AV Cables Basics
Guide to Video Cables
Short guide to analog and digital video cables
Are you confused by the variety of video cables found in home entertainment and home theater applications? Do you know what is the difference between composite video and component video, DVI and HDMI, or in that case, what is the difference between analog and digital video interconnects?
Help is on the way! This easy-to-follow AV cable guide explains all there is the need to know about the most common video interconnects used in home theater system components.
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An Introduction to Video Cables
Video Cables are available as either analog or digital interconnects, with the majority of analog video interconnects being based on the same type of RCA or BNC connectors found in home theater sound systems.
On the other hand, digital video cables use different types of connectors. Up to very recent, the most common digital video interconnects were i.LINK and DVI; however, these were soon superseded by a new digital standard—HDMI—that carry both video and audio over the same cable. These digital interconnects were developed to support the higher speeds required for the transfer of digital high resolution video information.
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Audio vs. Video Cables: Same end connectors but...
We stated that most analog video cables use the same RCA or BNC connectors found on audio cables. However, this does not imply that audio cables can replace video interconnects. Because of the higher frequencies involved in video information, video signals are more susceptible to degradation as a result of radio frequency (RFI) and electromagnetic interference (EMI) than audio signals.
Even more so are HDTV signals; these signals carry much more information than a standard-definition video signal, leading to even greater constraints on video performance and bandwidth response.
The use of substandard video cables would not only affect picture clarity due to possible insufficient bandwidth response of the interconnect cable, it will also result in lines, 'snow', and other artifacts on your TV screen as a result of interference effects.
As such, home theater cables designed to handle video signals have to be engineered specifically for the purpose. One cannot simply exchange video with audio cables even if the end-connectors are the same.
The use of double shielded interconnects using both braided copper and metal foil, with high quality 'silver-plated' inner conductors and 'gold-plated end connectors', is almost a pre-requisite in quality video cables to preserve the strength and accuracy of the original video signal.
Analog Video Cable Types
Most common video cables are equipped with at least one of the following types of connectors (listed in order from lowest-quality signal transfer to highest):
The SCART connector is mainly found on systems designed for the European market. In addition, do not expect to find all of these connections present on all of your system components; in particular, S-video connectivity is being phased out by most HDTV makers.
Furthermore, today's slim HDTVs often call for use of proprietary mini-type connectors that interconnects with specially designed break-out cables to enable the HDTV to interface with standard AV cables. This is mainly the case with composite and component video outputs which often make use of the same connector on your TV and then connects to your equipment via a breakout cable.
'Coaxial' is a type of cable where the signal carrier (inner conductor) and its shield are aligned along the same axis (generally a signal wire runs down the middle of a cylindrical shield).
This is not a purely video interconnect in that it is mainly
used for connecting antennas, cable boxes, VCRs, TVs and more. Coaxial RF can carry
both video and audio simultaneously, modulated over a radio frequency (RF) signal.
A dual-shielded RG-6 Coaxial Digital Audio Video Cable from Mediabridge terminated with Pro Grade Nickel Plated F-Type Compression Connectors
Standard coaxial cable is referred to as 'RG-59'. Higher-quality 'RG-6' cable features a thicker internal copper core, lower signal loss dielectric and better shielding (often using double or even quad layer shielding). This makes RG-6 cable better suited for digital satellite TV and long cable runs.
Coaxial cables are terminated with connectors designed to maintain a coaxial form across the connection and have the same well-defined impedance as the attached cable. One such common coaxial connector is the F-type connector shown here. These connectors are usually plated with high-conductivity metals such as silver or gold as this helps to better conduct the RF signal due to the 'skin effect' applicable at these high frequencies.
A Composite Video interconnect from Cables to Go with separate audio connectivity terminated in RCA-type connectors
Composite video cables transmit all signals required for color video including luminance (brightness) and chrominance (color) information over a single interconnect. RCA, F-Type, or BNC connectors are used at each end of a 75 ohm coaxial cable to hook up the video signal source to the display.
Composite video cables normally come accompanied by two audio cables for the left and right channels in stereo sound. Connectors carrying composite video signals are usually color coded 'yellow' and labeled as 'video, CVBS, composite, or baseband'.
Composite Video is standard on all TVs and DVD players.
S-Video (Y/C) provides a better quality picture than composite video. S-video splits the signal into luminance (black and white information) and chrominance (color information). It typically uses 4-pin DIN connectors at each end of the cable and is comprised of two 75 ohm coaxial lines. Most DVD players have an s-video output.
However, as stated in our introduction, this video connection is disappearing fast especially from the latest HDTVs. The slim profile of today's LED and plasma TVs provides a real challenge for designers to make the most of the limited available connectivity space, with the first to suffer was S-Video connectivity in favor of multiple HDMI ports.
Further up the video quality scale is component video. Component Video is capable of significantly better picture quality than composite video and S-video.
Component video cable consists of three 75 ohm coaxial lines with each transmitting one of the three parts of the video signal.
In component video, the color difference signals are mathematical derivatives of the RGB signal in that component video subtracts the luminance (luma or brightness) signal from the subcomponents of the chrominance or chroma signals (blue and red signals.) For this reason, component video is often described as 'Y, R-Y, B-Y' or as 'YPbPr'. This also means that there is no need to transmit the green component as a separate signal since it can be inferred from the 'Y, B-Y, R-Y' combination.
Converting video into luminance and chroma information allows for what is referred to as chroma subsampling; this help reduce the bandwidth requirements.
Component video connections are found on nearly all DVD and Blu-ray players, HDTVs, and video projectors.
Like Component video, RGB video provides excellent picture quality. It is in fact another form of analog component video except that instead of the YPbPr scheme, it uses one of the various RGB video standards (e.g., RGBS, RGBHV, RG&SB) to carry uncompressed video. This also means that it imposes no limit on image resolution and color depth.
The drawback is that RGB video requires a large bandwidth to carry
the video signal, which bandwidth is partly used to carry redundant information
in that each of the color components also carries the same black and white information.
RGB video is mostly found on projector systems, personal computers and HDTVs.
RGB connectivity varies between source components. Most modern computers offer this signal via the VGA port over a 15-pin D-type connector while many HDTVs in Europe provide RGB connectivity via the SCART connector. Irrespective of the connector used, RGB requires a multi-channel video cable to carry the uncompressed video signal between system components.
However, since the advent of HDMI, the popularity of RGB as a high-quality video connectivity is fading fast; rather, HDMI is now the de-facto standard where high-definition video connectivity is required.
Also known as the Peritel connector, SCART is a 21-way connector that supports both audio and video connections.
As indicated earlier on in this video cable guide, this AV connector is use mainly in Europe rather than the US. It can be thought of as an all-in-one AV connector in that it provides for separate composite video in and out connections, RGB video, separate audio input and output connections, as well as a number of control signals.
Typical applications include home cinema, Audio/Video equipment, satellite receivers and Cable boxes, and HDTVs.
For SCART-plug connection details, please check the following webpage at electronics2000.co.uk.
There are three main types of digital video cables, i.LINK, DVI, and HDMI. Note however that both i.Link and DVI were originally developed for use by PCs, while HDMI was specifically developed by some of the major electronic manufacturers for use in consumer electronics products such as DVD players and HDTVs.
Also known as IEEE 1394 FireWire, i.Link is a 400 Megabit/sec high speed interconnect for the transfer of digital information—video, audio, data—between compatible camcorders, computers, HDTV products, etc.
i.LINK ports can use either a 4-pin or 6-pin configuration though most A/V equipment is mainly 4-pin.
The second type of digital video interconnect is the DVI, or 'Digital Visual Interface'. DVI technology was developed to enable high-resolution applications such as HDTV tuners and DVDs, to run on digital flat-panel displays. These applications call for specialized video cables to handle the wider bandwidths associated with High Definition while providing excellent EMI/RFI interference reduction.
For a detailed explanation of DVI cables and connectors, please refer to our DVI Cables Guide.
Short for High Definition Multimedia Interface, HDMI was originally released in Dec. 2002. Since then, numerous versions were released and in the process, it become the 'de facto' standard in high definition video applications.
Its primary advantage over previous digital interconnects (i.Link and DVI) is its capability to carry both digital video and digital audio over the same interconnect—thus eliminating the mess of cabling behind home entertainment centers.
For more information on HDMI, please check our Practical HDMI Cable Guide.
Audio and Video Cables Buying Tip: Always check your equipment to determine the type of supported interconnects before buying home theater cables.