[Bug 56702] New: Resampler cutoff frequency for upsampling seems too low

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=56702

Bug ID: 56702
           Summary: Resampler cutoff frequency for upsampling seems too
                    low
           Product: Wine
           Version: 9.8
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: dsound
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

When you use wine directsound and mix in a secondary buffer whose sample rate
is below your device sample rate (for example, upsampling 8000/11025 to
44100/48000), the resampled output has a frequency cutoff at around 1/4 of the
secondary buffer's sample rate (1/2 nyquist frequency) instead of where it's
supposed to be - around 1/2 the sample rate (or ~85% of nyquist freq, going by
make_fir).  You can also visually verify this if you view the spectrum of the
resampled output.

This can be very noticeable especially if your input sounds are of a lower
sample rate but still have higher frequencies present.

Other related aspects seem to be working correctly (mmdev opening the device at
requested sample rate, pulseaudio negotiating sample format correctly according
to logs, no other resampling in the chain).

It seems that the fir resampler logic (mixer.c, fir.h, make_fir) hasn't
substantially changed since it was first added over a decade ago, so this seems
less likely to be a regression.

Additionally, I confirmed that the linear resampler from DSound-Fast_Mixer
patch (from wine-staging) does not have this issue - you can force it to always
use the linear resampler by setting HQBuffersMax reg key to 0.

I don't have a test case to upload, but it should be fairly simple to
reproduce.
Tested on wine-devel 9.8 and 9.9 (linux mint 21.3 / ubuntu 22.04)

Thanks!