I think I have the same problem as you, the ringtone volume is really low.
Also when the volume's set over 50%, it's crackling really bad (only on ringtone, the music is perfect, I couldn't believe how much bass it's got).
Did anyone manage to fix it?
I'm using v13, I didn't try to revert it yet, because I'm afraid it might mess up the phone if I do it without restoring my backup.
EDIT: I just confirmed, it's not an issue with v12, only v13, which means I'm having a different problem.
EDIT2: Ok, this is what I managed to find out.
I've opened mixer_paths.dll and found the line:
<path name="ringtone-speaker">
and under it
<ctl name="TFA98XX_BYPASS_DSP" value="Off" />
and changed it to "On" (this was set to "On" in v12, in v13 it's "Off").
Now it's much better, but still too quiet, and if I set the volume to last 2 steps, it crackles.
Now, this wouldn't be much of a problem if I set it below the last 2 steps, but the volume of the notifications is now too low.
Is there any developer out there who can help me fix this?