HDMI Case Studies
Maintaining HDMI Switching and Signal Path Integrity
Joel Silver is the President and founder of the Imaging Science Foundation, Inc., which was incorporated in 1994 to introduce video quality calibration methodology into consumer electronics.
The Job
A home theater installation featuring a $20,000 projection monitor, a $1,000 Blu-ray Disc player, and a $5,000 A/V receiver.
The Problem
The video projector delivered a marvelous picture when connected directly to the Blu-ray player via HDMI, but when the same signal was routed through the AVR, it looked terrible. The two figures below shows a 1080i test signal as seen through a direct connection (Fig. 1) and the same signal after routing through the AVR (Fig. 2). As you can see, the clean lines of black and white have degraded into a series of swirls and rainbow effects.
Fig. 1: Direct connection. (Image cropped to fit page.)
Fig. 2: Signal after routing through the AVR.
The Diagnosis
Unfortunately, many audio manufacturers are still behind the curve when it comes to implementing video in general and 1080p in particular. They may have added some HDMI ports to their receivers, and their products may be nominally HDMI-compliant, but they're still living by the old rules of analog video, and their products are not ready for the tighter tolerances of an all-digital, 1080p environment. The culprit in this case was overscan, a handy technology back in the days when broadcast signals were choppy at the edges, and pictures had to be cropped and resized to compensate. But in today's digital realm, where every pixel is precisely mapped, that same approach can have disastrous results.
The Workaround
The only way to make the picture work was to take the HDMI path away from the AVR, bypassing the video circuits in the audio product and using an external switcher. Not an elegant solution, but a necessary one, and it worked just fine. The tragedy here is that the client paid for video capability in his product and didn't get what he paid for. The dealer had to apply a little creativity – and spend a little more of the customer's money – to get around the problem.
The Takeaway
Always test, never guess when it comes to HDMI switching and signal path integrity. There are good products out there in the AVR category, and products that are troublesome. Your job as an installer is to know which parts of a system can and cannot handle 1080p. Even if you're putting together a system that's not currently wired to a 1080p TV, I can tell you from experience that the TV set will get upgraded, and you don't want to have to replace the entire system when it happens. Make your signal distribution 1080p capable now, so that when the client upgrades, he'll actually get 1080p to his new 1080p set.
The views and opinions expressed herein are those of the author and do
not necessarily represent the views and opinions of HDMI Licensing, LLC,
the HDMI Founders or any of their respective parent organizations or
affiliates.