Analog Video Connections 101

As the technology inside consumer electronics evolves, the connectors used to transfer data between devices is constantly changing and being upgraded as well. A device from less than five years ago won't have any of the high-def connections you see on current electronics. Some of these connections are outdated for HD enthusiasts, but they are still available on most current equipment. A basic understanding of these connectors is essential for anyone setting up a home theater or even connecting a DVD player to a TV.

Analog video is a continuous signal that changes over time, very similar to a sine wave. In an analog interface, the original digital signal is converted to analog, sent over the wire, and then if necessary converted back to digital. Every time the signal is converted, some quality is lost and noise is introduced. This shows up as the pixelated "snow" you see on older televisions with bad reception.

An analog video signal consists of the following components: Luminance, Chrominance, Synchronization and Blanking Pulses. Luminance (Y) or Luma refers to brightness of the image and contains all the black and white information of the picture. Chrominance (C) or Chroma carries the hue and saturation of the picture, which is the color information. Synchronization keeps the timing of the signal and the Blanking Pulses sets the black level.

Here are some of the popular analog video connections available:

Composite Video
Composite Video can be considered the "old" standard for video. A composite video connector consists of only 1 wire but is often seen as a group of 3 wires that includes audio, with RCA Plugs on the end. Usually these wires will be color coded, with the yellow wire carrying the video signal.

Composite video contains luminance, chrominance, synchronization, and blanking pulses together in a single signal; this creates one of the main disadvantages of composite video. Every time the signal is combined and then split back up, the signal gets degraded. This degradation leads to artifacts and noise.

S-Video (Y/C Separated Video)
S-Video (separated video, not super video) sends the luminance and chrominance as two separate signals. This leads to an improvement over composite because televisions display the Y and C signals separately, so there is no need to combine them and then split them back up. Think of it like a black and white picture with a layer of color on top of it. S-Video in consumer devices is limited to 480i, which is standard definition.

Component Video (YPbPr)
Component video gets confused with composite video very frequently. This is partially because of the similarity in names, but also because both cables usually have RCA connectors, a component cable will fit into a composite jack and vice versa. Component video sends the picture as three separate signals (Y, B-Y, R-Y). The Y signal is the same as the luminance signal sent in S-Video, but component takes the color signal one step further by sending it as 2 separate signals. These "color difference" signals represent Blue (Pb) and Red (Pr). Green is derived from the combination of the other three signals to end up with a full RGB signal.

Component video supports progressive scan, which is an improvement over interlaced. Progressive scan displays all the lines of video in order, while an interlaced signal paints the odd numbered lines and then goes back to draw the even numbered lines. Progressive scan becomes more important as screen sizes get bigger and resolution gets higher. This is noted in the i and p you see at the end of screen resolution formats.

The other big advantage of component is the support for higher resolutions such as 480p, 720p, 1080i, and 1080p. Devices that have AACS (Advanced Access Content System) copy protection built into them have crippled their own component video sources by limiting the resolution to 1080i. The belief is that it is easier to duplicate the HD signal if it is being sent over unprotected analog cables.

VGA (Video Graphics Array)
VGA connectors are used more often with computers than televisions, but recently we have been seeing the lines between television sets and computer monitors start to blur. VGA has been the computer standard since it was designed by IBM in 1988, and is only now being phased out by digital video interface (DVI). VGA can display HD video all the way up to 1080p. This can be seen in the Xbox 360 VGA Cable, which is the only way to watch movies with the Xbox HD DVD player in 1080p for people who do not have the newer model that includes an HDMI port.

Do you still use an analog connection for your setup? Which one and what is keeping you from making the switch to digital?

Next week I'll cover digital video connections such as DVI, HDMI, Firewire and even USB.

Resources:
TV Connections
So what is "Component Video" anyway?
Why Y: The Benefits Of Y/C Over Composite Video