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Overview: Most AV cable is made from copper. You may come across silver cables here and there, but copper is generally a better AC conductor than silver by a wide margin. Purity is important. The purer the copper, the better the conductivity, and as a result, the better the cable.
The least pure refined copper, (ETP or “electro tough pitch”) is used in copper pennies and ordinary house and appliance wiring. At the other end of the spectrum, OFHC copper (oxygen free high conductivity) is at least 99% pure. The purest copper known to exist is 99.99997% pure, and is several times more expensive than silver. It’s these higher grades of copper that are used for quality audio/video cabling.
Impurities, like oxygen, can interfere with the ability of the copper to transmit electrical fields without distortion. Copper, like all metals, is composed of metal crystals. The oxygen in a copper cable will form copper oxides (copper “rust”) at the junctures of adjoining copper crystals. These oxides act like little diodes, limiting and scattering low-level signal transmission. Higher frequency signals, like luminance, tend to propagate along the outside of the cable, and as a result, are more immune to distortion. Lower level signals are generally colour information, can be affected, so for bright, vibrant colour, it’s very important that you use cables made with a high quality copper.
Cable Selection: There are several schools of thought when it comes to cabling your home theatre. One cable manufacturer would have you spend as much on cables (“interconnects”) as you’ve spent on the most expensive component in your home theatre. Obviously, it’s in their best interest if you do that, but a budget of 2-5 thousand dollars for cables alone, at the end of the day, just doesn’t make sense. The reality is that you don’t have to spend a fortune on cable. Phoenix Gold and Monster Cable are both excellent choices. Our personal pick for most applications is Phoenix Gold, given their excellent quality and good price point.
Where cable designs differ most significantly is in insulation. Most manufacturers spend a great deal of energy developing insulations that deflect exterior noise while protecting the integrity of your video and audio signal. As with most things, you rapidly arrive at a point of diminishing returns. It’s important to remember that most of the design improvements, after a certain point, protect and maintain frequencies in your AV signal beyond your systems ability to take advantage of. You can, in fact, have too much of a good thing.
Cable Length: The best way for you to get the most from your cables is to keep them as short as possible. We recommend not going above 25 feet without some kind of powered booster. Cable runs over 25 feet, are possible, but we recommend using something like the CELabs 400Comp, a distribution amplifier and signal booster for analog HD, or the Gefen ext-hdtv141 DVI Repeater for digital HD. The longer the cable, the more that cable behaves like an antenna. Also, the cable insulation will begin to absorb the signal. You’ll see all of this as noise and reduced color vibrancy.
There are some peculiarities with DVI/HDMI that are worth mentioning. I’ve heard from many customers that a 20 foot plus cable run, without some sort of line amp, is impossible. The HDCP carrier drops out, leaving your display with video information it can’t decode. As a result, under these circumstances I always recommend spending the extra few dollars for some kind of signal booster.
Reprinted from Wikipedia
Composite video is the format of an analog television (picture only) signal before it is combined with a sound signal and modulated onto an RF carrier. It is usually in a standard format such as NTSC, PAL, or SECAM. It is a composite of three source signals called Y, U and V (together referred to as YUV) with sync pulses. Y represents the brightness or luminance of the picture and includes synchronizing pulses, so that by itself it could be displayed as a monochrome picture. U and V between them carry the colour information. They are first mixed with two orthogonal phases of a colour carrier signal to form a signal called the chrominance. Y and UV are then added together. Since Y is a baseband signal and UV has been mixed with a carrier, this addition is equivalent to frequency-division multiplexing.
Composite video can easily be directed to any broadcast channel simply by modulating the proper RF carrier frequency with it. Most analogue home video equipment records a signal in (roughly) composite format: LaserDiscs store a true composite signal, while VHS tapes use a slightly modified composite signal. These devices then give the user the option of outputting the raw signal, or modulating it on to a VHF or UHF frequency to appear on a selected TV channel. In typical home applications, the composite video signal is typically connected using an RCA jack, normally yellow (often accompanied with red and white for right and left audio channels respectively). BNC connectors and higher quality co-axial cable are often used in more professional applications.
In Europe, SCART connections are often used instead of RCA jacks — though SCART can also carry far superior RGB component video signals (and to a lesser extent, S-Video), so where available, RGB is used instead of composite video with computers, video game consoles, and DVD players.
Some devices that connect to a TV, such as videogame consoles (and the ubiquitous home computers of the 1980s), naturally output a composite signal. This may then be converted to RF with an external box known as an RF modulator that generates the proper carrier (often for channel 3 or 4 in North America, channel 36 in Europe). The RF modulator is preferably left outside the console so the RF doesn't interfere with the components inside the machine. VCRs and similar devices already have to deal with RF signals in their tuners, so the modulator is located inside the box. Also, most early home computers usually employed an internal RF modulator.
The standard connection for composite video is a yellow RCA type plug
The process of modulating RF with the original video signal, and then demodulating the original signal again in the TV, introduces several losses into the signal. RF is also "noisy" because of all of the video and radio signals already being broadcast, so this conversion also typically adds noise or interference to the signal as well. For these reasons, it is typically best to use composite connections instead of RF connections if possible. Almost all modern video equipment has composite connectors, so this typically isn't a problem.
However, just as the modulation and demodulation of RF loses quality, the mixing of the various signals into the original composite signal does the same. This has led to a proliferation of systems such as S-Video and component video to separate out one or more of the mixed signals.
Composite video is often designated by the CVBS acronym, meaning either "Color, Video, Blank and Sync", "Composite Video Baseband Signal", "Composite Video Burst Signal", or "Composite Video with Burst and Sync".
- NTSC composite monitors are semi-compatible with PAL signals, but offer black and white picture even if the signal is in color, and it has poor vertical hold.
- Almost every device with an S-video input or output also has a composite input or output.
- It is commonly believed that composite video is a retronym coined after the introduction of S-video. However, this is wrong.
A standard 4-pin S-Video cable connector, with each signal pin paired with its own ground pin.
Reprinted from Wikipedia
Separate video, abbreviated S-Video and also known as Y/C (or erroneously, S-VHS and "super video") is an analog video signal that carries the video data as two separate signals (brightness and color), unlike composite video which carries the entire set of signals in one package. S-Video works in 480i or 576i resolution.
Y/C signal comparison between composite (a) and S-video (b).
The luminance (Y; greyscale) signal and modulated chrominance (C; colour) information are carried on separate synchronized signal/ground pairs.
In composite video, the luminance signal is low-pass filtered to prevent crosstalk between high-frequency luminance information and the color subcarrier. S-Video separates the two, and detrimental low-pass filtering is unnecessary. This increases bandwidth for the luminance information, and also subdues the color crosstalk problem. The infamous dot crawl is eliminated. This means that S-Video leaves more information from the original video intact, thus having a much-improved image reproduction compared to composite video.
Due to the separation of the video into brightness and colour components, S-Video is sometimes considered a type of component video signal, although it is also the most inferior of them, quality-wise, being far surpassed by the more complex component video schemes (like RGB). What differentiates S-Video from these higher component video schemes is that S-Video carries the colour information as one signal. This means that the colours have to be encoded in some way, and as such NTSC, PAL and SECAM signals are all decidedly different through S-Video. Thus, for full compatibility the used devices not only have to be S-Video compatible but also compatible in terms of colour encoding.
Today, S-Video signals are generally connected using 4 pin mini-DIN connectors using a 75 ohm termination impedance. Apart from the impedance requirement, these cables are equivalent to regular mini-DIN cables (like Apple's ADB); these cables can be used for S-Video transfer if no other cable is available, but picture quality may not be as good.
The mini-DIN pins, being weak, sometimes bend. This can result in the loss of color, or other corruption (or loss) in the signal. A bent pin can be forced back into shape, but this carries the risk of further damage, or even the pin breaking off.
Before the mini-DIN plug became standard, S-Video signals were often carried through different types of plugs. For example, the Commodore 64 home computer of the 1980s, one of the first widely available devices to feature S-Video output, used an 8-pin DIN connector on the computer end and a pair of RCA plugs on the monitor end. The S-Video connector is the most common video-out connector on laptop computers, however many devices with S-Video outputs also have composite outputs.
S-Video can be transferred through SCART connections as well. However, it was not part of the original SCART standard, and not every SCART-compatible device supports it for this reason. Also, S-Video and RGB are mutually exclusive through SCART, due to the S-Video implementation using the pins allocated for RGB. Most SCART-equipped televisions or VCRs (and almost all of the older ones) do not actually support S-Video, resulting in a black-and-white picture if attempted to use, as only the luminance signal portion is used. Black-and-white picture in itself can also be a sign of incompatible colour encoding, for example NTSC material viewed through a PAL-only device.
A hack exists to possibly attain color on devices that do not support S-Video through SCART. This is done via joining the pins 15 and 20 in the SCART connector (either directly or using a 470pF capacitor), and may not yield optimal results.
Pin numbers (looking at socket):
Pin assignments |
Pin |
Name |
Function |
1 |
GND |
Ground (Y) |
2 |
GND |
Ground (C) |
3 |
Y |
Intensity (Luminance) |
4 |
C |
Color (Chrominance) |
S-Video is commonly used in USA, Canada, Australia and Japan, found there on consumer TVs, DVD players, video tape recorders and game consoles. Almost all TV-out connectors on graphics cards are S-Video, even in Europe, where the standard failed to make a significant impact due to the preference of the higher-quality RGB signal (SCART.)
Because it is very simple to convert S-Video to composite signal (just the logical merging of the two through a filter capacitor is required), many electronics retailers offer converter adaptors for signal conversion. No conversion will improve image quality, but will allow connecting to otherwise-incompatible devices. Converting composite signal to S-Video is a little harder.
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