Backwards Doppler effect?

New player to SH4. Installed the TMO mod to get me started off on the right foot. I ended up customizing the TMO install to restore the stock loading screens and command bar UI. Just personal preference, although I do miss the buttons that give you the range on your current fuel (great for knowing when to head home) and the current weather from the bridge .

I noticed one thing in the game though. It seems to me like the doppler effect on the aircraft sounds is reversed? The airplanes have a low and deep sounding throttle when they approach and then as they pass the sound gets higher as if he's throttling up to get away. I would think that this should be backwards as the airplane approaching the viewer will have a higher frequency sound as its closing rate is added to the sound waves. Then when the plane passes the plane's speed is subtracted and the sound should get lower.

Anyone else notice this? I don't know how the sound is handled in the game, if some sound files need to be switched around, or if some config parameters can be adjusted to fix the doppler effect?

I did a quick search on this but did not seem to find any mentions of a mod involving a doppler fix.

Norman