Confusion Begets Controversy

THX tries to define a listening (or, in the case of HDTVs, viewing) experience, rather than just a set of hardware specs. The very act of doing that makes the company somewhat controversial. On one side are the purists, who suggest that only high end products should be worthy of certification. Anything else – a THX logo on PC speakers, for example, is a sellout.

This is exacerbated by confusion between what THX tries to deliver and what any individual product might include in its feature set. Take A/V receivers: companies will bundle in extra features into THX Ultra2 certified receivers that actually have nothing to do with what the THX certification is meant to deliver. So users may assume those features are available on all products with that certification.

Then there’s confusion between audio and video certification. A good example of this was the recent controversy revolving round the Lexicon BD-30 high end Blu-ray player – which turns out to be a repurposed (and supposedly tweaked) Oppo BDP-83.

THX worked with both Oppo and Lexicon to ensure that the video capabilities met THX standards for video, including linearity of the signal and other factors. Oppo took some of what it learned, and worked that back into the original Oppo product. The Lexicon player was criticized not for just being an Oppo in Lexicon skin, but for not meeting THX audio standards… except that the player wasn’t certified for audio at all, just video.

But the very act of working with Lexicon to certify a product that was simply a repackaged and tweaked Oppo player left some analysts wondering what value THX really brings to the table. If, after that effort, all you need to do is upgrade to the latest Oppo firmware to get those video tweaks, what’s the value of the Lexicon player, other than a fancier external package and a logo? THX trades on its expertise in audio and video, but in the era of the Internet, being a company of high priests with secret sauce is a little more difficult.

All About Linearity

What does it mean when THX certifies an HDTV? There are already standards, like ATSC, for defining the HDTV signal. How the LCD, plasma or other HDTV tech interprets and plays back that signal is where THX comes in.

There are a key set of parameters that any good HDTV needs to hit in order to achieve maximum visual fidelity. Those parameters, however, don’t exist in a vacuum. Take the idea that an ideal panel will offer a gray scale color temperature of D6500. It’s easy to say that – but then you have to also add: D6500 throughout the brightness range. To achieve that linearity at D6500, THX mode dials down maximum brightness. So the tradeoff is a less bright image, which implies better light control in the room, versus a brighter image with a less linear signal.

Then there are more subjective areas, like contrast. Ideally, you do want as much contrast as possible. But having a 10,000:1 contrast ratio doesn’t mean you get great image quality, if the low range is still visibly gray and the high range is ridiculously bright.

When THX works with a panel provider, they specify settings that try to behave linearly – or at least, predictably – throughout the entire range required. You want a high contrast level, but not at the expense of a deep black level. But if hitting the deepest possible black level adversely affects pixel response time, then the HDTV may have to sacrifice a tiny bit of black level so the response time is fast enough.

Then you run into quirky behavior driven by the HDTV company’s need to compete on specsmanship. High refresh rates are a good example of this. You see quite a few HDTVs out today that advertise a “240Hz” or even “480Hz” response time. Those high refresh rates aren’t real – they’re interpolated. HDMI 1.3a and earlier don’t have the bandwidth to push very high refresh rates. Instead, the panel interpolates intermediate video frames to attain a high frame rate. This, in turn, can create artifacts or simply look odd, particularly with content originally shot on film at 24fps.

So when you enable THX mode in an HDTV, one thing that gets disabled is high frame rates, the idea being that film looks like it should.

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  • maxthomas - Monday, June 1, 2020 - link

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