Lots of players -- Windows Media Player, VLC etc. -- include an equalizer in the settings or options, but system wide equalizers [that can make a difference gaming etc.] are disappearing from apps like the Realtek Audio Mgr. that's installed along with the drivers. I read that this is due to Microsoft having problems with that sort of thing in win10, & asking companies like Realtek to remove those features, but if that's true or not I have no idea.
The most popular solution seems to be "Equalizer APO" -- sourceforge[.]net/projects/equalizerapo/ -- with links to a few equalizer front ends on that page. You use one of those front ends to set the equalizer configuration, i.e. what frequencies to boost or dim, since Equalizer APO is mainly the guts to make it work. It seems to work in win10, but using it with win10 there's a catch...
Equalizer APO comes with a Configuration program to tie it to playback &/or input devices [those you see when you right-click the speaker on the Task Bar & select Playback devices or Recording devices]. When I run the configuration app in 10 & click to save changes, a message window pops up that it couldn't write to a particular registry key. It's a bit of a PITA I'm afraid, but I got it to work by navigating to the key listed in the message window, then loosening up the permissions for that key. The configuration app will want to restart Windows -- don't let it, but run the app again so this time you can save the results [after changing permissions in the registry]. Note that you'll get one of those message windows for each device you try to associate Equalizer APO with, so to save time you might want to make sure and add everything before you restart.
TO set the permissions for the registry keys needed for Equalizer APO in 10, right click the Start Button, select Run, type in regedit, & click OK. Navigate to the key it shows in the configuration app message window. Right click the key, select permissions, & click advanced. At the top of the window you'll see the owner listed as system -- click change next to that. Click Advanced in the window that opens, then click Find Now, which will list all the possible new owners for the registry key. Select one, e.g. Administrators, then click OK. When you get back to the window showing Administrators [or whatever you chose] as the owner, click the box to apply it to everything under that key. Click OK again, and once you're back to the 1st permissions window, select the user or group that you made owner, & check the box for Full Control, once more clicking OK. Repeat as necessary for any other devices. If the changed key ownership bothers you, work backwards once the configuration app makes its changes, unchecking the box for full control, setting the owner back to System.