TCL 50s423 4K TV review: input lag, deinterlacing and upscaling using the piLagTesterPRO
TCL 50s423 review: input lag, deinterlacing and upscaling using the piLagTesterPRO
This 4k TV from 2021 is a disappointing downgrade from other TCL TVs, with variable input lag, but good upscaling.
Image quality
Good upscaling is critical for retro gaming. Ideally, all pixels should appear equally sharp and bright (no aliasing), and angled lines should appear smooth, with no jagged, irregular steps. Also important is that the display shows most or all of the pixels it is sent. Often, this is not the case, with some number of pixels cropped from the bottom or top edges. Shockingly, these tests are relevant for modern gaming as well, because even at their native resolution many TVs have aliasing and cropping.
I attempted to adjust the set to minimize cropping and aliasing.
The set has no options to adjust cropping/scaling. At least not without the remote. 480i/p is displayed stretched to 16:9.
| resolution | aliasing | cropping (side, top) |
| 480p/i | mild | zero |
| 720p | mild | zero |
| 960p | zero | zero |
| 1080p | zero | zero |
| 2160x3840 | zero | zero |
| 2160x4096 | zero | crops rightmost pixels off (bug?) |
480i/p was disappointing given all the native pixels they had to work with. There was a lot of blur, though at least little-to-no aliasing. It doesn't seem like they bothered to make a 480p/i upscaling engine specific to 4k, and thus what could be sharp isn't; it's about as good as a 1080p set would do, though.
All other resolutions upscaled nicely, including 960p. 4k in 2160x4096 exhibited an odd effect where it just discarded the extra pixels beyond 3840, which is poor way to crop down x4096, but of course why would you feed this set a full 4k image when the true resolution is 2160x3840?
The display has 3 HDM inputs and one component input. I only tested HDMI.
Input Lag
I used a piLagTesterPRO to measure input lag. This device sends a frame of video over HDMI and measures how long it takes to display it. Complicating things significantly, this is yet another display that does not actually sync refresh to the input signal - instead it fills its own internal frame buffer from the video input and then draws that with a fixed additional delay that is randomly determined each time you turn on the set or switch inputs. Take one example, input lag at the top of the screen can vary from 37ms to 53ms, outside game mode (this problem occurs in game mode too). What you get seems to be entirely up to chance.
I've elected to report the average lag values here, since that seems fairest, but there's no right answer; for more discussion of this issue see the above link. It's worth noting however, that this kind of changing lag is the hardest for your brain/hands to adapt to. I'd much rather have an extra 16ms of fixed lag added to the display than one like this where sometimes the extra lag is 0, and sometimes it's 16ms. Note that it's not unusual to see this behavior outside of game mode in many TVs, but most TVs don't have it *in* game mode. Sadly, this one does.
There's an additional complication as well: sometimes it doesn't turn on game mode until the TV or input device has been fully power cycled. RTINGs has observed this behavior as well, using a much older firmware than tested here, so this bug is likely permanent, and definitely yucky. You need to test these things, TCL!
This TV reports that it supports 24hz; but it doesn't actually change the redraw rate, it just selectively duplicates frames to simulate 24hz using 60hz. It's maximum refresh rate for TV modes is 60hz; if you switch it to computer modes it can accept a 75hz signal at sub-native resolutions. This does not improve lag, however, as the TV continues to draw at 60hz, and just drops all the extra frames.
Input Lag Test Results
I report two kinds of values. 1st response measures how long it takes for the TV to start responding on average (I use a 5% change in display brightness). This overly optimistic value doesn't tell how long it takes to see anything useful, but matches what other reviewers call input lag. full response is a more realistic measure of lag, and requires the display to reach 80% of full brightness. This combines both input lag and response time, and is closer to what you would actually experience in a game.
| Screen: | top | bottom | |||
| Resolution | 1st resp. minimum | 1st (average) | full response | 1st response | full response |
| 480i | 39 | 47.0 | 60.0 | 62.0 | 75.0 |
| 480p | 6 | 14.0 | 27.0 | 29.0 | 42.0 |
| 720p | 6 | 14.0 | 27.0 | 29.0 | 42.0 |
| 1080p | 6 | 14.0 | 27.0 | 29.0 | 42.0 |
| 960p | 6 | 14.0 | 27.0 | 29.0 | 42.0 |
| 2160p | 6 | 14.0 | 27.0 | 29.0 | 42.0 |
In most modes this TV can have a 1st response as early as 6ms. But because input lag varies by up to 16ms each time you turn on an input, the average lag is actually 14ms. From hereon I will discuss averages only.
Once it starts drawing at the top of the screen, it takes about 15ms to get to the bottom. And once it starts drawing it takes about 13ms to reach nearly full brightness (ie the response time). Thus in total it takes an average of 42ms to finish drawing the screen, which is a long time.
The only interestingly different result is 480i, which is about 33ms slower than all other progressive modes. That is to say, deinterlacing takes about 2 frames. The results look very good, ideal for text heavy slow paced games (RPGs). But the total is so long that retro action games would be a disaster on this set, unless you use a retro-specific fast deinterlacer, like the OSSC. Indeed, this set looks very good at 960p and would be well suited to the OSSC, if you don't mind the flicker caused by the BOB method.
Results compared to other displays
To allow quick comparison between many displays I've summarized the results
across all the displays I've personally tested with the piLagTester Pro. Min
lag is the average time to the first response, measured where the screen starts
drawing (typically, the top); real lag is the time to the full response,
measured where drawing finishes (usually the screen bottom), i.e. input lag +
scan out + response time. Numbers in red denote average values that can vary by
up to 8ms between power cycles.
This list is sorted by real lag for each display's native resolution and max
refresh rate (usually 1080p60 but some sets are 720p60, and other monitors
support > 60hz).
This set doesn't do as well as the other TCL sets I tested, mostly because of the variable lag, but also the slower response time. It's about average for a good 2010 TV, which isn't saying a lot for a modern 4k TV! Meanwhile the two other TCL TVs I tested (TCL 49s403, TCL 40S325) do better, nearly at the top of the list with no variable lag in game mode, and faster response time. Hopefully it's not a regression in the firmware (I tested 4209-30, the latest as of Sept 2021).
Conclusion
I might be overly hard on this set, since I'm mostly disappointed in the big regression relative to the other TCL TVs I've tested. It's still above average on my (at this point quite lengthy) list. But many of those TVs are quite old, one would have hoped for more progress.
Other models
I tested the 50S423 HDTV, which is the 50" version.
According to RTINGs this TV comes in many sizes, but also in several model names that differ in essentially nothing (such as the store it's sold in). IDK, I have no interest in looking up all these variants to see if they really are the same even in terms of specs (and certainly I'm not going test them in person)... But here's their list for cross reference:
43S425 43S423 43S421 49S425 50S425 50S423 55S425 55S423 55S421 65S425 65S423 65S421 75S425 75S423
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