Analog transmission cables

[El Greco]

I was looking at this Scart->S-video cable (http://www.hama.de/portal/articleId*56341/action*2563) and was reading its "highlights":

- High-density shieding, that is to say, double-shielded for the purpose of inteference-free signal transmission
- Equipped with a sprayed plug for the purpose of bend protection and strain relief
- 24 K gold-plated, that is to say, hard gold plated contact surface for the purpose of loss-free transmission
- Equipped with OFC cables, made out of oxidation-free direction material for the purpose of minimum transition loss
- Top-grade PE insulator, special dielectrics for an ideal capacity values
- Outside diameter: 4/5/4 mm

Do the above characteristics offer a distinct advantage over a more ordinary adapter cable, or are they in the realm of the audio/video woo ? Can one expect an improvement in picture quality with such a cable with a good DVD source and a good TV or projector ? What if the source is ordinary PAL TV signal ?

[TobiasTheViking]

i doubt more than one layer of shielding will make any difference.

Sprayed plug, no idea what it is.

Gold will make the quality better, but, again, i doubt enough that it makes a difference, anyways 24 K is way overkill(and i don't see why they would waste that amoung of gold on a plug)

Oxidation free direction material.. total crap, most cables are oxidation free, or oxidates so slowly it doesn't matter(imo). As for the direction part, i have no idea what that is about.

PE insulator and special dielectrics, don't know what it is, sounds woo'ish.

I'm sure fowlsound or someone else will be able to say something better than me.

Any normal, bland, cable will do. There is no need to invest in expensive cables.

[TobiasTheViking]

Look, get the plugs, use some normal power wire between the plugs, add some tin foil around it, it should be fine. With that in mind, do you think that the product above is worth the price?

[The_Fire]

Gold is only a viable solution in noisereduction if the entire conducting circuit (here: the cable innards) is made from the stuff.
In this instance you can almost bet that the cable between the two plugs is ordinary copper. No diffrence.

Double shielding: Sounds like audiophile-woo to me. Everything I've worked with so far have worked with singlelayer. And that includes some full-professional stuff (which makes my own question from a while back all the more embarasing).

Sprayed-plugs: Unless the plug-cuff is extending more than the usual, the only difference this makes is that it wont fall apart in your hands. The "Bendprotection" is dependant on the cuff-length and also HOW the cuff is attached. Some of the pro-plugs (mainly XLR) have a stress dependant cuff-lock: The more you stress it, the more the cuff locks on the wire to prevent it from getting yanked out of the plug. However, unless you plan on hanging your equipment from the ceiling in the wire, this doesn't make much of a difference.

Oxidation-free: THe commie already covered that one.

PE-Insulation: Ehh....If the advertiser by that means a noisereduction circuit, then it CAN make a slight difference in how much noise makes it through allthough THAT have NOTHING to do with capacity and everything to do with how much electromagnetic interferrance makes it though the shield.
Noteworthy on noise: "Noise" originates as a result of the magnetic field->electric charge -> magnetic field thing. Can't remember the names of the people whom actually formulated the two theories. What happens is that a nearby electric utility generates a small magnetic field which again generates a small DC-charge in the wire. This charge is normally caught by the shield and deposited in the ground connection (which is why it's a good idea to have one of those as a standard when dealing with AV-stuff). The signal you want is an AC signal. What is probably important for you to note is: The longer the cable, the longer the possibility of catching noise. Don't buy anything longer than you absolutely have to.

Most of the video noise removing circuits I've seen for wires so far seems to consist of a magnet, bugger me why, but it works. They can also be aquired loose.

In other words: Buy a cheaper cable. The noise reduction circuits can, if you need them, be bought seperate. And the rest seems like woo to me.

[ZirconBlue]

I work in the wire and cable industry, so perhaps I can be of some assistance.


- High-density shieding, that is to say, double-shielded for the purpose of inteference-free signal transmission


Double-shielding can be beneficial in certain applications. A braided shield usually can't give you more than 95-97% coverage. Adding a second braid (or foil tape) increases the shielding effectiveness. Whether this will produce any noticeable benefit for your application is doubtful.

- Equipped with a sprayed plug for the purpose of bend protection and strain relief

I have no idea what a "sprayed" plug is, but you do want to have some sort of strain relief at the ends to prevend conducts from breaking off at the connector (where the cable is usually subject to being bent). Should be standard on cables of this type.

- 24 K gold-plated, that is to say, hard gold plated contact surface for the purpose of loss-free transmission

To the best of my knowledge the main reason for using gold contacts is to make a better electrical connection. It's not woo in theory, but may, once again, be unnoticeable in application.


- Equipped with OFC cables, made out of oxidation-free direction material for the purpose of minimum transition loss


Um, what? You typically don't have issues of oxidation of the conductive materials unless they are exposed to the elements (or in the case of some Teflon materials in direct contact with bare copper); this sounds like a non-feature to me.

- Top-grade PE insulator, special dielectrics for an ideal capacity values


I assumed this is a reference to polyethylene- a common dielectric material in electronics applications. Polyethylene has good electrical properties, but isn't exotic. Should "capacity" have been "capacitance", by any chance?

- Outside diameter: 4/5/4 mm

Unlikely to matter unless you have a tight hole to fit it through.


Do the above characteristics offer a distinct advantage over a more ordinary adapter cable, or are they in the realm of the audio/video woo ? Can one expect an improvement in picture quality with such a cable with a good DVD source and a good TV or projector ? What if the source is ordinary PAL TV signal ?

I suppose that the clearer your picture to start with, the more noticeable noice issues will be. But, I don't think this cable is offering any special features worth paying for. That is, most any adapter cable you can find should be similar in construction and performance. But they all have to have a bulleted list of "features", I guess. I would make my decision on price, if I were you.

[bjb]

Gold is a worse conductor than copper, only 75% as conductive, so a gold-plated connector actually has more resistance. Even so, gold plating is common because it prevents the connectors from corroding and the plugs will make good contact for many years.

Electronic circuits are designed to withstand a certain amount of DC resistance in the signal path. The contact resistance of a good connector will be in the milliohm range, or thousandth of an ohm, but a video input circuit should be able to stand an extra 1000 ohms or so before the signal begins to degrade. This is 1,000,000 times as much resistance than you get from a piece of wire, so paying more for a signal cable that has less resistance makes no sense at all. The same goes for cable capacitance. The video source should be designed to tolerate the capacitance of an ordinary cable without signal degradation.

That video cable looks nice, though. Those plugs look like Neutriks, which are very well-designed connectors. I've used other types of connectors to make cables and the Neutriks have a better strain relief design than some other brands. This is useful for musical instrument cables because the cables are plugged in and unplugged many times. For a TV, though, I just leave the cables in place so the strain relief doesn't do much good.

Personally, I use the rather lousy cables that came with my home theater system and everything looks and sounds good to me.

[jj]

#include <sarcastic.h>
Welcome to the wonderful world of wire.

Gold-plated plugs do make the best connections over time, when connected to gold-plated connectors. Mixing a tinned connector with a gold-plated connector is a no-no. I don't know where to find it since Bell Labs, but look up "solid solution" of tin and gold. Over a long term, it gets bad.

Double-shielding has some place in single-ended (i.e. not balanced) connections, sometimes, in bad conditions.

The question is more "is it assembled right and did they use good connectors".

In audio (didn't realize it reached video) there is enough fertilizer and wire-woo to last a lifetime.

Inexpensive, well constructed, proper cable (and for video proper impedence) is all that really matters.

Btw, strain relief is good, but what a sprayed cable is I have noidea.

[El Greco]

Thanks people. I ended up buying a few gold-plated cables, not because of the gold, but because several comments here made me think that the general construction quality might be better (and because the simpler cables were only 2-3 euros cheaper). I have two TV-tuners, one from a VCR and the other from a PC TV-card and I've been trying various combinations of cables trying to get the best TV picture on the projector. The thing is rather complicated because the PC card is also a DVB-T receiver and so I have to get the digital channels from there. But for the analog channels I get a better picture from the VCR. So I have various sources and in order to be able to change between them without plugging/unplugging I drive everything through the S-video inputs of the receiver which has selectable output. But this also inevitably introduces some distortion from the receiver itself. I still get the best TV picture with a single composite connection between the VCR and the projector, but I figure there must be some way to get better picture with S-video connections... but I can only use the s-video-out of the PC-card because the VCR doesn't have an S-video-out, and when I use Scart to S-video adapters I only get black & white picture. Meanwhile, I could use the DVI to HDMI cable from the PC to the projector but unfortunately when watching football from the TV-card receiver the picture is not smooth (same problem that older LCDs had, and I don't know whether to blame the TV-card or the appilcation that came with it).

I'd go on, but you have probably stopped reading by now :D

[jimlintott]

In audio (didn't realize it reached video) there is enough fertilizer and wire-woo to last a lifetime.
Oh, it's definately reached video. I see reports of some cheap HDMI and DVI cables not working well at all. I have seen uni-directional component cables that actually were. I don't know what they had going on but the picture looked terrible with the cables on backwards.

Pretty much the same rule of thumb in video as audio; both the cheapest and most expensive are a waste of money.

With a lot of flat panels and projectors using seperate power cords (as opposed to built in) there will be power cable woo showing up soon in video (if there isn't already). Luckily in video there is no real equivalent to the speaker wire.

I predict that someone will start selling special lag screws for mounting flat panels. After all you wouldn't want your $6K plasma mounted with plain old steel lag screws, would you?

[bjb]

Sounds like a nightmare. Now I know why people waste money on expensive video cables. They're trying to make up for even more expensive hardware problems!

[bjb]

There are directional cables that have the outer shield connected at one end only. There are two inner conductors that carry the signal, so the shield is isolates from the signal conductors and helps prevent ground loops. Reversing a cable like this can put more noise into the signal path.

For maximum shielding, the end of the cable connected to the shield should be connected to the input side of the signal path. The source end does not have the shield connected. However, Monster cable sells directional cables and they ground the 'source' end of the shield, not the 'input' end. I'm pretty sure this is not the best way to do it but it seems to work anyway. Monster does give an adequate description on how to use their directional cables:

Why do the cables have directional arrows?
This is done for shielding purposes only, a design where we do not solder the shield on the signal’s destination. This ensures that any noise picked up by the shield will not be transmitted into your signal path.

Will I notice a difference if I hook up my cables in the wrong direction?
You probably will not, but if you think that you are experiencing noise problems, check that they are. Cables are directional for shielding purposes only. Should you not see these arrows, remember that the signal flow should go in the same direction of the print on the cable jacket, reading left to right away from the source (source to destination)

What is the "source" in terms of connecting my cables?
The source would be the origin of the signal or sound. This would be a CD player, phono player, VCR or whatever is generating the music or video and the arrows should point away from these "sources".

[jimlintott]

Sounds like a nightmare. Now I know why people waste money on expensive video cables. They're trying to make up for even more expensive hardware problems!
Usually they fall for the sales babble.

Video prices are so competitive with every one pricing with low margins (10 points in video is common at 'street' prices) that the only way to bring the GP (gross profit) back up is on the really high margin items like cables and extended warranties.

The big box guys are really bad for this as they are advertising with low margins and then putting huge pressure on the sales force to add on the high margin stuff. Like you really need a $400 power bar, er power conditioner, to plug everything into.

[DRBUZZ0]

I can tell you this from my experience (which admittedly is less than scientiffic):

The really thin aluminum-core OEM cables which come with most components are crap. I've hooked them up along with better cables and switched between the two. Yes, there is definately a difference.

The slightly better cables, do sound better.

The lower-end of the higher grade ones (IE: the ones where you start to see metal connectors instead of the plastic ones and they are thicker). They seem to make a difference, some of the time. Probably not much of a difference with low end stuff. However, you can hear a difference on better stuff. This is especially true for longer lengths.

The stuff higher than that, you'd be really hard pressed to hear a difference. Perhaps if there is a very long run of cable or if there is a lot of noise from nearby electronics. But generally...no.

Sometimes it's worthwhile to spend a little more on cables for durability and such, but don't expect to hear much difference.

As for the super high end stuff. The like ultra high end. Well...you can tell the difference if you hook it up to a good oscilloscope and send various waveforms on it. Or if you hook it up to an impediance analyzer. Other wise...it is highly unlikely it will hear any difference.

One thing to keep in mind as well: Try to avoid lots of adapters/splitters/couplers and such. Those can cause you problems

[kevin]

i believe gold is typically used in connector ends because they don't oxidize. copper and silver are both better conductors but oxidize (using copper inside the cable doesn't matter because there isn't any oxygen and surface oxydiation doesn't really matter on a cable -- just the surfaces where contact with a connector is involved.)

BTW, on the shielded cables -- what exactly is being shielded? I imagine most of the electrical noise in a typical house is going to be 60 Hz or maybe 2.4GHz stuff from wireless networks --not the typical ranges for video cables. It's not like I'm planning on running my video cables around the microwave a few times. (I also thought the shielding only being connected on one side was for long runs where a voltage differential might exist between the grounds on each end.)

[ktesibios]

Whoever decided that the standard analog video interface should be unbalanced and use the shield to conduct signal current has earned a high place on my list of People Who Get Shot When the Revolution Comes. Ground loops do cause problems in video circuits and very often the only solution is to buy rather expensive video isolation transformers to break the loop.

In the audio world, mucking around with lifted shields in cables would be unnecessary if equipment manufacturers would just follow a few rules:

1. The internal 0 volt "ground" reference of a piece of equipment should be connected to the enclosure at one and only one point.

2, All inputs and outputs should be either differential or transformer isolated and floating.

3. For non-isolated differential outputs, the source impedance measured between each signal pin and ground should be equal.

4. Inputs should have a relatively low differential input impedance and the highest common-mode input impedance possible. This minimizes common-mode to differential conversion and is where a well-designed input transformer really shines.

5. Cable shields should connect to the equipment enclosure and not to the 0 volt reference.

6. A cable shield is an extension of the enclosure. Its purpose is to provide an equipotential surface around the signal conductors to prevent capacitive coupling of interfering signals to the signal conductors. It should never be used to carry signal current.

And as long as we're dreaming, I'd like a pony and an ice cream soda.

In the real world where these conditions don't apply, lifting shields is sometimes necessary to avoid problems with ground loops. Which end the shield should be connected to depends on the output and input circuits.

If the output is unbalanced or electronically balanced, so that the signal on each pin is referred to ground, current is coupled to the shield via the distributed capacitance between the signal conductors and the shield. Connecting the shield at the source end allows the current to return to its source by the shortest possible path. If the shield is lifted at the source end and connected at the receiving end, this current will find its way back to the source via the grounding connections on the two pieces of equipment. This might not be a problem in a home A/V system, but in a control room with a typical star grounding system that can be a very meandering path. Letting signal current flow in your grounding system can cause bizarre crosstalk problems, e.g. "why the @#$% do I hear SMPTE on the lead vocal?". (More egregious and entertaining versions of this can be had by unbalancing a differential or servo-balanced output by shorting one leg to ground at the receiving end of a cable, as when connecting a third-generation multitrack to one of the old M-series Dolby A racks or patching SMPTE directly from the machine output to a device with an unbalanced timecode input.)

OTOH, with a floating output it's best to lift the shield at the sending end and connect it at the receiving end.

Rane Corp has put out a number of very good technical papers about grounding, shielding and interfacing audio equipment. Check their Web site. If you can somehow find a copy of the tech manual for the old MCI JH600 series consoles, there's also a very informative treatment of dealing with cable shields in that. The manuals for some of Orban's gear also discuss this and Don and Carlolyn Davis' Sound System Engineering 2nd edition is another good resource for sound system signal wiring.

And about those "magnets"- it sounds like you're describing the ferrite isolators commonly found clamped around the ends of cables nowadays. While these are made of a ferromagnetic material, they aren't magnetized and it would make no difference if they were. The effect of passing a conductor through one is to introduce a small, low-Q series inductance in the conductor which helps in suppressing RF interference.

[geni]

Gold-plated plugs do make the best connections over time, when connected to gold-plated connectors.


What kind of timescales are we talking here? Months? years? decades?