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Topic: FAQs - Home Theater Related
Joined: Mar 28, 2005
Posts: 13,100
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This is just a short writeup of early FAQs, I'm leaving this open to a few responses with additional questions to be included, but those responses will soon be deleted, and added to the FAQs as warranted.

1. What is the difference between all the different video types? (HDMI, DVI, VGA, RGB, component, s-video, and composite
2. What is a 75-ohm cable?
3. What is the difference between HD DVD, Blu-ray Disc, and DVD?

1. What is the difference between all the different video types? (HDMI, DVI, VGA, RGB, component, s-video, and composite)

Short answer: In terms of quality you generally get best results from digital connections which include HDMI or DVI-D. Then for non-digital connections quality is, best to worst, VGA (RGB), component, s-video, composite.

Long answer:
HDMI is a digital connection that is gaining major popularity and is on almost all HDTV projectors and TVs sold today. It has the ability to include HD audio and HD video which can be transmitted, over a single cable (consisting of many cables inside) to an A/V receiver or a projector directly. It is considered by many to be the best possible connection available today. It includes provisions for copy protection that won't allow digital backups or copies of the audio/video to be made, which has caused some connection hassles, but for the most part, it delivers the best quality audio and video possible today.

DVI is available as a digital connection (DVI-D) an analog and/or digital connection (DVI-I) or an almost never used analog connection (DVI-A) The analog properties available on DVI cables is identical to VGA, so reference that for details. The digital portion is compatible and comparible to HDMI, but DVI does not allow audio to be transferred over the cable. Separate audio must be run from a DVI device to your audio equipment. Quite often DVI connections are found on computers though a few consumer A/V pieces have DVI as well.

VGA(RGB) video is an existing computer analog video standard that has been around for years. It can carry standard and computer video at HD resolutions 100 feet or more when a quality cable is used. While the 15-pin connector (VGA) is most common, there are actually only 9-pins used to carry the actual video information. These 9-pins consist of red, green, blue, horizontal sync, vertical sync, and their corresponding grounds (sync is doubled up for ground). This means that VGA video can be carried over 5 75-ohm cables and be identical to the video inside a single VGA cable. 15-pin VGA ended cables to 5-wire 75-ohm cables can be found easily, but more common for home theater is 15-pin VGA ended cables that break out into 3 75-ohm component cables. Component video is not the same as RGB or RGBHV or VGA. RGB video puts the horizontal/vertical sync information in with the color information. RGB colorspace, even if carried on only three cables, is not the same as component video colorspace.

Component video has become the home A/V analog video standard. It is the minimum connection necessary to deliver HD video to your display. Three 75-ohm cables make up a component video connection colored red, green, and blue. Typically these cables end with RCA type connectors. The cable colors don't represent true color data the way it does in RGB video, but instead represents contrast and luminance data.
More info:

S-video (Y/C) is about the lowest form of direct analog video available. It carries video on two 75-ohm cables and ends typically in a single s-video 4-pin conenctor. One wire carries luminance (Y) and the other wire carries chrominance (C). It is not possible to deliver HDTV at HD resolutions over S-video and should be avoided when HD video is the source.
More info:

Composite video is the lowest form of direct analog video, and is the most common in the world. A single 75-ohm cable carries all the color, sync, chrominance, and luminance data, put together (composite!). Typically the cable ends in a RCA connection. This is for standard defintion TV only and can't be used for HDTV, but it is also the lowest common denominator for display devices so even if you never plan to use composite video, it is nice to have it available in case you hook up a VCR or a camcorder which can't output HDMI or component video.
More info:

2. What is a 75-ohm cable?

A 75-ohm cable is any coaxial cable that is rated with a 75-ohm impedence. These rating for impedence is the same for many different types of cables already in your A/V setup and they are actually interchangable with one another! The black/white cable that the cable company installs for your cable/satellite system is 75-ohm cable. The cables used for composite, s-video, component video, and VGA/RGB video is 75-ohms. These cables are truly interchangable with one another, but often cable adapters are necessary to go from one end type to another. People often believe that because a cable ends with a f-type connector (cable screw on type) that it can't be used for composite video or digital audio. Not only can you use any 75-ohm cable in place of any other 75-ohm cable, you can mix and match them as you please.

ie: You can use a piece of black coax from the cable company to replace the red cable from component video and then you can use a 'specific' composite video cable (yellow ended RCA cable) for to replace the blue cable, and finally a cable listed as 'digital coaxial audio' to replace the green cable. The results will be identical as using a more common red/green/blue component video cable.

NOTE: There are different ratings for 75-ohm cables with the most popular being RG-6 and RG-59. These two types of cables are rated to carry video a certain distnace and have a certain amount of shielding to protect the signal over that distance with RG-6 being more robust. In a short cable run, say under 10 feet, RG-6 and RG-59 will almost always be indistinguishable.

Composite Video (x1)
S-Video (x2)
Component Video (x3)
VGA (x5)
Digital Audio (coaxial) (x1)
Subwoofers (x1)
Left/Right Analog Audio (x2)

3. What is the difference between HD DVD, Blu-ray Disc, and DVD?

It is important to start off with DVD. Everyone knows what a DVD is. But, often people don't understand what is actually on a DVD. The DVD came out about ten years ago and has basically replaced the VCR for movie playback. The video on a DVD maxes out at 720x480 resolution which is still standard defintion TV and stores the data as interlaced data, most often from progressive frames. Most DVD players these days easily reassemble the original progressive scan data and output it over component video. Newer players may include HD upconversion, but this does not change what is actually stored on the disc: 720x480 maximum resoltion.

HD DVD and Blu-ray Disc are new HD disc formats similar to DVD that were introduced about a year ago. This has resulted in a format war similar to VHS/Beta from 25+ years ago. Like Beta/VHS these formats are more similar to each other than they are different. Most notably though is that the information stored on these discs is truly HDTV video most often created from movies and most often stored on the disc at 1920x1080 resolution. This is a 6 fold jump in resolution between DVD and the HD disc formats. The early players are considerably more expensive than DVD and the format war is likely slowing up sales of players due to uncertainty of which side to purchase from (HD DVD or Blu-ray).
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