So you bought a HDMI cable to connect your 4K Apple TV to your 4K TV. You then got 4K HDR movie contents on Apple TV to see how beautiful 4K movies would render on a 4K TV. The problem is that when you set your Apple TV to 4K output you see flickering and signal noises on your TV. What’s going on? Hint: the first suspect is not your 4K Apple TV, not your 4K TV, but your HDMI cable.
Yep, that’s correct. The first suspect should be the HDMI cable you are using.
Now, we cannot help you check whether your cable is actually bad or not, but there are ways to debug the issue easily. We can give you simple debugging tips, like unplugging-replugging your HDMI cable or changing the video output of your Apple TV and check whether flickering disappears. But if this does not fix the problem you might need to replace your cable.
The good news is there’s a way to check whether the cable you bought is authentic or not, i.e. whether it really supports 4K@60Hz signal or not. As you may already know, there are currently two categories of HDMI cables out there with regards to speed they support:
- Standard (or “category 1”) – this kind of HDMI cable support speeds of up to 75Mhz or up to 2.25Gbps. This level of speed enables your cable to transfer HD videos like 720p and 1080i.
- High Speed (or “category 2”) – this kind of HDMI cables support speeds of up to 340Mhz or up to 10.2Gbps. At this speed it’s easy to transfer 1080p, 1080p with Deep Color, and some 4K signals that has low frame rates like 4K@24Hz, 4K@25Hz, and 4K@30Hz video signals.
The problem is that what if you want to render 4K@60Hz? Ah, now you put your finger to the problem. Well, HDMI Org. claims that High Speed HDMI cables are designed to support 4k@60 (18Gbps), however, High Speed HDMI cables in the market are not being tested for this speed. That is why High Speed cables are only guaranteed to support up to 10.2Gbps of speed as noted above.
If you are interested on what’s the technical difference between normal High Speed cables and Premium High Speed cables, I would strongly suggest reading this article by ninshoshiken.com. Non-Japanese reader will not be able to read it, but the quick explanation is that Premium HDMI cables have a better signal integrity than that of the normal High Speed cables. Please see the eye diagram amplitude between the two waveforms.
Premium HDMI Cable Certification Program
To fix this legacy problem, HDMI Org. created the “Premium HDMI Cable Certification Program” which requires cable makers to test their HDMI High Speed cables for “Premium” support. To quote HDMI Org., “the program is designed to give consumers peace-of-mind when purchasing new HDMI cables for their 4K/UltraHD products that may include features such as 4K/60, BT.2020 and HDR.”
So technically there are only two categories of HDMI calbles out there. But effectively, there are three kinds of HDMI cables sold in the market with regards to the speed they support: Standard, High Speed, and “Premium” High Speed.
Now how do we distinguish between “normal” High Speed cables and “Premium” High Speed cables? Easy, Premium High Speed cables come with the following seal of authenticity:
According to HDMI Org. the seal is “special anti-counterfeit label.” To fight counterfeit cables that have inundated the cable market, it seems the solution that the org. chose is this seal that includes QR code and a holographic fingerprint. Cables that have this label can be checked through a “two-level authentication scan” using a mobile phone and a free app created by HDMI LA.
HDMI Premium Cable App
After downloading the app, it will show you how to scan your cable label like the ones shown below:
Now get the package that came with your HDMI cable. If the package has no HDMI Premium seal at all, then it means the cable you bought is either a Standard cable or just a normal High Speed cable or lower. If there is a HDMI Premium label included, then use this label to confirm its authenticity. Open the HDMI Premium Cable app and then scan for the QR code and the hologram fingerprint:
Depending on whether the seal is authentic or not you will get either one of following results:
So there you go. If the cable you are using is unauthenticated, it means two things: one, the cable you are using were not tested for the speed that it claims to support, and two, you should not use it for your multimedia setup since you’ll probably just be frustrated with its performance even if it works from time to time.
Now, does this mean you need to buy only branded cables coming from big brands like Sony and Panasonic? No, not really. The branded cables are too damn expensive. Just visit your local store find a decent cable and scan it for authenticity before buying. Also, you can trust the cables sold at Amazon, just be sure to scan it for authenticity before using. If the result turned out negative, you can always return it and report it to Amazon to help get rid off the bad apples.
HDMI 2.1 and Ultra High Speed Cable
On a very related topic, there will be a new HDMI cable that is being planned and specified at the moment – the Ultra High Speed HDMI Cable or cable that will support HDMI 2.1 maximum speed of up to 48Gbps.
HDMI org has an interesting tidbid about the upcoming Ultra-HS cable:
The Ultra High Speed HDMI Cable supports the 48G bandwidth for uncompressed HDMI 2.1 feature support. The cable also features very low EMI emission and is backwards compatible with earlier versions of the HDMI Specification and can be used with existing HDMI devices.
Anyway, this will be a new topic for discussion later. For now, suffice it to say that the cables you see on the net that are supposed to support HDMI 2.1 speeds are all unverified! Official testing of such cables has not even began yet, so how the hell could these cable claim they support it? Oh well. We’ll definitely write something about this later.