The new rain sound effects introduced in 16w04a are not spatialized. Details and a solution are provided below.

Expected behavior

In previous versions of Minecraft, the impression I get is that rain sound effects are generated in the environment surrounding the player. The positions of these sound effects correspond to locations where the rain is actually hitting the ground. The result of this system is a unique, dynamic, and quite impressive rain soundscape in which the player can hear whereabouts the rain is falling.

Observed behavior in 16w04a

The rain sound effects no longer sound like they're positioned in the environment. It sounds like it's raining in the center of my head. The volume is equal in the left and right channels at all times.

To be clear (regarding the actual sound effects themselves): I like the new gentler rain sound effects. The problem is the lack of spatialization on those sound effects.

The cause & the solution

The new rain sound effects are stereo sound files. OpenAL only spatializes mono sound files. You must convert the new rain sound files to mono to solve the problem. I have confirmed that this solution works by creating a resource pack that contains mono versions of the new rain sound effect files.

Related issues

The rain sound effects are not the only sounds in Minecraft that lack spatialization. The cat sound effects (meows, hisses, etc.) also suffer from this problem. I originally noticed this when cats were first introduced into the game but I just accepted it. Now, I have investigated and it turns out that the cat sound effects are also stereo sound files.

Please consider going through all the sound files in the game and converting them to mono. (This obviously doesn't apply to music or any other sounds that are not meant to be positioned in the environment.)

Just for interest's sake: A note about HRTFs

Minecraft uses OpenAL Soft, which is capable of applying head-related transfer functions (HRTF) when rendering stereo audio for headphones. HRTFs can be enabled with a simple config tweak: Create a text file called alsoft.ini inside your %APPDATA% folder and add the line hrtf=true to it. Now, when playing Minecraft with stereo headphones, you can enjoy wonderful 3D audio. You'll be able to perceive sounds coming from behind you, above you, and below you.

The rain (in versions before 16w04a) sounds particularly impressive with HRTFs enabled. It would be a real shame to lose this so please fix the problem I'm reporting here.