Cables and Signals Unscrambled
One of the most commonly confused topics in home theater speak is the topic of inputs, outputs, cables and the signals themselves. We will try to make this less complex and provide visual aids to help identify the actual input and output plugs you will find.
We need to stress that the signal carried by a cable is not always identified by the cable itself. Thus, calling the signal by the name of any given cable used is a big mistake and can lead to confusion. Let us begin by covering the actual signals used. We will then discuss what cable(s) can be used for a specific signal(s).
Signals, or ways to transmit a video image.
A composite signal is a signal that carries all the separate components of a signal, such as color, gray scale, and horizontal and vertical positions on one single cable. These signals are of the lowest quality since the input device, such as a projector, television, or monitor has to comb (filter) the individual elements of the image out of one signal.
The quality of the image you get depends on a number off variables. These variables include how well the transmitting device — like a DVD player — encodes the signal; how well the receiving display filters out all the needed signal components to reassemble the image; and how much actual information the single cable can carry.
Sending a standard definition NSTC signal via composite cable seriously degrades an already marginal resolution. Sending any signals with higher resolution — like a 480p signal (a progressive scan NTSC image with twice the resolution of standard NTSC video) — is not possible.
A Y/C signal is a specific type of component signal where the signal itself is carried in two parts: the luminance(Y) — or the overall brightness and contrast of an image, and the chrominance (C) — or color in the image.
Because the signal is actually in two parts, it doesn't need to be compressed as much as a composite signal, and on the receiving end, it doesn't need to be filtered twice to regain the original components of the image.
Obviously this signal would need two separate cables, or a single cable with two separate conducting wires shielded from each other to transmit the signal. Because we are now carrying the same signal over two cables, there is a lower occurrence of resolution loss than with a composite video signal. And, even though the signal is now carried over two wires, a Y/C signal is still not used to transmit anything greater than standard definition television.
A component signal is a signal that is carried in three parts. It can be either analog or digital.
In its analog form, it is referred to as Y,Pb,Pr. In its digital form it is called Y,Cb,Cr. (Be aware that these two signals are frequently mislabeled on DVD players).
In either form, the signal is split into its three primary components: Y for luminance, Pb for the blue component, and Pr for the red component. Green (Red, green, and blue make up white light and all other colors) is inferred by the absence of red and blue. Since video is actually recorded as a component signal, keeping it in its native format yields the best results. Component signals are used with all resolutions of video, from NTSC to HDTV.
RGB and its variations
Computers output a different type of signal than video. Generally a computer outputs an RGB type signal.
An RGB signal is not the same as a "component signal," although it is a type of component signal as it actually carries its signal as components of the whole.
Generally an RGB signal is split into five components: RGBHV, red, green, blue, and HV for its horizontal and vertical sync signals. And, what this means is that five separate wires are needed to carry the signal. (On a side note, since it is rarely used anymore, an RGBHV type signal is sometimes carried on four wires as an RGBH/V signal where the horizontal and vertical syncs signals are merged into one, and are sometimes carried on a three cable system. They are and referred to as an RGB sync on green, where the H/V portion is merged with the green.)
The main reason for even mentioning RGB signals is to point out that computer graphics and computer outputs do not comprise a typical video signal, and if you want to convert one to the other you will need some type sort of signal converter. RGB type signals can carry very high resolutions, far exceeding what component video signals carry.
Cables and the type of signals they carry
The term RCA cable actually refers to the type of connector on the end of the cable — not the cable itself. The cable itself is referred to a coaxial cable, meaning a two-conductor cable, in which one conductor forms an electromagnetic shield around the other.
The two conductors are separated by insulation. These cables are, by far, the most common in the consumer industry. The cable can carry either an analog or digital signal and is used for both audio and video signals. The difference between the audio and video version of the cable varies depending on the manufacturer. Given cheap cables, there is probably no difference at all;, with more expensive cables, the video cables will be of a higher gauge copper wire and will have better insulation to negate interference over long distances. The different types of RCA cable configurations are as follows:
Composite:. When a single RCA type cable is used to carry the entire signal, we refer to it as a composite cable. Normally, when you buy a composite cable at a store, it will come with three cables: one that is color coded with yellow for, and two that are color coded with red and white for right and left audio. (See below).
On your video display, the input/output for composite video via RCA type connections will look like this:
We would recommend not hooking up anything via a composite cable. Carrying the entire video signal on one cable degrades the image far too much. (Please note that a composite cable cannot carry a progressive scan image, nor can it carry and HDTV signal of any type. Even if using a progressive scan DVD player, if you output your signal to a display device via a composite cable, the displayed image will be, at best, 480i. If your older VCR only has these types of outputs, consider upgrading to a S-VHS VCR.
Component: RCA type cables are also used to carry a component signal. In this configuration, three separate cables are used and are normally — but not always — color coded red, green, and blue as seen below.
RCA Type component connectors will be found on most DVD players, cable and satellite boxes, and other HDTV receivers. Component cables can carry progressive scan and interlaced signals, as well as standard and high definition video. These cables are recommended for use when hooking up your system to a video display device (if the display is equipped with them). If you are using component cables to carry an HDTV image, please purchase only the highest- quality cables. Low grade cables can hurt horizontal resolution and degrade image quality.
S-video began as a higher resolution alternative to the standard VCR. These "Super" VCR's needed a higher resolution cable to output their higher resolutions; thus and the S-video cable was born.
Think of an S-video cable as two composite type cables wrapped up in one cable, yet shielded from one another. The S-video cable carries only one type of signal, a Y/C signal. Like an RCA type composite cable, it is unable to carry a progressive scan image and is not used to carry an HDTV signal. S-video inputs and outputs are found on higher- end VCR's, all DVD players, most camcorders, and laser disc players. Just about any video source that outputs an NTSC standard definition signal will have an S-video output. If your video source is lacking a component output or any higher resolution output, then we recommend using your S-video output. It will be a vast improvement over an RCA type composite output.
A BNC, also known as the Bayonet Neill-Concelman cable, is another type of coaxial cable. The only difference between an RCA type cable and a BNC cable is the end connector.
A BNC cable actually turns and locks onto the back of your source and display device, making it difficult to accidentally disconnect them. BNC cables are rare on consumer electronics, but are common on any commercial grade video and audio electronics.
A BNC cable can — and does — carry any type of signal. In a single cable form, it carries a composite signal. Yet, when using two cables, it will carry a Y/C signal. Three cables are used for a component signal and a RGB sync on green signal. Four cables are used for an RGBH/V signal and five are used for an RGBHV signal. Any cable type can be turned into a BNC type connecter with simple adapters, or what are known as break-out cables.
The example below shows a BNC type input from a projector. As you can see, the five BNC connectors will input various types of signals, depending on the number of cables you connect and the source(s) you are connecting them from.
Monitor or 15-pin Cables
All of us should be very aware of the 15-pin connector, or as it's commonly called, a monitor cable or VGA cable. We use it everyday to hook up our laptops to our projectors, or our monitors to our desktops.
When using the cable for computers, five of the 15 pins that are on a 15-pin connector are designated to carry an analog RGBHV signal to the display device. Some display devices also will use a 15-pin monitor cable to input other types of signals as well, and most commonly, the component signal.
Usually it is a projector that will use its monitor input for different multiple signals, due to space restrictions on its input panel. However, it is important to remember that just because a display device has a monitor input, it doesn't necessarily mean that the monitor input can be used for anything other than an analog RGB type signal. That said, you must consult the manual. If you find out that indeed you can input a component signal, all that you will need is a break-out cable. For component video, a break-out cable will have a 15-pin monitor connector at one end, and three RCA type connectors on the other, as shown below.
Keep in mind that monitor cables are length-limited without amplifying the signal. We recommend that you use an amplifier with lengths of 35 feet or longer when using a 15-pin monitor cable with an RGB Type signal.
The world of digital video cables is still a bit confusing. The first thing to remember about all digital cables mentioned here is that any digital cable can be converted to any other type of digital cable with a simple adapter or break-out cable.
All digital cables can carry any type of signal that we've talked about, but are used primarily to carry digital and analog RGBHV computer signals and digital and analog component video signals, depending on the type of cable. As with any cable, buying a high quality cable will ensure that no resolution is lost in transit.
Additionally, there are two important factors to consider if you are running digital signals. They include:
- If you are running cable above a length of 15 feet, you will need an amplifier, which adds additional cost;
- If you are using a digital cable to run an HDTV signal, you must find out if your display source is outputting an HDCP enabled signal. If it is, then make sure your display device can accept an HDCP enabled source. If it cannot, you will not be able to use a digital connection and must use analog component cables instead. Please refer to our HDCP section for more on about this issue.
DVI-I: — A DVI-I cable is only used when your display device can accept either an analog or digital signal through its DVI input. The input is usually clearly marked or is clearly stated in the owner's manual of your display device. If your display has a DVI-I input, you can use the input to show analog component video, as you would with a monitor cable. And, just like with a monitor input, you will need a special cable that has three RCA type connectors on one end and a DVI-I input on the other. A DVI-I input looks like the image shown below.
DVI-D: - DVI-D cables and inputs are digital only, so they are not used to input analog component video, like that from a DVD player. Most newer cable, satellite, and HDTV tuners output pure digital signals, usually through a DVI-D or HDMI connector. Going from a DVI-D output to any other digital input is as easy as figuring out what type of adapter to buy. See the image above for an example of a DVI-D input/output.
M1: - An M1 connector is a type of connector that was first used in 2001. It is a type of DVI connector that also carries a USB signal. This is — and was — very useful in the business world as people with projectors no longer had to carry two cables to connect projectors to laptops, and to use a remote mouse.
M1 connectors come in three varieties: analog only (M1-A), digital only (M1-D) and both (M1-DA). Be very careful to read your owners manual carefully to find out which M1 input you have.
Going from an M1 output to any type of digital input is as easy as ordering a cable with an M1 connector on one end, and a DVI or HDMI, connector on the other. Usually the other end of the cable will split in two, with a USB connector on the other end. (See below).
Most M1 inputs are M1-DA's, enabling you to input any type of signal you want. Inputting an analog component signal would require a cable with three RCA type connectors on one end of the cable and an M1-DA on the other.
HDMI: — HDMI cables are a relatively new type of digital- only cable that was introduced for home theater usage. Since it is used solely for digital video, it's usually used to run a digital component signal only.
There are two differences between DVI-D and HDMI. HDMI end connectors are smaller than DVI connectors, and an HDMI cable carries digital audio as well as video. Obviously this is a great idea for home theater since it frees up a lot of space otherwise taken up by both audio and video cable.
Converting one cable to the other will require some sort of adapter cable because the digital audio line needs to run on a separate cable if going from an HDMI output to DVI-D, and if going from DVI-D to an HDMI input, the digital audio line will have to be merged with the cable or run separately altogether.