To save time, you can just read the bold writing OR the short summary at the end
I saw some reviews of "Viper4Android", it looked good so I installed it on my OnePlus One (CM13 NOT CM13S). The tutorial I followed was in the description of this YouTube video. I flashed the viper4android zip file (which I downloaded from the tutorial video) in TWRP recovery, in the zip file name it said "lolli" meaning lollipop which isn't the android version I use but apparently all I needed to do for it to work on Marshmallow was enabled init.d and create a file named "08setperm" to the init.d directory created when init.d was enabled.
I followed all the steps of the written text tutorial but after I rebooted my phone as the last step, the viper4android app wasn't making any changes, so after some looking around the app and on the internet for ways to make it work, I concluded that I simply couldn't use it on my device.
I began uninstalling it by first uninstalling the drivers in the app itself. Then I undone the changes I made in the "Universal Init.d" App and deleted everything in that app that I could. I uninstalled "Universal Init.d" when this was complete.
I rebooted the phone and tested the viper4android app to make sure it didn't just magically start working and it didn't so I closed it and used Titanium Backup to uninstall it as it was installed as a system app.
After I rebooted my phone once again, to clear the ram of any evidence of viper4android, I noticed that the "AudioFX" app was gone. I had planned on going back to using that app again as an equalizer since viper4android wasn't working.
I flashed a zip I found somewhere on XDA which was the AudioFX app for CM13, upon opening the app, it would remain blank with only the title bar reading "AudioFX". So it basically wasn't functional.
I then tried updating to the latest build (CM13 nightlies) using CyanDelta, I had the latest update downloaded and I then let CyanDelta automatically flash the zip along with romracers v80 xposed framework zip and then clear the cache etc.
After it was completely booted, I noticed the AudioFX app was still missing. I will continue to flash the latest nightly builds until the audiofx app is reinstalled from them.
The point is, viper4android completely removed the audiofx app from my phone and I can't get it back even if I flash the latest nightly build of CM13. Right now I am flashing a nightly build straight from cyanogenmod downloads that hasn't been messed with by CyanDelta as a test.
Thank in advance!