When the Sample Rate of the Audio Mixer or device is not 48kHz, the Ladder Filter output is not correct on PIE. It is Silent at 20000Hz, and other frequencies also sound wrong.
1) Open AudioQA in Editor
2) Locate the MSS_Test_LadderFilter asset in the Content Browser and add it to the default level
3) Open the level Blueprint and add a Set Float Parameter node. Connect the Ambient Sound Actor in the level to the Target.
4) Set In Name to: Cutoff Frequency
5) Set the Cutoff Frequency to 20000
6) PIE and validate it works
7) Stop PIE. Open the Project Settings.
8) Select Windows and change the Audio Mixer Sample Rate to 32000
9) PIE again
Sound plays at full volume
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-199324 in the post.