Prepar3D Hotfix Re-Introduces Sound Bug

If you have installed hotfix 2, Prepar3D version to be exact, detecting the bug is pretty straightforward. When in flight, change the camera to the exterior fly-by view and listen closely. Each time the fly-by camera resets (the aircraft starts to approach the camera) you'll notice that the engine sound is briefly distorted for about 1 second. What's happening is that the playback rate of engine noise is lowered and then quickly raised. Needless to say this hurts the immersion factor and ruins the doppler effect.


As to the reason why this bug occurred in the first place, it seems Lockheed Martin is working on fixing several age old bugs in the FSX Sound System. Which is nice, but there's always a risk of unwanted side effects... This "doppler bug" first occured in Prepar3D v4.4 and was fixed in v4.5 before re-occuring in v4.5 hotfix 2.


We'll probably add a video later that demonstrates the issue. Watch this space.

the fix

The bug will probably get fixed with a future release or update, but should you want it fixed in the meantime... go to your Prepar3D.cfg file.


[ ! ]

Copy and paste this link to get there fast: "C:\Users\%USERNAME%\AppData\Roaming\Lockheed Martin\Prepar3D v4\"


Open Prepar3D.cfg in a text editor of your choice and search for the section header [SOUND]. Now simply add "time_constant=0" (without quotes) below that header, save the file and you're all done. Try some fly-bys again and you'll immediately notice the difference.

sources and links

  • Original bug reporting thread on Prepar3D v4.4


Born out of passion for aircraft engine noise, SimAcoustics was established in 2019 to cater to the needs of add-on developers for modern flight simulator software such as Flight Simulator X, Prepar3D and X-Plane. In 2020 we added ready made sound packages for end-users to our portfolio.


No matter the scenario, our goal is to immerse the end-user through highly authentic sound environments that push the limits of the respective sound system.


Want to have a listen? Check out our channel on YouTube!