240 Hz and Beyond

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November 20, 2009 By Geoffrey Morrison

Click the images below for bigger versions:

Figure 1: A standard video camera takes a single still image 60 times each second (60 Hz). Here Norman is moving quickly from the lower left to the upper right. All the movement between the frames is done "unseen" by the camera.

Figure 2: With no motion interpolation, 120 Hz TVs just double the frames. Frame 2 is identical to Frame 1 and so on. Frame 3 and 4 are the same as Frame 2 from the original video.

Figure 3: With mild motion interpolation, the TV creates a frame only slightly different to the original. Here, the created frame (Frame 2) shows Norman about 15 percent toward where he will be in Frame 3 (which is the same as the original Frame 2).

Figure 4: With strong motion interpolation, the created frame (Frame 2) is very different from either original frame, and shows Norman halfway between where he is/was in the original frames.

Figure 5: In some 240 Hz models, the backlight switches on and off, effectively showing each frame twice and creating a sort of faux 240 Hz. Norman's eyes are peeking out of "Frame" 4 for no reason other than it’s just so darn cute.

NO SPECIAL CABLES

I’ve seen a few advertisements for cables that imply you need special HDMI cables for your 120 Hz TV to work. I’ve even been told this by salespeople. In no way is 120 Hz a transmission format. The conversion is being done internally, and every source you have is either 24 or 60 Hz. Any manufacturer or salesperson who says that you need 120 Hz cables for your 120 Hz TV is either lying or… no, they’re just lying.

And for what it’s worth, HDMI cables either work or they don’t. You either get a perfect image, or it breaks up and/or has very noticeable artifacts (as in, it’s not working). If the picture looks fine, it is. It is physically impossible to get a better picture or sound quality with more expensive HDMI cables over short runs.

Over long runs, the impedance of the cable can more easily affect whether you get any signal at all, in which case better made cables will work where poorly made cables won’t. Note the language: “better made” doesn’t necessarily mean “more expensive.”

Check out our podcast on this topic here.

Comments

December 2, 2009 - 3:29pm — Anonymous

I agree with this article and actually learned a couple of new things regarding the processing technique. The only argument I have is against the comment about "more expensive cables". I agree that you don't need special cables in regards to 120Hz certified or higher but you do need cables with certain capabilities, or that have been tested for a certain aspect. I am referring to 1080p, bit color etc. I do work at a big retailer and it does tick me off when sales associates take advantage (some actually don't know better) of customers. Since the boom of LCD HDTVs, I see more HDMI cables with 120Hz certification being sold. But onto my point, if the author of this article is saying that I won't see a visual difference from a $30 HDMI compared to a $100 HDMI when connected to a Pioneer plasma and running off a Pioneer Bluray player, he is sadly mistaken. And that also goes into the audio aspect of surround sound. Might as well say, you don't hear a difference between fiber optic and HDMI. This is just my opinion, take it lightly or heavily. It is open for discussion, and I mean friendly discussion. Again, very well written article on video processing and easily understandable.

December 3, 2009 - 11:33am — geoffm

Sorry, but you seem to have bought into the hype. It isn't possible for there to be a picture quality difference between a $30 HDMI and $100 (for that matter, $30 is WAY too expensive).

With HDMI, you either get the entire signal, and it's perfect, or you don't get a signal/it has artifacts. If it's the latter, the cable is defective and should be returned.

Your analogy between optical and HDMI is a false one, as you're talking about different audio formats (Dolby Digital/DTS vs. Dolby TrueHD/DTS-MA).

Over short runs there will be no difference in picture quality over HDMI. Over long runs, it's a different story, as the quality of the cable (regardless of price) is important to be able to get a signal at all.

I mention all this in the last page of this very article (direct link) and also we talk about why this is the case in this podcast.

November 22, 2009 - 7:52am — Anonymous

Finally...a well written, easily digestable "manual" to the falsehoods of LCD TV tech, regarding their "ability" to render a natural image without overprocessing. Long Live Plasma! (I miss you, Pioneer.)

November 20, 2009 - 3:13pm — Anonymous

what about plasma vs lcd vs led as far as refresh rates are concerned?

November 20, 2009 - 3:37pm — geoffm

First of all, there's no such thing as LED TVs.

Plasmas create a picture in a completely different way than LCDs. They create an image with many pulses of light per second. Increasing refresh rates with LCDs is one of the only ways to combat an inherent flaw with the LCD technology: motion blur. Plasmas don't have motion blur problems, so they don't need different refresh rates.

This is a vast over simplification, but the way to look at it is that LCDs need 240 Hz to have the motion resolution that plasmas inherently have at 60Hz.

November 20, 2009 - 12:26pm — Anonymous

what about local dimming, i.e. LED backlights?

November 20, 2009 - 12:59pm — geoffm

As far as 120 and 240 Hz goes, the type of backlight doesn't matter. If a company is "flashing" or "scanning" the backlight to create a faux 240 Hz, that can be done with LEDs or CCFLs.

You can read about LED backlighting in this feature: LED Lighting: Little Lights, Big Light