen to be running parallel to your horrible HDMI cable. The increased current causes interference in your low-power HDMI cable, causing bit errors in the transmission.

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>> "It is possible to receive spurious bit errors for many reasons."

Surely that's why there's error correction layered on top?

Instead of arguing about what might happen, why not find an HDMI device that'll show you how many unrecoverable bit errors it has detected in the stream... Can't be that hard to do.

If my hard disk can send data over a tiny crappy unshielded cheap USB cable without a single bit error, I'd be willing to bet money that an HDMI cable isn't that much different.

HDMI doesn't do error correction for video.

ugh, I hated signals theory at uni... but let me dust off that knowledge...

> All signals are analog.

I see your reasoning in saying this ("on the wire" etc.); your incorrect though. Not all signals are considered analog (which is important to the point being made)

Analog signals are generally susceptible to noise because they are usually non-recoverable; error checking is hard because it is a non-discrete continuous signal.

>It is possible to receive spurious bit errors for many reasons.

Yes, which is why error checking exists in all these systems. In the context of the wire alone, yes, it is not a case of "it just works". But in the case of the communications subsystem (i.e. the transmitter, medium, receiver) it really does either work or not work :)

Ultimately thought the phrase "it's digital; either it works or it doesnt" is making no comment about the actual signal. It's really saying: an expensive cable is not, due to the digital sub-system, likely to make any difference to error rates (or more succinctly: the performance of the error correction is better than the noise affect of the transport medium)

Isn't HDMI supposed to do error correction on both sides, though? I could be totally making that up, I thought I remember hearing that a while back.

There is this weird thing called error detection/correction.

which HDMI doesn't do.

Hm, no idea, but I find that very hard to believe. I suspect digital transmission of information is almost impossible without error correction. IANAEE, though (I am not an electronics engineer).

HDMI does have error correction. Every 8 bits of video data are sent as 10 bits on the wire.

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