HDMI, like many cutting edge technologies, lives on the hairy edge of functionality. Like THX certification before it, clever marketing and over zealous, under-informed publishing convinced the consumer HDMI was a must have technology, even long before it was of any use to them.

HDMI Football

Chuck Hinton | Hi Fi Insider

December 2008

HDMI Football

Author: Chuck Hinton, McIntosh Tech Support and the Hi Fi Insider

HDMI FootballHDMI, like many cutting edge technologies, lives on the hairy edge of functionality. Like THX certification before it, clever marketing and over zealous, under-informed publishing convinced the consumer HDMI was a must have technology, even long before it was of any use to them.

A/V installers routinely cringe in fear and consternation at HDMI installs, quoting the crusaders in ‘Monty Pythons Holy Grail’ confronting the killer rabbit: “run away!” As such, I thought I would present to you a simple HDMI survival guide.

The general public still seems to be of the opinion that they need HDMI for Hi-Res video when in fact, component video can send the full resolution and color depth that any source can send and that any display can show. However, you do need HDMI for the Hi Res audio codecs available on Blu Ray, so now we are stuck with it.

A/V installers routinely cringe in fear and consternation at HDMI installs, quoting the crusaders in ‘Monty Pythons Holy Grail’ confronting the killer rabbit: “run away!” As such, I thought I would present to you a simple HDMI survival guide.

Cables:
In their rush to cash in on the HDMI craze every manufacturer in the world with a wire cutter and injection molder started making HDMI cables, many with a blatant disregard for the published HDMI specs. HDMI certified cables are great first step. Unfortunately, price is not a good determiner of success w/ HDMI cables, some ‘high end’ cables don’t meet spec in several ways, the most common being the connector is larger than the 21mm maximum width dictated by the HDMI spec. This can cause the connector to hit screw heads above or between HDMI inputs and keep the cable from seating properly. Overly heavy cables can drag themselves out of the jack as well. The little spring connectors in HDMI cables are quite small and can loose good connection after being plugged and unplugged a few times. Invest in an HDMI cable tester, there are even some that came as 2 boxes, one for each end on the cable, so you can test a cable that is already in the wall.

Hot Swapping:
The plug and play aspect on HDMI is predicated on the units talking to each other and auto configuring, the 12 volt line in the HDMI cable is supposed to be off until the units talk and give permission to send, then the 12 volt line is supposed to become live. Unfortunately, some HDMI units do not do this and have the 12 volt hot all the time. The sudden zap of plugging in the hot cable can scramble the unit or mess up the HDCP keys. When connecting HDMI, ALL units must be fully off, (not just in standby) I suggest unplugging your sources, preamp and TV, connecting HDMI cables, then powering the whole system fully connected. Do not plug and unplug HDMI cables with the units ON.

HDCP:
HDCP copy protection is the method by which HDMI devices get permission to talk to each other. HDCP errors can be indicated by an onscreen message to that effect, but not always. An image that comes on, goes off and then back on again is the result of the unit looking for HDCP keys, not finding them, cutting the signal, and then trying to acquire again. A pink image can also be a symptom of HDCP error. The HDCP keys are in a little chip next to the HDMI jack on components, for some reason, HDMI decided this chip should be re-writable, so its contents (the HDCP keys) are subject to corruption. Hot swapping or spikes on the HDMI line can mess up the keys. Unplugging the unit, leaving it off for a few minutes to let the power supply die down and then restoring power will cause the units to re-write the HDCP keys to the flash chip, repairing the data corruption.

Resolution:
The higher res your signal, the less distance you can send it and the more trouble you are likely to have. Video experts tell us de-interlacing should be done as far up the signal chain as possible, so try to send 480i, 720i or 1080i instead of progressive and let the de-interlacing occur at the TV or as far up the path as possible. Sometimes a very high def signal at the first attempt to pass video through a system can cause trouble, I have found that a system that is having trouble communicating can be fixed by starting at 480i, if the sync catches then, step up the resolution one increment at a time and the units will often be able to sync and stay working after that.

Cable Length:
The higher the res, the less distance you can send the signal via HDMI. Try to avoid spec’ing out cable lengths any greater than necessary. HDMI switchers, couplers or connections add resistance, so try to think of each connection as adding about 20 feet to your run. A single 40 foot cable may pass 1080p, where a 6 foot from source to switcher and a 30 foot from switcher to display may not.

Settings:
Many devices can set frame rate of the signal to either 24 frames per second or 60, 24 looks just fine for most applications, so be sure you are not set to 60 in a system that is having trouble. The video format of the signal going down the HDMI cable can often be set to RGB, Component (YCbCr) or PC (SXGA). Try different formats when having trouble, most TVs display both Component and RGB, they each seem to have their own set of artifacts, so just use the one that looks best on the system and causes the least trouble.

Incompatibilities:
It is a sad truth that not all devices from all manufacturers play well together, some preamps don’t like the signal from some cable boxes, some TV’s don’t like the signal from certain Video up-conversion circuits. When having trouble w/ a system, be sure and try a different TV that may be laying around the house (or bring a little monitor on your installs) and check all your other HDMI sources when having trouble with the first one you try.

Calibrate:
Some displays have a different calibration memory for different inputs, so if the TV was all calibrated for component video, it may not be set up correctly for the best picture from HDMI, so be sure and re-calibrate after upgrading the video connection in an existing system.

I imagine the guy who invented HDMI must have nightmares, reminiscent of the Frankenstein movie where a mob of villagers storm his castle with pitchforks and torches, only the villagers are A/V installers. Clad in belogoed polos, armed with cordless screw guns and saws-alls and guided by the flickering illumination of LED flashlights and cell phone screen glow, they seek to rid the world of the mad scientist and the monster he created, HDMI.


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