In my arc s had my mp3 in the music folder, so, the nexus 4, I put my mp3 on the same site, and I've gone crazy looking me how to change the ringtones for mine unsuccessfully.
Now I will explain such as MP3 songs instead of the ringtones that come by default put:
1 – We connect the phone to PC and copy the mp3 ringtones within the folder, or sounds for notifications notifications. Conectáis that mobile by USB to the PC and not the driver you installed windows, get off the driver here and installed manually (from control-panel device manager).
Another way of putting mp3 ringtones folder, It would be to dropbox for example; from dropbox, inside the folder of your mp3, keep your finger on one and get the menu export-save to SD-card ringtones or notifications (as it is).
2 – Restart the nexus 4, 5…
3 – Let's settings-sound-tone phone and are there!!
4 – If we want put a MP3 ringtone to a particular contact it is not one for all, we must go to the contacts application, select one and choose from the menu “set Tone”.
5 – A marvel of application, You need to try Rings Extended, once installed no longer appear until we access the menus we've seen before, but it is super easy and intuitive to use, recommended!!
Someone has gone mad like me to find the solution?
If this has served you help, You can thank me with a donation by Paypal, Thank you!!