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For most games, start with the simplest limiter that produces consistent frame times: the in-game cap, a driver cap, or RTSS’s ordinary 30 FPS limiter. RTSS Scanline Sync x/2 is a specialist option for fixed-refresh displays, particularly a 60 Hz display, where it targets approximately 30 FPS while attempting to control the tearline with less latency than conventional VSync.
These methods are not interchangeable. A frame limiter controls when frames are produced; VSync controls when they are presented; Scanline Sync targets a position in the display’s scanout; and VRR changes the display’s refresh timing. Also, “new frame-limiting modes” is not a precise product name, so this comparison treats it as the modern alternatives most readers mean: an in-game limiter, a driver-level cap, RTSS’s ordinary limiter, half-refresh VSync, and VRR.
The short verdict
- Use an in-game limiter first if it delivers evenly spaced frames.
- Try a driver cap or RTSS ordinary limiter when the game’s limiter is inconsistent or unavailable.
- Use VRR when the monitor and GPU support it and the display’s VRR range includes your actual frame rate.
- Try Scanline Sync x/2 when you use a fixed-refresh display, have substantial performance headroom, and conventional VSync adds too much latency.
Scanline Sync x/2 does not universally produce 30 FPS. It targets roughly half the active display refresh rate:
x/2 target ≈ display refresh rate ÷ 2| Display refresh | Approximate x/2 target |
|---|---|
| 60 Hz | 30 FPS |
| 120 Hz | 60 FPS |
| 144 Hz | 72 FPS |
| 240 Hz | 120 FPS |
Therefore, x/2 is directly suitable for a 30 FPS target only when the display is running at 60 Hz. On a 120 Hz display, it targets approximately 60 FPS, not 30 FPS. Historical RTSS discussions describe x/2 and additional synchronization-period controls, but the exact behavior depends on the RTSS version and display mode. See the historical RTSS discussion.
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What is actually being compared?
| Method | What it primarily controls | 30 FPS setup | Main advantage | Main limitation |
|---|---|---|---|---|
| In-game limiter | Frame production or presentation inside the game | Set the game to 30 FPS | Simple and often engine-aware | Quality varies by game |
| Driver limiter | External frame-rate cap through the GPU driver | Set the profile to 30 FPS | No additional overlay utility | Behavior varies by API and driver |
| RTSS ordinary limiter | External frame pacing | Set RTSS to 30 FPS | Per-game control and broad compatibility | Adds another utility layer |
| Half-refresh VSync | Presentation synchronized to every second refresh | 30 FPS at 60 Hz | Predictable cadence and no conventional tearing | Can add latency and stutter when a refresh is missed |
| Scanline Sync x/2 | Presentation timing relative to scanout | x/2 at 60 Hz | Potentially low-latency fixed-refresh output | Sensitive to timing, headroom, offsets, and compatibility |
| VRR plus a limiter | Display refresh timing follows frame delivery | Cap within the monitor’s VRR range | Usually smoothest when frame rate varies | Requires suitable VRR support and range |
A nominal 30 FPS cap means one frame every 33.33 milliseconds. It does not, by itself, prove that presentation is smooth. A game can report 30 FPS while delivering uneven intervals or missing refresh opportunities.
How Scanline Sync x/2 works
A fixed-refresh display scans an image from top to bottom, one scanline at a time, followed by a vertical blanking interval. Presenting a new frame at the wrong point can create a visible tearline. Scanline Sync attempts to place presentation at a predictable location in that scanout, often moving the tearline into an area that is difficult to see.
This makes Scanline Sync a timing-sensitive presentation technique rather than merely another 30 FPS cap. The underlying concepts—scanout, scanlines, page flips, and vertical blanking—are described in the Linux DRM/KMS documentation.
The adjacent numeric setting is a scanline offset or positioning value; it is not the refresh-rate divisor. Selecting x/2 is what creates the half-refresh relationship. The offset must generally be tuned for the display and mode rather than copied as a universal number. Community explanations of the RTSS setting distinguish the offset from x/2.
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Scanline Sync versus ordinary limiting
RTSS’s ordinary limiter delays frame production until the target interval is reached. At 30 FPS, that means aiming for approximately 33.33 ms between frames. Scanline Sync instead tries to coordinate presentation with the scanout position. It may provide a compelling fixed-refresh result when timing is stable, but it has a sharper failure boundary.
If the game takes too long to produce a frame, Scanline Sync cannot manufacture the missing time. A missed presentation opportunity can lead to a hitch or a larger-than-expected interval. Community discussions specifically warn that Scanline Sync can stutter heavily when the application misses its timing target. See the Blur Busters discussion of missed targets.
For that reason, a system averaging 30 FPS is not necessarily suitable. The game must deliver frames consistently enough to meet the timing window. GPU headroom is important, but GPU utilization alone is not decisive: a CPU-bound game can stutter at low GPU usage, while a GPU-heavy game may fail when a demanding scene causes a brief spike.
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Frame limiting
A limiter constrains how quickly frames are produced or presented. It does not automatically synchronize those frames with the monitor’s scanout.
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VSync
VSync restricts presentation to display timing and can eliminate ordinary tearing, but conventional queued VSync may increase input latency. Half-refresh VSync can produce 30 FPS on a 60 Hz display by presenting every second refresh. It is a reasonable choice when predictability matters more than minimum latency.
Scanline Sync
Scanline Sync attempts to control presentation timing and tearline position without using conventional VSync behavior. The usual starting configuration for x/2 is to disable in-game VSync, avoid competing limiters, enable x/2, and tune the offset. Some users combine it with other synchronization settings, but that is a different configuration and must be tested separately. Community setup guidance discusses the common VSync-off approach.
VRR
Variable refresh rate allows the monitor to change its refresh timing to follow frame delivery. When the game fluctuates around 30 FPS, VRR is often more forgiving than a fixed-refresh synchronization method—provided 30 FPS is inside the monitor’s supported VRR range or low-framerate compensation works correctly. Scanline Sync and VRR should not be assumed to be additive improvements; enabling VRR changes the timing assumptions and requires its own test.
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At 30 FPS, the ideal frame interval is:
1 ÷ 30 = 33.33 msUneven delivery can instead resemble alternating short and long intervals, such as 16.7 ms followed by 50.0 ms. The average may still appear close to 30 FPS, but motion will judder. Look at a frame-time graph and presentation behavior, not only the headline FPS counter.
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Evaluate:
- frame-time consistency;
- the number and duration of missed refreshes;
- visible tearing or a moving tearline;
- input latency;
- behavior in the heaviest repeatable scene;
- whether the result changes between fullscreen and borderless mode.
A controlled way to compare the methods
Do not begin with several active caps and synchronization systems. Test one path at a time using the same game scene, resolution, graphics settings, display refresh rate, and monitoring overlay.
- Establish the baseline. Set the intended display mode and refresh rate. Disable frame generation while evaluating the base 30 FPS lock. Note whether the game is exclusive fullscreen, borderless, or windowed.
- Test the in-game limiter. Set 30 FPS and record frame-time consistency, latency, tearing, and missed frames. Test the game’s own VSync separately if necessary.
- Test the driver cap. Disable the game cap, set the driver profile to 30 FPS, and leave the rest of the configuration unchanged.
- Test RTSS’s ordinary limiter. Disable the other caps, set RTSS to 30 FPS, and compare the same scene.
- Test Scanline Sync x/2. On a 60 Hz display, enable x/2, initially disable in-game VSync, avoid an ordinary RTSS cap, and begin with a conservative offset. Test both a light scene and the heaviest scene you normally play.
- Test VRR separately. Enable G-SYNC Compatible, FreeSync, or the relevant adaptive-sync mode, cap within the monitor’s supported range, and check whether 30 FPS remains smooth.
Keep a simple record of the result. If one method produces a clean frame-time graph with acceptable latency and no visible tearing, it is the better choice regardless of which tool is theoretically more advanced.
When each method makes sense
Choose a conventional limiter when:
- the game’s own cap is even and reliable;
- you do not have substantial performance headroom;
- the game is borderless-only or behaves poorly with injection tools;
- you want a low-maintenance configuration;
- the display supports VRR and VRR handles the game’s fluctuations well.
Consider Scanline Sync x/2 when:
- the display is fixed-refresh and running at 60 Hz for a 30 FPS target;
- conventional VSync adds objectionable latency;
- the game can stay comfortably within its frame-time budget;
- you are willing to tune the offset per display and game;
- you can verify the result with frame-time data rather than an FPS counter alone.
Prefer half-refresh VSync when:
- tear-free, predictable presentation matters more than minimum latency;
- the system can sustain 30 FPS reliably;
- the game does not cooperate with Scanline Sync or external injection.
Prefer VRR when:
- the monitor’s operating range includes the target;
- the game varies around 30 FPS instead of holding a perfect lock;
- the monitor and driver combination is stable.
Troubleshooting
Tearing remains visible
Confirm the active refresh rate, check that only one synchronization path is active, and tune the Scanline Sync offset gradually. A missed timing target can expose tearing even when the basic configuration is correct. If the display is running at 120 Hz, remember that x/2 is targeting approximately 60 FPS, not 30 FPS.
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Scanline Sync stutters badly
Lower demanding settings, reduce background load, check for CPU main-thread spikes, and test a demanding scene. If the game cannot consistently meet the timing target, switch to a conventional limiter or VRR. Historical community guidance sometimes cites roughly 70% GPU utilization as a useful headroom rule of thumb, but it is not an official universal requirement. The historical discussion explains the headroom concern.
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The result changes in borderless mode
Presentation behavior can differ between exclusive fullscreen, borderless fullscreen, and windowed mode, especially across Windows and RTSS versions. Test the mode you actually use. If Scanline Sync is unreliable, use the in-game, driver, or ordinary RTSS limiter instead.
The game jumps toward 15 FPS
This can indicate missed synchronization opportunities or a configuration targeting the wrong display cadence. Verify the monitor refresh rate, remove competing caps, and compare against a conventional 30 FPS limiter.
Several limiters are active
Disable the in-game cap, driver cap, RTSS ordinary cap, and VSync paths except for the single configuration currently being tested. Stacking them makes it impossible to identify which system is pacing the frame.
Frame generation is enabled
Separate base-render FPS from generated-output FPS. A game rendering a 30 FPS base stream may display generated frames at approximately 60 FPS, so the correct cap depends on whether it applies before or after generation. Evaluate the base lock first, then test frame generation as a separate workflow.
Decision matrix
| Situation | Best starting point |
|---|---|
| 60 Hz fixed-refresh display and reliable 30 FPS performance | In-game or RTSS ordinary 30 FPS cap |
| 60 Hz fixed-refresh display and VSync latency is objectionable | Test Scanline Sync x/2 |
| 120 Hz or higher display with VRR and variable performance | VRR plus a suitable cap |
| GPU frequently reaches 95–100% | Lower settings and use a conventional limiter |
| Borderless-only game | In-game, driver, or ordinary RTSS limiter first |
| Frame-generation workflow | Define whether the cap applies to base or generated frames |
| Latency-sensitive emulator or simulation | Compare ordinary limiting, exact-refresh VSync, and Scanline Sync in the same scene |
Bottom line
Scanline Sync x/2 is not a newer, universally better version of a 30 FPS limiter. On a 60 Hz fixed-refresh display, it can be an excellent specialist solution when the game has enough headroom and conventional VSync feels too slow. Its benefits depend on exact timing, correct refresh-rate assumptions, a tuned offset, and a compatible presentation path.
For everyone else, begin with an in-game limiter, driver cap, RTSS ordinary limiter, or VRR. Choose the method that produces the most consistent frame-time graph with the least visible tearing and acceptable latency. A clean, repeatable 30 FPS presentation matters more than the name of the tool producing it.
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