Hi,
The Sandbox tool isn’t well-suited for testing the Doppler effect, as it can’t accurately simulate precise movements and velocities. For effective testing of the Doppler effect, using a game engine is preferable, just as DrewKski0 suggested.
I can see this has already been added to our feature request list from our record, and I’ll add you to the list of people interested in it. Thank you for bringing this to our attention!