Originally posted 7/20/2017
Even with 48Gbps around the corner, it’s 4K@60Hz that continues to headline the HDMI news. That’s because the 4K@60Hz that many thought we had four years ago is just now surfacing in products integrators are deploying. With that comes interoperability issues, producing a sudden increase for 4K@60Hz support throughout the industry. These requests come from retailers, CEDIA integrators, OEM companies, electronics manufacturers and more.
When Rev 2.0 was introduced, its prime objective was to provide a 4K@60Hz format for consumer video. However, as many know by now, the 4K@60Hz first introduced really did not challenge or use the specified bandwidth expansion to support high quality 4K under Rev 2.0.
For almost two years, this important information was mostly overlooked (or kept very low profile, depending on how you view it) by the industry. It was not until HDR took center stage that brought to light the need for the bandwidth expansion. This paved the way for 4K@60Hz to take advantage of deep color and improved color subsampling.
However, now with real products hitting the markets with real high-bandwidth 18Gbps material, the challenges to reproduce Rev 2.0’s true 4K purpose are revealing themselves.
The reasons are multifaceted. When a system makes the jump to 18Gbps a few things happen on the fly within milliseconds. It’s these changes that are causing most of the issues being reported. We see this in our laboratory. We have all kinds of products that simply don’t work. So, why are there so many interoperability issues?
Well, even many of the test instruments being used throughout the industry have these anomalies. At DPL we have a variety of products for testing, including color bar generators and analyzers that integrators use in field applications. All it takes are just slight anomalies to produce different test results.
We had a popular 4K Blu-ray player come in for evaluation and found that this machine performed admirably with just about every product we threw at it — impressive! As more transmission products came in for testing, this continued to be the case. What was interesting, though, was that a fair amount of the products did not pass test and measurement requirements. Some were off the charts; some functioned using color bar generators while others did not. But all seemed to work with this one player.
To substantiate these findings, we decided to build a test fixture that would allow us to “look under the hood” of this component while it was playing 4K content for a new Sony 4K@60Hz display. Having the right test equipment allows an operator to force the display to produce a true 4K@60Hz 18Gbps image, proving the display can in fact reproduce this.
The test fixture was designed to be invisible to the system it was monitoring. After building the fixture and testing its specific attributes to produce these numbers, the real test awaited. As the Blu-ray player was playing back 4K@60Hz content, we introduced our non-volatile HDMI “Video Snooper.” With this fixture in place, we can view the digital video data being transmitted from the player to the display without the system knowing we are intruding. These tests are done with Eye Patterns, a standard test function with all high-speed data test practices, and they were truly an eye opener. The diagrams can easily be used to verify the data rate being received. The Blu-ray’s data rate to the Sony display was 2.97Gbps.
Remember, we are measuring just one channel of the three, so the aggregate of the channels compute to 8.91Gbps. If this was a true 4K@60Hz 18Gbps transmission the signal channel data rate would be 5.97Gbps. The player was sending low data content. But here’s the rub: When the player is initially turned on and its splash screen appears, it produces the 5.97Gbps that we were expecting. So apparently the “4K@60Hz Disc” that was specifically designated for this type of viewing was unable to support the high-bandwidth 18Gbps product!
Some test analyzers can evaluate these features, but in this case, the test instrument was not getting the entire story. This will cause other interoperability issues as more 18Gbps products hit the streets. We need better transparency among these products.
More on HDMI 2.1 and 4K@60 from Jeff Boccaccio
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