Fractal Noise Speeding up after 30 Seconds

[StevenTapia]

Hello All,

I'm using a fractal noise layer as a displacement map to create a fake fire effect on a static fire image. I need this fractal noise layer to animated across 4 minutes. I'm having a problem where the rotation of my fractal noise speeds up after 30 seconds. I've checked the keyframe interpolation and made sure that's its linear, and that doesn't help. I temporarily turned off the rotattion animation to check the other animated parameters and everything moves smoothly. When I animated the rotation parameter again, it speeds up after 30 sedonsd. I have never run into something like this. Can Someone help?

Thank you!

Steven

[OussK]

instead of a keyframe try to use a Time expression on the rotation value

so delete the keyframes and add this expression 

time*1

[StevenTapia]

Thank you ! I'll try that. I forgot to mention that my first set up was with expressions. all of the animated values were driven by epxressions then I opted to animate them with keyframes to see if that fixes the pseed up problme. 

[OussK]

Actually, you get this problem because you animate both the offset and the rotation at the same time, and after one minute the offset value will jump to a bigger number and that affects the rotation value, this is why you start to see this increasing in speed 

[StevenTapia]

Crazy that this effect can't keep a constant speed. I tried your time*1 and it helped tame the speed, but it did'nt give me the result I had when I originally animated the effect. Thanks for the knowledge. 

[JohnColombo]

Hi @StevenTapia,

Thanks for posting about this issue. As @OussK alluded to, the combination of the Offset Turbulence and the Rotation is what is causing the appearance of a speed-up; as the Offset Turbulence moves further from the focus of the Rotation, the fractal noise appears to move faster, as if you were moving a camera from the center of a wheel to the outer edge.

An alternative approach to try would be to set Offset Turbulence to a location off to the left side of your comp, while still animating the Rotation. To add more linear motion, as your original example shows, try animating the Sub Offset inside the Sub Setting group in the same way you were previously animating Offset Turbulence.

Hope this is helpful,

- John, After Effects Engineering Team 

[StevenTapia]

Thank you @JohnColombo ! I'm glad that this coimunity exists. Thanks for the clarification in the issue. I'll that approach. 

[Mylenium]

It might be smarter to simply use different layers with different parameters and then have "invisible" transitions between them. This is a classicv case of trying to do too much in a single sweep and then things wack out because the parameters interact in unexpected ways when the value ranges change.

Mylenium

[StevenTapia]

Thanks @Mylenium ! I tried keeping everytihing clean. I usually create tons of layers and precomps to acchieve things like this, but this time I was trying to keep things tidy, so that I can use this on any future projects. I'll try that approach as well.