Thursday, March 27, 2008

What the heck are HDMI Amplified/Equalized Cables

HDMI "Amplified/Equalized" Cables
Here's one question that initially was a head scratcher. What's an HDMI "Amplified" cable? It is not "snake oil" unless the amplifier or equalizer is using "electro-static-intermagnetic-resonance amplification" or anything having to do with pyramids.
Well first off, there are really two types of "amplified" cables; Repeaters and equalized cables. A repeater recieves the cables signals, (which are actually split up for proper transmission over HDMI cable) re-combines them, and if its function is simply as a repeater, it splits them up again for transmission over HDMI cables again. It does help clean up signals and allows for longer combined cable runs, but that's not really its purpose. An equalizer cable is similar to the equalizers used in Pro Analog gear to correct for high frequency loss over long cable runs. It takes the signal and digitally equalizes the signal to correct for high frequency losses over long HDMI cable runs. The equalization is matched to the cable, so for best results, cables with built-in proprietary equalization will be more capable than adding a seperate booster/equalizer, or a receiving Switcher with built-in equaliztion. The difference between "designed for the cable" (built-in) and external (seperate booster/equalizers or integrated into switchers) varies widely, it can be marginal, or enough to make a large difference in bit errors, depending on the cables and associated equipment.

Note1: An Equalizer should be used at the end of the cable run, or close to it.
Note: There are those that claim that since digital cables just send 1's and 0's that means that if the cable "works" it is perfect. This is a bit off-base. The closer you get to the "digital cliff" where the signal goes out completely, the more bit errors are likely to occur in a complex "system" like the transmitter-cable-receiver system. This results in video artifacts like "sparkles" where various pixels in the display are of random color values. If bit errors are infrequent enough, they may not be noticed, but large amounts will render the video outcome unwatchable.

So do you need one of these things? It depends. How long is your cable run? If it is long, such as for a projector, or in-wall cabling an above fireplace plasma from across the room, it is likely. If it is not so long, such as for a normal receiver or Cable/Satellite/DVD/Blu Ray player to HDTV connection then you don't.
Bad - image with lots of "sparkles"

Good - No "sparkles"

These images are just resized photographs (ok, not very good photos) of actual bit error artifacts caused by long cable runs. The second image is with the addition of a simple external booster/equalizer with the same cables, and an additional cable for the EQ device to the display.

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