https://bugs.winehq.org/show_bug.cgi?id=56702
--- Comment #2 from ttacwh+fgpjlj0hrlk5k@pokemail.net --- Yes, it's an old now-defunct mmo - Asheron's Call (retail servers are no longer up, but there are emulators and the client can still be downloaded). It's also likely that other older apps/games might use lower sampling rate sounds with directsound.
The game client itself uses a pretty wide variety of sampling rates for its sounds/secondary buffers (8000/11025 mono for the older sounds all the way up to 44100 stereo for the newer), so it is pretty obvious when lower samplerate sounds get incorrectly resampled.
Also, I noticed if you simply double both $approx_bandwidth and $fir_step values (from 0.85/120 to 1.70/240, respectively) and regenerate fir.h with it, that the resulting spectrographs appear more in line with expectations and the resampled audio sounds better as well.
Don't take that as a real fix, however, as I'm not an expert in dsp. Not sure if that is actually the correct thing to do or if there's an actual calculation bug in make_fir (or even mixer.c), so I'm hoping someone who knows this stuff well might chime in :)