Notable unlisted changes in the #13 update
A lot of people have been noticing significant changes to PUBG's audio, specifically the way gunshots sound. It turns out that Bluehole finally shipped a partial fix for the longstanding issues with directional sound, which just happens to be unlisted on the official patch notes.
Since day one, certain sounds in PUBG have suffered from broken panning behavior, adversely affecting players' ability to localize important game sounds, particularly gunshots. This defect has been written about in detail by yours truly in this reddit post and this bug report. The gist is that prior to this patch, certain "loud sounds" had no front-back and up-down differentiation, were subject to 90-degree zones of ambiguity directly to the player's left and right, and exhibited erroneous panning behavior relating to the height of these sounds relative to the player.
These defects culminated in a system so broken that panning errors of 90 degrees were frequently observed. If an enemy was positioned directly above or below the player, the player would hear that enemy's gunshots coming from their direct left or right. Smaller errors were more common, and in order to know from exactly which direction a gunshot was coming, players would have to turn and face the source of the gunshot.
Along with gunshots, other loud sounds like breaking glass, explosions, and vehicle engines were (and still are, unfortunately) subject to these issues. Many quieter sounds, like footsteps and car fires, were and are not subject to these defects, and for a long time have had full 3D localization via HRTF.
What this newest patch has done is enable for gunshots the same processing done on footsteps, so that now gunshots are also localized correctly in full 3D. No longer is it necessary to turn and face gunshots to discern their exact direction. Unfortunately, other types of loud sounds like explosions, breaking glass, and vehicle engines still appear to be affected by the above defects.
For your listening pleasure, here are some before & after comparisons for gunshots:
Full rotation while gun fires (before, after): Notice how the gunshot not longer gets "stuck" in full-left and full-right pannings, and is now panned continuously for the entire rotation. The direction of rotation is also now clearly evident thanks for front-back differentiation.
Looking up and down while gun fires (before, after): Notice how panning no longer errors out to full-left and full-right as the height of the gunshot source relative to the camera becomes more extreme.
As with any significant change to a gameplay critical system, it will take players a little while to understand the change and become acclimated to it before being able to properly evaluate it. This is definitely not an instance of fixing what's not broken; directional audio was clearly and demonstrably broken in ways which sometimes had catastrophic affect on gameplay. I suspect this change will follow the same trajectory as the introduction of HRTF to CSGO, where players vocally resisted the change but eventually warmed up to it over time and as Valve refined the system, to the point where it's now widely understood that not using it puts players at a disadvantage. Chalk it up to growing pains, but this development is definitely a step in the right direction with respect to directional audio in PUBG.
Clearly, there's still some work Bluehole has to do to further refine their audio system. Applying these new effects to gunshots has negatively impacted their timbre, making them sound tinny or hollow. Bluehole should also strive to fix localization for all gameplay critical sounds, just like they have done for gunshots with this patch.
Edit (Fri May 18 2018 09:05:51 GMT-0700): Many are asking if it's still a good idea to use surround virtualization. The compromise at the crux of the matter was that enabling surround virtualization would make loud sounds like gunshots, explosions, and cars easier to localize at the expense of quiet sounds like footsteps. With the sound changes in this newest update, gunshots are now a class of sound which is localizable like footsteps have been. I feel this obviates the need for virtualized surround.
Also, I don't work for Bluehole; I do not represent them in any way.
Edit (Fri May 18 2018 10:32:04 GMT-0700): To people running PUBG through Voicemeeter and noticing dead zones, make sure your speaker configuration for Voicemeeter's virtual playback device is set to stereo. You can find this option in Windows' Sound control panel. If for any reason you insist on keeping Voicemeeter's virtual playback device in a surround sound configuration, but ultimately play with headphones, you can do this but you need to ensure that mixdown is being performed correctly or else you'll end up with dead zones. If Voicemeeter itself is to perform that mixdown, the correct option is MIX down B (MIX down A has phasing issues which result in dead zones between the rear and surround channels). The MIX down B option is only available in Voicemeeter Banana, so you'll have to upgrade if you run regular Voicemeeter.