Why Does a Game Suddenly Stutter and Flicker When the Frame Rate Falls Below the VRR Range? LFC Low Framerate Compensation, Multiplication Thresholds, and Floor-versus-Cap Trade-offs Explained
重點摘要
When a game's frame rate falls below a display's variable refresh range, the picture can suddenly judder and flicker because the panel cannot follow such a slow rhythm. Low framerate compensation repeats each frame to lift the effective refresh rate back inside the range, but it cannot create new game frames or fix wildly uneven frame delivery.
A game can be running smoothly, and then, without any obvious change in the scene, the picture turns juddery in a single moment, while dark areas seem to shimmer and flicker. A little later, when the frame rate recovers, everything is smooth again. Many players blame the graphics card first, or suspect the monitor is failing. But when the judder and flicker appear only while the frame rate is low, and vanish when the frame rate rises, the more likely explanation sits in the lower boundary of the variable refresh range. This guide explains the mechanism that is supposed to rescue that situation — low framerate compensation, usually shortened to LFC — and, just as importantly, the limits of that rescue. LFC repeats frames to push the effective refresh rate back inside the supported range. It does not create new frames, its multiplication factor switches as the frame rate moves, and when the frame rate is extremely low or wildly uneven, it cannot save the picture. Understanding those three facts keeps the diagnosis on the right road.
Two Symptoms, Not One: Judder and Flicker
The title names two symptoms, and they must be separated before anything else, because they have different causes and different diagnostic directions, even though they often appear together. Judder is about motion: the camera or a moving object advances in steps rather than flowing, as though frames were missing in between. Flicker is about brightness stability: the picture content barely changes, yet dark areas seem to float up and down in brightness. Judder is a frame-rhythm problem; flicker is a low-refresh brightness-stability problem. Treating them as one fault sends the investigation down the wrong road: a fix for rhythm does not fix brightness drift, and a fix for brightness does not fix rhythm.
A third, related effect should be named and set aside: tearing. Tearing is a horizontal misalignment between the upper and lower parts of a picture, and it belongs to the synchronisation discussion in article 155. The judder in this guide is not tearing. If switching variable refresh off turns the dominant symptom into tearing, that change itself is diagnostic evidence, and the diagnostic sequence below uses it.
How Variable Refresh Follows the Frame
A traditional display refreshes on a fixed schedule, whether or not the graphics card has a new frame ready. When the card's delivery rhythm and the display's fixed rhythm drift apart, the result is tearing, or a new frame waiting for the next refresh, which delays what the player sees. Variable refresh changes that relationship: the display no longer holds a fixed schedule, but follows the rhythm at which the card delivers new frames. A frame arrives, the picture refreshes; no frame arrives yet, the display waits a little. As long as the frame rate stays inside the display's supported range, the refresh interval matches the frame interval, motion flows, and tearing is reduced.
The phrase "inside the range" does the heavy lifting. Variable refresh is not unlimited. It has a ceiling and a floor. The ceiling is the fastest rhythm the display can follow; the floor is the slowest rhythm it can wait for. Inside the range, the system works as designed. Outside the range, whether above the ceiling or below the floor, an extra mechanism must step in. Handling the ceiling belongs to article 225. This guide covers only the floor.
Why a Floor Must Exist
Why can a display not simply wait indefinitely for the next frame? The answer sits in the panel drive layer. Each refresh re-establishes the voltage for every pixel, holding it at the brightness the picture requires. If the interval between refreshes stretches too long, holding that voltage and keeping brightness stable becomes unreliable, and the picture tends to drift in brightness, most visibly in dark areas. Every variable refresh display therefore has a longest waiting time built into its design, which translates into a lowest refresh rate: the floor. The floor value differs by model, and this guide deliberately gives no universal number, because panels and drive circuits differ, and so do their floors. What matters is roughly where your own display's floor sits, not a number that claims to apply to every display.
This also explains why low-rate flicker shows up most in dark scenes. Dark pixels sit at low brightness, where small variations in holding voltage produce a proportionally larger visible change, so brightness drift is easier for the eye to catch. The same display, at the same low frame rate, may look acceptable in a bright scene and flicker plainly in a dark one. That content dependence is itself a diagnostic clue.
How LFC Multiplies Frames, and What a Multiplication Threshold Is
Low framerate compensation works in a straightforward way: when the card cannot deliver enough new frames, the system shows each delivered frame more than once. In principle, if the frame rate falls below the floor, showing each frame twice lifts the effective refresh rate to twice the frame rate; if twice is still not enough, showing each frame three times lifts it to three times the frame rate. The multiplier is not fixed. The lower the frame rate, the larger the multiplier needed, and the multiplier must be chosen so that the effective refresh rate ends up both above the floor and below the ceiling. The boundary at which the frame rate crosses from one multiplier to the next is the multiplication threshold.
A threshold is not a number to memorise; it is a behaviour to understand. When the frame rate hovers near a threshold, drifting slightly above and below it, the multiplier keeps switching. One moment the system uses a double, the next a triple, then back to a double. Every switch changes the effective refresh rhythm. That repeated switching is the key to understanding "sudden judder": the average frame rate may look unremarkable, yet the rhythm keeps changing underneath it.
| Frame-rate position | What the display does | What it feels like | Note |
|---|---|---|---|
| Inside the range | Refreshes in step with new frames | Smooth, little tearing | Variable refresh working as designed |
| Just below the floor | LFC repeats frames, multiplier lifts the effective rate | Slightly steppy, brightness mostly stable | Effect is smaller while the multiplier stays steady |
| Hovering near a multiplication threshold | Multiplier switches repeatedly, effective rhythm keeps changing | Clearly juddery, rhythm feels disordered | Average frame rate can look fine while the feel is worst |
| Extremely low frame rate | Multiplied effective rate still low, or switching too frequent | Judder plus flicker together | LFC help is limited, see the boundary section |
| Above the ceiling | Handled by the ceiling mechanism, not by LFC | A different rhythm problem | Article 225, do not confuse with the floor |
Why Multiplier Switching Feels Worse Than a Steady Low Rate
Many players find this puzzling: why does a modest but fluctuating frame rate feel worse than a lower but steady one? The answer is frame-spacing uniformity. Human vision is far more sensitive to uneven spacing between frames than to the average frame count. At a steady low rate, each frame stays on screen for roughly the same time, moving objects advance in regular steps, and the eye reads it as slow but orderly. When the multiplier keeps switching, each frame stays on screen for a varying time, moving objects speed up and stall in turn, and the eye reads it as judder.
Repeating frames carries a price even when the multiplier is steady: each frame stays visible longer, so the steps in motion grow larger. A low frame rate with multiplication will never feel like a genuinely high frame rate, because no new motion information has been created. That point must be stated plainly, or readers will expect LFC to turn a low frame rate into a high one. LFC improves the display's refresh rhythm so the display is not left waiting beyond its floor; it does not make the game deliver more new frames, and the amount of motion information stays the same.
Floor and Ceiling Must Be Thought Together
The ceiling and the floor are not two separate subjects; they are the two edges of one range. The ideal state is a frame rate that sits stably inside the range: not above the ceiling, not below the floor, and not swinging wildly between the two. When a game's load makes the frame rate swing widely, the rate keeps crossing both edges: high moments are handled by the ceiling mechanism, low moments by LFC, and the two mechanisms take turns intervening, which disorders the rhythm further. That is how a frame-rate average that looks acceptable can still feel terrible: the average hides the swings, and the swings are the culprit.
The trade-off guidance follows from that. Chasing the highest peak frame rate matters less than keeping the frame rate stable inside the range. Graphics settings, resolution, and frame-rate limiting are all tools for stabilising the frame rate, not a scoring contest. Limiting the frame rate to a stable level inside the range is a useful temporary diagnostic comparison; a permanent setting must be chosen against your own display's range and your game's load, and this guide gives no universal setting as a standard answer. The detailed choice of limiters belongs to article 225; this guide borrows only the conclusion that both edges must be considered together.
The Diagnostic Sequence, in Order
Run these steps in order. Each step changes exactly one thing, and the pattern of which changes matter is what identifies the cause. Changing several settings at once destroys the evidence.
Step 1: Establish the symptom pattern. Does the judder and flicker appear only while the frame rate is low, and clear when the frame rate recovers? Low-rate-only symptoms point to the floor layer; judder at every frame rate, high or low, points elsewhere first, and should not be forced into the floor explanation.
Step 2: The variable refresh on-off test. With the same scene on screen, try variable refresh on and then off. If switching it off turns tearing into the dominant symptom and clearly changes the character of the judder, the variable refresh range layer is implicated. If switching it off changes nothing at all about the judder, the floor is probably not the story.
Step 3: Observe the boundary. Notice roughly where the change from smooth to juddery happens, in terms of your own display's frame-rate region. A clear transition, below which judder and flicker begin and above which they clear, points to falling below the floor. The transition region differs by model; record your own display's transition rather than comparing it with someone else's numbers.
Step 4: Steady low rate versus fluctuating low rate. At a similarly low frame rate, compare a period when the rate holds steady with a period when it swings up and down. Steadier feels smoother and fluctuating feels clearly worse, which points to multiplier switching disordering the rhythm. If both feel equally juddery, think about the load layer rather than insisting on multiplication.
Step 5: Exclude the load. Lower graphics settings or resolution and try again. If the frame rate recovers and the judder and flicker clear, the culprit was insufficient rendering capacity, and LFC was only masking the presentation layer. If lowering the load changes nothing, continue with the floor layer. This step matters because insufficient load capacity and falling below the floor look alike but demand different responses.
Step 6: The stable-rate comparison (a temporary diagnostic setting). Temporarily limit the frame rate to a stable level inside the range and try again. If the picture smooths out, the combination of fluctuation plus falling below the floor is confirmed as the main cause. If it still judders, do not force the floor explanation; return to the load layer, the game itself, or other layers. This is a temporary diagnostic setting, not a permanent recommendation.
Step 7: Close with the limits of LFC. If the steps above point to an extremely low frame rate, or to frame intervals so uneven that multiplication still leaves a low effective rate or switches constantly, the judder and flicker will persist. That is not a settings mistake; it is the limit of the mechanism. Record the transition region, the steady-versus-fluctuating difference, and the load-test result, and use those notes for any further diagnosis instead of circling through settings again.
Boundary Cases Worth Knowing
First, LFC is not present on every variable refresh display. Support and multiplication behaviour differ by model and implementation, so it must not be written as though switching variable refresh on automatically guarantees low framerate compensation. If a display lacks the mechanism, its behaviour below the floor will differ — it may simply repeat the old frame on a fixed rhythm, or behave in another way — and the diagnosis must start by establishing what your own display actually does.
Second, at an extremely low frame rate, multiplication helps only so far. A larger multiplier means each frame stays visible longer, so motion steps grow larger; and even after multiplication, the effective rate may still sit low enough that brightness stability remains poor. Extremely low plus extremely uneven is the worst combination: switching is frequent, rhythm is disordered, and no setting inside LFC can fully rescue it.
Third, LFC fixes no other layer. Network delay, a game's own hitching, insufficient graphics capacity, and driver configuration problems are all outside LFC's layer. Steps 5 and 6 exist to separate those layers, and no low-rate judder should be blamed on the floor before they have been run.
Fourth, flicker inside the range and flicker below the floor must be kept apart. Flicker inside the range, driven by refresh-rate changes affecting brightness mapping, belongs to article 205, which discusses that mechanism. The flicker in this guide is the below-floor kind: low effective refresh with poor brightness stability. The transition region and the on-off test are the tools that separate the two.
Five Myths, Dismantled
"A frame-rate number that is not low proves the game is smooth." Wrong. Judder depends on frame-spacing uniformity and on multiplier switching, not on the average frame count alone. An average that looks acceptable can hide swings across a multiplication threshold that feel terrible.
"Switching variable refresh on guarantees smoothness." Wrong. Variable refresh works inside its range. Below the floor it depends on low framerate compensation, and that compensation has limits; extremely low or wildly uneven frame rates remain juddery and flickery.
"LFC raises the game's frame rate." Wrong. LFC raises the display's effective refresh rate by repeating frames. The game still delivers the same number of new frames, so the amount of new motion information does not increase, and the result never becomes a genuinely high frame rate.
"Any flicker means the monitor is faulty." Wrong. Brightness drift at low refresh can be a characteristic of the below-floor layer, and the judgement must rest on the on-off test and the transition region, not on the mere presence of flicker. Flicker inside the range is a separate mechanism, covered in article 205, and the two must not be confused.
"Setting the frame-rate ceiling as high as possible is always best." Wrong. Ceiling and floor must be considered together. A frame rate that swings widely and keeps crossing both edges of the range will have both mechanisms intervening in turn, which disorders the rhythm more than a stable rate inside the range would.
When It Is Worth Having the Machine Checked
Most cases end at step 7 of the diagnostic sequence: a confirmed mechanism, a personal setting choice, or a clear statement that LFC has reached its limit. A check is worth considering when the tests point in conflicting directions — for example, judder and flicker persist in every test state, or they appear even when the frame rate stays well inside the range, or the display behaves oddly under load. Those patterns point beyond settings to the graphics card, its cooling, or its configuration, and that is diagnosis work rather than settings work. Published inspection and repair pricing for this kind of work falls within the shop's three published tiers, from HK$400 to HK$2,800, depending on what the diagnosis finds; no figure outside that range should be quoted for this category. Our shop is at Room 1209, Dali Plaza, Shek Mun. The telephone number is 2186 8010 and WhatsApp is 6558 6806. There is no Mong Kok shop, and there is no on-site service; diagnosis is done at the shop. Before bringing anything in, write down the results of steps 1, 3, and 5 — the symptom pattern, the transition region, and the load test — because those three observations narrow the investigation more than any description of the judder alone.
Frequently Asked Questions
Why does the picture suddenly judder and flicker when the frame rate falls below the floor, instead of degrading gradually?
Because falling below the floor is a boundary, not a gradient. Inside the range, the display refreshes in step with new frames; once below the floor, the system must switch to repeating frames to lift the effective rate back inside the range, so the presentation method changes abruptly, and the feel changes abruptly with it. Brightness stability also worsens at the lower effective rate, so flicker appears alongside the judder.
Does LFC make a game smoother in the sense of more new frames?
No. LFC improves the display's refresh rhythm so the display is not left waiting beyond its floor. The game itself still delivers the same number of new frames. If the game is short of rendering capacity and the frame rate itself is very low, LFC can only make the presentation less disordered; it cannot make the game itself smoother.
Why does a steady low frame rate feel less juddery than a fluctuating low frame rate?
Because of multiplier switching. At a steady low rate, the multiplier stays fixed, each frame stays visible for roughly the same time, and motion advances in regular steps, which the eye reads as slow but orderly. At a fluctuating low rate near a multiplication threshold, the multiplier keeps switching, frame visibility times vary, and motion speeds up and stalls in turn, which the eye reads as judder.
Why does LFC still leave judder and flicker at an extremely low frame rate?
Because the mechanism has limits. At an extremely low rate, the multiplied effective rate may still sit low enough that brightness stability remains poor, and if frame intervals are extremely uneven, switching is frequent and rhythm stays disordered. That outcome is not a settings error; it is the boundary of what frame repetition can do, and the remedy lies in stabilising the frame rate and addressing load.
How do I separate flicker inside the range from flicker below the floor?
Use the transition region and the on-off test. Flicker inside the range appears while the frame rate varies inside the range, and belongs to article 205. Flicker below the floor appears once the frame rate crosses the transition region downward, and arrives together with clear rhythm judder. Recording the transition region and the on-off result separates the two.
Will raising the frame-rate ceiling stop the picture falling below the floor?
No. The ceiling governs the top edge of the range; falling below the floor is about the bottom edge. The correct direction is to keep the frame rate stable inside the range: match graphics settings and load so the rate does not swing widely, and use the stable-rate comparison as a diagnostic step. A permanent setting must be chosen against your own display's range and your game's load, not from a universal number.