Let's look at component video cables (1 Viewer)

Chu Gai · Aug 24, 2003

The purpose of this post is to take a look at cables that can be used as component cables from the point of view of bandwidth. A discussion of this will also include some additional bandwidth comments regarding associated devices.

Often the topic of what component cable should I buy is asked. The likely responses will be brands or particular vendors. I find this information generally useless and while everyone may indeed be correct, it doesn't address the fundamental question of what are the requirements needed to successfully pass a signal from one area to another such that it can be effectively used. Note that this does not mean which cable has the least amount of attenuation. While buying such a cable in not a bad thing, often in cases where the lengths are very nominal, a few meters, it's completely unnecessary and results in a gross overspecification that doesn't result in a visible difference. In the situations where there may be a visible difference such as in long lengths, often a slight adjustment on the display device restores everything to the original level of acceptability. When that's done, no visible difference is seen. We've all seen TV's in stores and it's nothing short of amazing how different many brands can look. Too much red, not sharp enough, contrast is off, etc. Most of us go to the trouble of adjusting our sets using calibration disks to provide references and targets. Some even go so far as to enlist the services of a calibration professional. It's quite reasonable to expect that given a long length of cable one may have to adjust their TV sets. If you find this disturbing then just buy the widest bandwidth, heaviest shielded cable you can. Personally, periodic calibration after making changes I consider just the way things are. In the scientific fields it's Standard Operating Practice and given that the differences are generally small, no one makes a big thing about it. However, audio, if nothing, is about raising trivialities to the level capital offences.

Bandwidth is generally defined as the point at which a signal of a particular frequency is down 3 dB. Being down 3 dB means that we've lost 1/2 of our signal. Generally, but not always, this is taken at a distance of 100 feet. Hence, when a vendor specifies this, it'll generally read something like "bandwidth of 750 MHz @100 feet". When a vendor doesn't specifiy bandwidth but instead specifies just the number you're at a loss as to what they really mean. You should contact the vendor to get clarification.

So what are the problems associated with insufficient bandwidth? Well if the signal you're pushing through has a bandwidth of 5 MHz and some device in the middle has a bandwidth of 2 MHz, then most certainly that device will severely attenuate or chop out the signal above 3 MHz. You'll be losing information that may well not be compensated for by adjusting controls on the TV. Fine detail will be severely compromised. Kind of like clipping if you will. Receivers or other processing devices that allow video switching should have a bandwidth specification. Depending upon what's plugged into the device, the bandwidth may be adequate, marginal, or simply deficient. I take the manufacturer's specification to mean that it will attenuate the value by 3 dB. Various values that I've seen here are 50, 100, 200 MHz and there are no doubt others.

So what bandwidth is necessary in order to pass these signals? Our eminently capable Bob McElfresh has posted the following information before.

Part #1694a solid copper 18 AWG Foam HDPE insulation
Capcitance:16.2 pF/ft @ 1 MHz
10 MHz:417 feet
67.5 MHz:191 feet (no value for 50 MHz from Belden's website)
100 MHz:163 feet

So how good is Radio Shack's 15-1563 cable? Well we know (I know because they sent me the information regarding this cable) that they use a stranded copper with an effective gauge of 20 AWG. That's somewhere between the RG59 and RG6. If we shade it towards the lesser performing cable we see that the RS product is a very good performer that vastly exceeds our requirements.

So what does all this information suggest? Well an examination certainly indicates that the thicker the center conductor, the longer the run can be before you get 3 dB down. It also suggests that within a particular gauge there's not a whole lot of difference in the length before one get's 3 dB down. It also suggests that even quite thin cables are emminently usable if the lengths aren't too long. For example, let's look at the 30 gauge and contrast it to the RG-6 for a 2 meter or a 6 foot run. That's pretty typical. Well if we're running progressive out of our DVD and using the 3-times rule, we'll be considering the 50 MHz values.

RG-6 down approximately 0.09 dB
30 AWG stranded down approximately 0.34 dB

So is the RG-6 better? Would we expect to possibly see a major or a minor difference? Well consider that many people arbitrarily use splitters if not multiple ones for their cable TV's and report entirely satisfactory performance. Aside from a trivial insertion loss a 1:2 splitter is going to cut your signal in half. In other words a 3 dB loss. How much of a loss is there with 0.09 dB or 0.34 dB? Percentage wise it's 2.09% and 7.25% respectively. Don't forget, that's at 3 times the expected signal you're going to be sending. Given that seeing the difference between SVideo and component can be pretty tough for people, I think a 5% change is going to be damned tough. And if you adjust your TV I dare say it'll be next to impossible to pick one from another with any degree of reliability.

So are there reasons to choose one cable over another for a relatively short length? Well sure. If you've got an interference problem you can't figure out where it's coming from, you just might want to go to a quad shielded RG6 or RG59. Maybe you don't like molded connectors. Maybe you don't want to futz with your TV (surprising from audio and videophiles though!). Maybe you just want to overspecify (you could be the sort of person for whom distilled water isn't good enough for your steam iron and you get 18 megaohm water from the lab). Flexibility may or may not be important to you. Maybe you're a solid center conductor person. Maybe you like stranded. Maybe you've got it in for Radio Shack. Maybe you think that cable looks cheesy or this cable's RCA don't cut it for you.

From the point of view of perceivable performance though, maybe it just doesn't matter. As careful as we want our children to be with their possessions we can be quite destructive to cables. We'll bend them, step on them, pull on the cable instead of using a gentle twisting motion to remove the RCA, we won't perform any kind of periodic maintenance that looks like cleaning the connectors, and then one day we'll notice interference or some sort of a bad picture. We won't damn ouselves, but we will damn the cable. We'll come to this forum, to that forum, and we'll buy the best cable that's out there and voila, all the problems have gone away. We'll sing the praises of this new cable, and brother, sing you better after you've dropped a hundred or more. Yes there's a no questions asked return policy but having to eat s/h both ways and probable insurance charges can quickly put a damper on your enthusiasm.

So how much do you or should you pay? Well if you're a fan of the 10% rule, knock yourself out. If you're into specifications and popular brands then buy the highest spec'd cable you can. If you're into buying a cable that can do the job and then some and you're running a couple of meters or so well you just might find there's a whole bunch of places on the web selling 100 megahertz cable that's 3 dB down at 100 feet. A couple of meters is somewhere around $10. Yes $10. Why so cheap? Well it's mass produced for one. The manufacturer isn't advertising and instead selling to resellers. It's being made using cable from lesser known (sometimes even well-known) companies but they're buying a couple of million feet. Costs go down you know. Yes it's 75 ohms. Maybe the question is why are some companies charging so much?

Click to expand...

Mark Rich · Aug 24, 2003

With this kind of posting I'm glad I'm not the cable maker sponsoring the forum.
First I dont buy the 'cables is cables' theory because I've actually tried more than a few cables and kept an open mind while doing so.
Its also getting tiring reading these kinds of postings. Hardly surprising that other forums have put a stop to them.

Chuck Watwood · Aug 24, 2003

Chu,

Thanks for the detailed post. I appreciate the information.
Well informed consumers make better choices and that includes audio/video consumers. My experience is that most salespeople, especially at places like Best Buy and even at high end audio/video stores, don't know what they are talking about. The information is appreciated.

Thanks,

Chuck

PaulT · Aug 25, 2003

With this kind of posting I'm glad I'm not the cable maker sponsoring the forum. - Hardly surprising that other forums have put a stop to them.

Does that mean other forums are bending to their advertisers wishes to stop informative posting of data to those who need to make decisions on which cables to purchase ??

Some buy into one theory (cables is cables), others feel they can tell a difference. Posting information from both sides is allowing the readers to decide on their own. Really what purchasers need to do is try their cable choices side by side and see if they can find differences. Don't see too many salesman setting up that scenario 'in-store'.

I have also tried various cables over the past 27 years starting from 2 channel audio systems and have come to 'my' conclusion that an 'open mind' sometimes equates to an 'open wallet'.

Click to expand...

Chu Gai · Aug 25, 2003

When you've got two drivers, last race of the Winston Cup, and first place for either driver means you've won and with that comes all the money, all the advertisements, all the glory and the little hedonistic perks, a 1/100 of a second means everything. Second just makes you a trivia question.

I think it's prudent to define your problem and choose according to your needs and by all means if you wish to spend more, then do so. If you think engineers are full of crap with the 3 times rule make it 4 or 5 times. In either event you'll be able to develop your own short list knowing full well that each of the choices is up to the task. Then weed them out as you see fit.

KurtBJC · Aug 25, 2003

Just a couple of notes on this...I think, Chu, that your comments are in general correct, but there are a couple of quibbles I have.

First, I think that a factor you do want to take into account is impedance tolerance--especially when you're getting into HD video where frequencies are high and wavelengths are, therefore, comparatively short. A 35 MHz signal has a wavelength of 8.5 meters, and so a cable, to be a quarter wavelength long (where the significance of correct impedance starts to become really critical) needs only to be about 2 meters. A lot of manufacturers don't publish impedance tolerance specs, and so you don't really know whether "75 ohms" means 75 ohms +/- 5 ohms or +/- 1.5 ohms, or what.

This is important because in most applications, plain old attenuation isn't going to be the problem, but loss of image quality due to signal reflection caused by impedance mismatch may start to factor in--especially for people who are doing long runs to projectors.

This tends to favor the larger cables, because it simply is easier to keep tight impedance tolerance in large cable.

The comparison you make to a CATV signal splitter is, I think, not really apt. The problem with the comparison is that a TV tuner is designed to handle signals over a very wide range of amplitudes, so a few dB isn't a problem. The guy who lives a mile from the broadcast tower and the guy who lives 25 miles away are getting signals that are about 25 dB apart, but both should be able to get excellent reception if they have good lines of sight and good receivers--heck, on shortwave I listen to things that are coming from thousands of miles away, but I can tune down to the AM band and listen to stations two miles away. But the component video inputs to a display aren't like a tuner--they're not designed to pick up signals over that kind of amplitude range, and are "expecting" something on the order of a standard video line level signal.

Second, I'd take issue with the notion that if you need really good shielding, you want a quad-shield cable. The transfer impedance (i.e., the effectiveness of the shield in rejecting RFI) of a quad-shield cable is significantly inferior to that of a modern precision video cable with a high-coverage copper braid; I don't have Steve Lampen's latest book right in front of me, but he's done a table which shows the difference in transfer impedance for various shield configurations at various frequencies, and it's surprisingly large.

The tendency here is to assume that quad shield has four shields--and therefore must be better than a cable with two or three shields. But it's not just a matter of number of shields. The 60%/40% aluminum braid combo seen on most of the quad shields only gives a total of 76% coverage, and the conductivity of the shield is lower which results in a less effective path for noise to ground.

Anyhow--good post, and very analytical. It's very hard, I think, to tell in principle just when cabling is going to make a difference in any particular application because there are so many variables.

Chu Gai · Aug 25, 2003

Well KurtBJC, as I stated in the original post, I limited my discussion to attenuation losses only. I have every intention of addressing impedance shortly and getting into matters such as you're mentioning. FWIW, if you're a nut (not in a bad way) about impedance then you owe it to yourself to look at Belden's conformable cable. I will say that one thing us consumers overlook or arent' aware of, is as good as we think our set are, HDTV, doublers, and all that, by no stretch of the imagination do they reach the level of a research grade monitor. I've heard, but not confirmed, of an individual that took various lengths of shielded power cord and made video cables from them. I think, through coupling he wound up with a net length of over 30 feet. Neglible differences were seen between that monstrosity and a couple of meters of good quality coax. I'm looking to find out the details but not making out very well. If true, this would suggest that for consumers, with nominal lengths perhaps greater than a couple of meters, this is a very over-blown issue. There's more to impedance than what you're touching on. Like I said, I'm working on it!
The shielding issue is further down the road. But again keep in mind, just 'cause it's maybe got 96% shielding doesn't mean it'll make any difference in a home application from something that's considerably less shielded.

KurtBJC · Aug 25, 2003

Understood--but since your discussion also was more generally to "bandwidth," it seemed to me that impedance, which is definitely frequency-dependent at least in the sense that it will come significantly into play in sufficiently long cable lengths--those lengths, in turn, depending upon frequency-- was relevant as well.

As for shield effectiveness--it certainly may not come into play in a lot of applications. It's one of those very application-dependent issues, where one user's major RFI issue demands good shielding while another user won't see the difference between very well-shielded and very poorly-shielded cable. Sometimes, though, it does surprise me to see just how much difference it can make. A year or so ago, my brother had a major problem with off-air signals getting into his CATV lines (see, now it's my turn to bring RF applications into the discussion...

) Anyhow, we replaced a rather large amount of generic CATV coax with 1694A, and the problem was nearly gone--it really surprised me, because I've seen so many times where badly-shielded TVs and VCRs were the real culprits, and I figured we'd get at best a modest improvement in the off-air interference. Sometimes you really can't tell whether you've got a shielding issue until you just go and pull some cable and see what happens.

Bob McElfresh · Aug 25, 2003

Its also getting tiring reading these kinds of postings. Hardly surprising that other forums have put a stop to them.

When the arguments start looking like personal attacks, we shut the threads down as well.

But I feel strongly that we need a fourm to discuss the technology and science behind cables and wires. Otherwise, people may believe that a $300 component cable is needed for their $500 TV. There are powerful marketing forces that encourage this type of thinking.

Please, contribute with what knowledge you have and keep the discussion about the science, and not attack each other.

Click to expand...

Mark Rich · Aug 25, 2003

Careful Kurt.
When Chu is finnished with this thread I think a lot of people will be returning those overpriced, thick and heavy cables you sell and then buying generic cables from RS and Target

Chu Gai · Aug 25, 2003

Heck I don't see why Brian. Maybe people will go out and buy a set of nominally priced ones and use them as backup. Keep in mind, I'm not stating a person can't have a preference for overspecification.
As far as the shielding story you touched upon Kurt, did you guys ever figure out the source of the problem? Also did you guys ever consider using one of those 'hum' eliminators like from Jensen, Mondial, etc. to simply break the ground?

DaleBesh · Aug 26, 2003

I have SEEN a difference in the image between a Monster and Bettercable S-Video cables. After repeated A/B tests the difference was always there.
The Bettercable was noticably better. Now, if I left the room and someone switched them, I would not be able to tell which was being used. So the difference was not major, but the fact there IS a difference that can be perceived in standard 1M cables, is significant in my opinion.
I have bashed BCs in another audio thread for inferior workmanship. So sticking to one 'brand' is not necessarily the answer. I use a Monster subwoofer cable because of what I think is a superior overall design for that application.
It can be very easy to generalize.
If you make your own and can be consistent in the fabrication, use quality materials, and you are fairly well skilled, that could erase a lot of doubt about differences I would think. Although home construction of an S-Video cable might not be that easy.

KurtBJC · Aug 26, 2003

I don't find this sort of discussion threatening at all; it seems to me that a lot of what people do in home theater is in the general nature of "overspecification," and with video cable, what one really wants to know is that the cable isn't the source of trouble. The tighter the specs and the better the build, the more secure that knowledge is; but one really never knows in advance when or if a major difference in performance will come from a particular swap-out. When one is selling cables, one really can't honestly tell a customer, for example, "you will see deeper blacks, better color and higher resolution with this cable." How could a statement like that ever be justified without plugging the darned thing in to the customer's system and having a look? But what one can tell people, in all honesty, is that the product meets or exceeds very tight specs, is well-made, and is ideally suited for the application at hand. In some applications, something less theoretically ideal might do just as well; in others it won't; and which of those categories a particular application will fall into can be hard to predict.

On the shielding you ask about, Chu: I think maybe you're asking about something different. The scenario I mentioned above was strictly an RF CATV application, and we weren't getting any hum in the system--the only issue was off-air signals getting into the cable and interfering with the cable reception. Swapping out the coax for the more heavily shielded 1694A, in that situation, eliminated perceptible off-air interference on all but one of the channels involved, and reduced it on that one to a watchable level.

If what you're asking about is our audio cable hum rejection scenario, no, we didn't try using an isolation transformer--and in the case of induced hum, that wouldn't work in any event. We have used them to deal with ground loop hum, and they do work nicely.

Mark Rich · Aug 26, 2003

Kurt,

Can you see any difference between a decent generic component video cable ($10-15)and the cables you sell (1694a etc.)?
Have you have compared the cables you sell to popular retail cables? If yes, which ones and what were your findings?

Chu Gai · Aug 26, 2003

well keep in mind something i said earlier Dale which had to do with making minor adjustments to one's tv set. i've a sneaking suspicion a nudge here or there and things are back to normal. i fully appreciate the difficulty in determining which is which when the evaluation isn't time-proximate. sure if the differences are large it's a piece of cake. when small, near impossible. i'd think though that one could pick up a switcher with adequate bandwidth and have someone do the switching.

must've been one heck of a transmitter causing those problems. I'd heard of a similar story. The corporation responsible for the tranmitting tower was informed of what was going on...bursts of noise that got into a person's system. The company was very proactive, I guess, as they realized this shouldn't have been happening, and detmined they had a grounding problem somewhere. It was fixed rapidly as being that they were dealing with high power, there was a very distinct possiblity that the poor ground was an issue for human safety.

Chris Hovanic · Aug 26, 2003

Chu Gai... I appreciate your information and your past replys to my posts as well as others.

I was wondering what your background is? Where did you learn all of this stuff? Its hard to debate someone with a Masters or PHD or 20 years experience (or all 3) in the Electronics field.

Discussing some of these issues with a electronics guy at work and his responses are very similar to yours which makes me believe that you are accurately explaining your topic(s) of choice. Now if I just had an expert in 23 other fields (including women

) I would have it made!

Thanks Again.

KurtBJC · Aug 26, 2003

I've done casual--that is to say, non-scientific, non-controlled--comparisons with various generic cables, mostly stuff that came packed with equipment (none of the popular RS or similar stuff), and it has seemed to me that even at short run lengths, I saw better image definition using Belden 1694A cables. But I don't really like to rely on subjective impressions that were garnered using a particular display and source--my view has always been that the measurable properties of cables are the best place to look for comparison.

DaleBesh · Aug 26, 2003

Chu, I can appreciate being aware of other variables.
My observation was on a calibrated display. Changing out the 2 standard MC and BC cables was the only variable.
What I saw with the BC was slighlty more saturated color, and an increase in sharpness (not edge noise).
Slight, but still noticable. This was done over a span of a few mintues with a DVD playing.
Could the Monster cable have been defective? Of course. But not to the point of not being fully operational, something subtle. The only other observation was better pin retention with the Bettercable, and it is unlikely that was a factor because then I would expect some variability in the results every time I connected the MC.
I am in no way generalizing this observation to say one cable is better than the other, unless I could repeat it with a greater number of each cable type. I will say the change was an improvement, to my eyes, which is a little more than just something 'different'. Again, what I saw was not significant, but repeatable. In the scheme of things it is not relevant, except to say if there are to be slight differences in cables, visual observation would make those much more apparent for video cables, than listening does for audio cables, barring problems related to grounds/noise in either case.

Chu Gai · Aug 27, 2003

Entirely possible Dale however as you pointed out, you knew the identity and you were watching for a while. Is this really the best way to determine a difference? I think not. A better, if not arguably the best, approach would've been to use a switching device where someone did the switching and you focussed on a particular image or series of images. Those images could've been test patterns involving lines, colors, anything that would allow your attention to be closely focussed on what the goal of the 'Better Cable' was. Yes, I'm sure there are people that're saying, 'Damned Chu bringing up the old DBT again.' Well yes, I guess I am. But consider that the approach I'm taking is nothing more than what millions of people in this country go through weekly when they go to their eye doctor and are looking to be fitted with lenses. It's not very threatening and really pretty easy to implement. It also doesn't result in an extra cost to the consumer to go with this lens grind as opposed to that one. How annoying would it be for an eye doctor to hand you a set of lenses and say something like, walk around for a while with these and tell me what you think. Well that's the approach that's given to the public in general with cables. Take them out for a spin. Shame shame I say for not telling them the limitations of such an approach.

Conversely, it's somewhat telling, when major manufacturers, and by those I mean ones who have deep pockets for research, don't provide objective data. There's no photographs illustrating differences, no densitometer readings that would corroborate 'bluer blues'. Actually the pockets don't have to be that deep. A decent digital camera (Nikon?) or conventional camera could be used to illustrate improved sharpness. An increased saturation probably would best be served by some sort of densitometer taking readings off the screen. I'd imagine those could be rented or for the more creative entrepreneur, obtained from a variety of sources, via the evaluation routine. Then, the investigator could look at Cable A vs Cable B, see what happens when the set is optimised between evaluations or left alone. Telling information in all cases I'd think.

I know one can't test all the TV's out there and often it's been advanced as one of the reasons why this can't be done. They may say something like each set may behave differently. That's a lot of may's and maybe's to my mind. So maybe we as consumers should be asking why don't magazines like Stereophile step up to the plate. They've got a lot of toys over there. Fear of alienation of advertisers? Well do the major photography magazines have a fear of that when they publish data and measurements taken on lenses? Is Sigma going to take a walk if their lens has worse edge sharpness than say a corresponding Leica? Or is the consumer going to benefit when the photgraphy magazine says something like 'this softness in the edge sharpness can only be seen when we made a 20 x 25 print. For an 11 x 14 it was completely unnoticeable'.? You tell me. The magazine certainly had no problem in optimising the camera/lens parameters to get the best image. Maybe a little bump on one of your monitor settings does the same thing? Is Fuji going to pull it's advertising when the latest incarnation of films shows Kodak to be the best? Or are they perhaps going to look at it and possibly make some emulsion changes and go for one better? Or do they just not care?

My main issues with Monster is they have an enormous tendency to litigate everything. Moreover, they're long on advertising and short on information. Try getting them to tell you the gauge of a particular speaker cable. Sheesh! Maybe I'd have a different opinion if I had a vested financial interest in the company.

A few, if not one, meters of cable is what many of us need. I don't think they're that hard to make and that hard to find for a fairly inexpensive price. Sometimes you know, the money you save from going from the 10 or 20% rule on cables to just buying a cable that does the job might mean the difference between one monitor and another, one set of speakers vs another. Maybe?

Chu Gai · Aug 27, 2003

To illustrate how our eyes, and yes that includes the brain and all that, can have issues and are not the perfect arbitrators, check out the following link.
http://www.grand-illusions.com/square.htm

In fact, check out all the links at that site. Lot of fun. Not as much fun as seeing the Lakers lose, but hey!

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