FFTF – (not) a cure for FSX blurries (FIBER_FRAME_TIME_FRACTION)

How FIBER_FRAME_TIME_FRACTION can help you with blurries in FSX and why it’s not a good idea to use this tweak. Optimize your HDD first!


FFTF Tweak

Whenever I use FFTF in this article I refer to FIBER_FRAME_TIME_FRACTION in fsx.cfg. It is an optional tweak that you can place in the [Main] section of your fsx.cfg.

FSX tweak / fix guide

Difficulty: hard

Effect on performance: it’s complicated

Good for: users who suffer from stutters (use FFTF lower than 0.3) / I do not recommend it to users who suffer from blurries (optionally – use FFTF higher than 0.3)

For those who need quick answers

  1. FFTF is (in some cases) a cure for blurry textures.
  2. FFTF is a trade off – you get sharper textures at the price of stutters/freezes
  3. Disk optimization is much better solution
  4. If you are above your PC’s capabilities (like I was flying at 820kn with my usual settings) – no tweak or disk optimization will do the magic – you need to optimize the whole FSX (lower the settings)

The problem – blurries in FSX

Many users, especially those who upgraded their FSX with high quality textures like FTX Global or hi-resolution photosceneries observe blurry terrain on descent and during high speed flight at low altitude.

Cause and solution

The main cause of blurry textures in FSX is the time it takes to load the textures. In some situations you can improve it using FFTF tweak. In most cases the problem lies outside your FSX – in your hard drive performance and disk’s queue length.

To properly deal with blurries you should first optimize your HDD:

  • whenever possible – keep your sceneries and textures on separate drive,
  • keep your sceneries and textures on a dedicated partition,
  • keep fragmentation at minimum level (de-fragment often if necessary).

I got rid of blurries with a proper optimization of my hard drives. You may get some results with FFTF tweak – but they come at a price of worsened performance and you may observe stutters and freezes when high values of FFTF are uses.


Let me quote Adam Szofran – FSX developer:

FIBER_FRAME_TIME_FRACTION determines the maximum amount of time per frame that we will run fiber jobs on the primary thread. We measure how long it took to simulate and render and then multiply that time by FIBER_FRAME_TIME_FRACTION to determine how long to run the fibers. For example, if it took 10 milliseconds to simulate and render and FIBER_FRAME_TIME_FRACTION was set to the default value of 0.33, then we would allow the fibers on the primary thread to run for up to 10 * 0.33 = 3.3 milliseconds. For fraction values of 1.0 and 2.0, the time given to fibers would be 10 milliseconds and 20 milliseconds, respectively.


What it means for you – when higher FFTF values are set – FSX will spend more time loading scenery (loading large textures or autogen). That is the theory. Let’s get back to Adam’s quote:

The operation of FIBER_FRAME_TIME_FRACTION on single core machines has not changed since RTM.

On multi-core machines in SP1, we moved many fiber jobs off of the primary thread and onto secondary threads. Since FIBER_FRAME_TIME_FRACTION only affects scheduling of jobs on the primary thread, it will have less of an impact on the performance of Flight Sim on multi-core machines. In fact, we moved so many jobs off of the primary thread that there probably isn’t enough fiber work left to soak up the full time allowed by the default value of 0.33.

Therefore, on multi-core machines, there’s very little reason to tweak the fraction because it really only impacts performance of single core machines.

Please emphasize the pointlessness of tweaking this value on multi-core machines.

Source and full quote

As you can clearly see – there is no point in tweaking FFTF on multicore machines… or is there?

The statement above could have been completely true back in 2007, but since then a lot of “texture-heavy” add-ons appeared and this changes the situation a bit. My test clearly show that when you have ORBXs FTX Global or a high-quality photoscenery (1m/px or better) FFTF may have a visible impact on blurries.

I tested several different situations using extreme values of 0.9 and 0.1. In some of these situations I saw the difference in results.


Default FSX (optimized drive)

  • I observed almost no difference between the default value, and FFTF=0.9 and FFTF=0.1 values in normal flights. That is because there is not enough data to be loaded to make a difference.

FSX + FTX Global + Vector + openLC (unoptimized HDD)

  • no FFTF in fsx.cfg – blurries occur in low level flight at 320-400 knots indicated and during some descents
  • FFTF=0.9 – small improvement in texture sharpness and lots of stutters/freezes
  • FFTF=0.1 – visible blurries

FSX + FTX Global + Vector + openLC (highly optimized HDD)

  • no FFTF in fsx.cfg – small improvement in texture sharpness compared to the same situation with unoptimized drive (very similar to FFTF=0.9 at optimized drive – but without the stutters)
  • FFTF=0.9 – negligible improvement in texture sharpness and lots of stutters/freezes
  • FFTF=0.1 – visible blurries

FFTF in range between 0.2-0.45 (no stutters at this level)

  • I saw no difference in texture sharpness between 0.2 and 0.45.

My Tests


  • CPU: Intel i5 3570k overclocked to 4.2GHz
  • mobo: AsRock Z77 Exptreme 4
  • RAM: 2x4GB: KINGSTON HyperX DDR3 2x4GB 2400MHz
  • GPU: Gigabyte GTX 660TI OC 2048MB GDDR5 192bit
  • HDD:
    SSHD SEAGATE 1TB 3,5″ ST1000DM003 7200 64MB (FSX textures and sceneries – 1st test)
    SSHD SEAGATE 2TB 3,5″ ST2000DX001 7200 64MB (FSX textures and sceneries – final test)
  • second hard drive (HDD): Samsung HD502IJ 500GB 7200 (FSX core files)
  • power supply: Cooler Master GX LITE 700W RS700-ACABL3
  • cpu cooling: 12cm fan + radiator


  • FSX Steam Edition (SmallPartRejectRadius=0 tweak applied)
  • FTX Global
  • FTX Global Vector
  • FTX Global openLC Europe
  • LOD_RADIUS=4.5

Test flight:

  • default F-18 Hornet
  • straight and level – 1500ft AGL
  • clear skies
  • location: Europe

Test situations:

  1. FFTF – default
  2. FFTF=0.9
  3. FFTF=0.1
  4. FFTF – default (textures moved to a new drive)

Flight description

Flight lasted three and half minutes. I flew (using slew mode) with constant speed of 400 KIAS for 1:45 min and than I flew 820KIAS for a minute.

Test result (default FSX)

With default FSX scenery and textures I experienced no blurry textures at 320 knots and almost no blurry textures at 400KIAS. The difference between default value of FFTF and FFTF=0.9 was negligible in terms of blurry textures (there were some stutters).

Test results (unoptimized HDD)

When I compare first three flights I can clearly see that FFTF works!

In each of these flights (400KIAS) I observed changing quality of ground textures – blurry textures appeared from time to time – some were getting sharper as I flew above them, some did not change. Clearly in the second flight (FFTF=0.9) the quality of textures was best! They were getting blurrier slower and they were getting sharper faster. I also observed increased stutters in the second flight (FFTF=0.9). There were micro interruptions, “hangs” or “freezes”. They lasted (as far as I can tell) up to 0.5s. From my observations in other flights at this settings I can say that such freezes can last for 1 or 2 seconds. For me – they ruined the experience.

400KIAS flight with FFTF=0.1 gave me lots of blurries. At times situation improved, but then it was ruined again.

This is kind of important

FSX blurries occur when new textures are loaded. That is why blurries and scenery sharpening seems sinusoidal – when a new texture is being loaded – you see blurries, and then the texture sharpens slowly. At FFTF=0.1 some textures had no time to get sharp before FSX had to load the next textures…

820KIAS flight was a little different – textures were getting blurrier and blurrier with only a slight improvement. (Sinusoidal pattern of blurrying/sharpening was no longer that apparent). After some time autogen disappeared too. When I stopped the flight – textures got sharp and autogen was loaded in next 25-35 seconds.

400KIAS was the max speed I could sustain without degrading texture sharpness. Yes – blurries occured but then some textures where sharp (this is what I called a sinusoidal pattern). Above 400KIAS the situation was getting worse – even if some textures got sharper – they never got 100% sharp. And after some time the level of blurrieness was higher… and then autogen disappeared.

The best result (optimized HDD test)

The most important was my fourth test flight. Before I took-off – I moved all my textures (ORBX, scenery and texture folders) from my main FSX folder to the new drive. It’s a fast (7200rpm) hybrid drive where I created a partition for FSX add-ons.

Without FFTF in my fsx.cfg my experience was very similar to flying earlier with FFTF=0.9, but I observed no stutters! There was a negligible improvement with FFTF=0.9 and optimized HDD – but it was not worth the discomfort of freezes that I experienced. I also tried some flights with FFTF in range of 0.2 and 0.45 (no stutters at this level) but I saw no difference.

Results explained

This is what I saw after 15-20 seconds of flight at 400 knots. In all situations except FFTF=0.1 the terrain textures were sharp.

And this is what happened next:

For default FFTF value and FFTF=0.1 – textures got blurry. Only a little blurrying occurred for FFTF=0.9 and for default FFTF on my optimized hard drive.

Here comes the important part:

You can see disk queue on my unoptimized HDD. Without the queue on the optimized drive – the texture had been almost as sharp as with FFTF=0.9. Actually the terrain is as sharp as for FFTF=0.9 – only the tracks (new texture loaded a moment earlier) are a little blurry.

Here I hit the wall. All images are blurry – FFTF=0.9 and optimized HDD are sharper – but still a little blurry. This is what happens when you get to the limit of your drive’s ability. No tweak will help you. SSD may be an option – but it is not a cure for all blurries – take a look at the previous picture – drive manages just fine – it’s FSX that is lagging on the far right image.

820 knots

And what happens at this speed?

FFTF does not always help. Just as the optimized HDD does not.

But when they have an opportunity – they do.

And after some time it looks like this:


  1. FFTF is (in some cases) a cure for blurry textures.
  2. FFTF is a trade off – you get sharper textures at the price of stutters
  3. Disk optimization is much better solution
  4. If you are above your PC’s capabilities (like I was at 820kn) – no tweak or optimization will do the magic – you need to optimize the whole FSX
FFTF - (not) a cure for FSX blurries (FIBER_FRAME_TIME_FRACTION)
Article Name
FFTF - (not) a cure for FSX blurries (FIBER_FRAME_TIME_FRACTION)
How FIBER_FRAME_TIME_FRACTION can help you with blurries in FSX and why it's not a good idea to use this tweak. Optimize your HDD first!