Not all audio tracks are created equal, turning off the emulated 'surround sound' may help
Ever fire up a movie (even one you've downloaded) in the Google Play Movies and TV app on your Nexus 9, and noticed the sound was just horribad? That underwater warbly sound likely isn't an issue with your new tablet, or with the movie you just rented or bought — it's probably an incorrect setting.
There's not much we hate more than bad audio around these parts, so lets have a look at how you might be able to fix it.
Not all audio tracks are the same. While most movies or TV shows you stream or download will have what's called a 5.1 audio track (the common name for a type of multi-channel surround sound audio), some do not. We've noticed that videos without a true 5.1 audio track will sound absolutely terrible if you try to fake surround sound via the settings in Google Play Movies and TV on your Nexus 9.
Luckily, the fix is super-easy. Start your movie, and in the player settings (tap the three dots in the upper right to get there) you'll find an entry for "Surround Sound." When the box is checked, it is enabled. When you uncheck it, it's not enabled.
Now we have no idea if this is a specific Nexus 9 issue (we've not seen it elsewhere) or an issue with the Google Play Movies and TV app, or if it is one of those things that could be automated based on the file you're streaming or have downloaded. We just know that this has fixed things here when we were watching a video with a simple stereo track (and sometimes movies that we were streaming in SD versus high-definition). The next time your video sounds like an old Patsy Cline 78 rpm vinyl record, give it a try.