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What is the point of High-End ($$) A / V wires, when it all comes in on Coaxial?

It dawns on me that HD cable service and HD satellite service come to my components by coaxial cable. Now, most everything I have ever seen about quality levels from different wire types shows coax at the bottom of every list. So, what is the difference between the wire that brings in the signal, and the wire that connects to my components? Is it because the signal processors that use the coax connection are anlaog, only? If coax can bring the HD digital signal to my house, why can’t a TV use the HD signal on coax?

An easier question to ask than to answer properly!

The main thing to understand is that what comes over the cable and into the cable box (or satellite box) is a different type of signal than what comes out of the box and the different signal types can be degraded in different ways.

A cable TV cable coming to your house (or the cable coming from the satellite dish) contains information for many different channel signals spread across a wide frequency spectrum. For digital signals, which you seem to be most interested in here, the picture as well as the sound for *every channel* you can get is there on the cable, encoded digitally at one frequency or another. The broadband cable is designed to carry all these signals at the same time to the decoder box, and does a fine job of it.

The job of the box is to select and decode *just the channel you want to watch* and send that signal to your TV and/or sound system. However, your eyes and ears cannot sense digital data, so at some point the signals must be converted back to analog. This is where a lot of the confusion comes in. Once the signals are analog they are subject to degradation.

The rankings of quality for different types of cables (with coaxial on the bottom) have to do with the type of signals they carry. This is mostly an issue when you are sending an analog signal from the box to the TV.

The reason composite (which is transmitted by an RCA cable that you are thinking of as “coaxial”) is on the bottom of this list is not so much because coaxial is bad cable (it’s not), but because this particular coaxial carries an analog signal that is already a kludge – a modulated combination of a black-level (lumina) and color information (chroma). A device called a comb filter in your TV must seperate out these two components, potentially causing signal degradation.

Next on the quality list is S-video, which uses different wires to carry the chroma and lumina information, which is better but still requires the TV to decode color information from the degradable analog chroma signal. Even better is component cables which sends the analog signal for each color independently.

Each of these analog cable options is actually “coaxial” in construction! So it’s not the cable type, it’s the *signal* type that leads to differences in ultimate quality. This is why you want to use decent cables to transmit the signals without degradation, but recognize that high-priced “exotic” cables are still subject to the limitations of the signal type.

Now, in the HDTV world, things are a bit different (pun intended). Your HD cable box will still output analog signals which are subject to some of the same types of degradation as standard analog signals. A bigger problem is that the TV now has to digitize that signal (that started digital but is now analog) back into a digital format and re-map it to pixels, resulting in some degradation.

So the best objective is to get the signal to the TV in digital format and let the TV do the decoding more or less directly to the pixels. In this case the box is just picking out the right channel and converting it to bits that are sent to the TV and/or sound system. Often the digital bit stream for audio and video signals are seperated. And, in fact, again all the different options are essentially coaxial cables in different forms.

Here, you are absolutely correct in thinking that any cable that can successfully get the bits from one place to another will work equally well. In the digital realm there is even less reason to use exotic or expensive cables. But because there are multiple bitstreams involved, there generally needs to be more than one wire used and thus multi-connection formats such as SPDIF and HDMI (really just multiple coaxial wires bundled together) are used. Since these cables are mechanically more complex than a single-signal RCA cable they can be a little more expensive, but there is still no need for a “fancy” expensive version where a simple one will do.

Also, it *is* technically possible to just run the same cable that comes into the house directly to the TV, provided that the TV has an integrated digital cable tuner (or “cable card” capability). All the connections and converstions I talked about above are still present, they are just being done internally to the set.

Whew! Hope this helped.