Connectivity (1 Viewer)

[ChuckA]

I'm a newcomer to the study of Home Theater technology. One of the aspects that I find confusing is CONNECTIVITY. Between standard RG6 coax, S-Video, Component Video, Composite Video, DVI and HDMI...I'm not sure what is a preferable technology, when it is preferable or why. Another issue is interconnectivity. In a system where there are various components (DVD, DVR, VCR, Surround Sound Receiver, TV) are there issues with remaining consistent between the connections from one component to the other.
These are probably very naive and basic questions but I would appreciate it if anyone could point me in the right direction. Thanks!

 

[FeisalK]

quality-wise, for Video
Composite
S-Video
Component
DVI
HDMI

for Digital audio
Coax/Optical
Firewire (also called iLink, IEEE1394)
HDMI

HDMI also carries multichannel audio so for the least number of cables between the components, HDMI is best

 

[Bob McElfresh]

Hi Chuck, Welcome to HTF!


Fesialk gave you the list. Let me explain the "WHY".

Note: all video cables are made with "coax". If you cut any of these video cables, they would look like your CATV coax. Even the SVideo cable is coax - but it is 2 thin coax cables in a single bundle.

Lets just focus on video signal types.

STANDARD VIDEO CONNECTIONS

Composite - This is usually a single RCA cable with yellow markings. The video signal is MIXED with this type of connection. Your television has a circuit called a Comb Filter that converts the composite video to Seperated Video (or SVideo).

This provides a Baseline quality picture.

SVideo - This is a thin cable with a funny 'keyboard' connector on each end. Inside are 2 thin cables that carry a SVideo signal. This signal by-passes the Comb filter in your television so the video image is better. (No un-mixing needed).

This provides a 20% better picture over a composite connection.

Component - This is simply 3 composite video cables in a bundle. Since the video is already separated at the source, this provides the best video quality (assuming you have a good-quality source).

This provides a 25% better picture over composite.

(The 20%/25% improvements came from Home Theater Magazine based on a 50" reference-quality television using a DVD player as a source. This was for STANDARD VIDEO, not progressive or High Def).

COAX CABLES

Mini/RG59/RG6 - There are 3 rough thicknesses of coax cables. It does NOT tell you how good the coax is, or what application it is used for. (It's kind of like saying a "2-door" car vs a "4-door" car.). You can get video cables made with mini coax, RG59 or RG6. In general, the performance goes up as you go from Mini->RG59->RG6, but the cable also becomes thicker and harder to work with.

There is a lot of myth and 'snake oil' information about cables so let me give you a conservitive, technical description.

Think of asphalt. It's on the road in front of your house, and on the freeway. Does this mean you can drive 55 mph in front of your house? No. The same asphalt is used, but it is built differently depending upon the speeds involved.

"What is the frequency?"

Engineers choose a coax cable based on it's technical specs. Different coax is built with different speed (and applications) in mind.

What you need to understand is some gross frequency numbers:

Standard Video (480i) - tops out at about 4 Mhz
Progressive Video (480p) - Tops out at about 12 Mhz
HD Video (720p/1080i) - Tops out at about 35 Mhz

So for HD video, you want a coax that can handle frequencies up to about 120 Mhz. If you run your video through a receiver or switch, you want it to handle frequencies from 90-120 Mzh


"90 Mhz? 120 Mhz? But the max frequency is only 35!!

Here is the problem: people want a single-number to judge things by. So companies say something has "35 Mhz bandwidth" or "100 Mhz Bandwidth".

While the item in question CAN handle 35 Mhz - this is based on a slowly-changing signal. Things work differently if the signals suddenly change. And with video, one pixel can be black and the next one bright-white so the signals change dramatically all the time.

The problems tend to go away if the cable/electronics are designed with a bandwidth of 3 to 4 times the max expected frequency.

Here is a dirty-little secret: Component cables only have to be compatible with the 1940's Standard Video frequency of 4 Mhz to be called "component cables". Try to be aware of this if you are buying cables for a HD system.

DVI and HDMI

These 2 cables carry a DIGITAL signal. Since digital is much, much less sensitive to the cable, these should in-theory provide the best-possible picture.

HOWEVER - the devil is in the details:

• These have NOT proven to provide a better picture than a good pair of analog component cables. Part of the problem is these are fairly new and there are not a lot of HD sources with DVI and HDMI outlets. And the ones that do have output ports (like some cable box's), are only for 'future expansion'.
• Since these are new, most televisions only have 1 input. People are now screaming that they need 3 or more high-def inputs on their television to handle all their devices (Progressive scan DVD players, HD catv box, XBox or PS2 game systems are very common).
• There is also the copy-protection issue. Hollywood is afraid of a digital connection that provides a 'digital quality' master that could be used to create nearly perfect copies that are then sold on the street-corners in Europe and Asia. So these digital connections have anti-copy features that ... dont bring anything to the party.
• Length issue: these digital cables have a length limit. You can run component video cable 50-100 feet, but not the digital cables.

Hope this helps.