You may be crazy with finding out the solution to create a ringtone for iPhone 6 from a song or a sound clip from your PC using iTunes in Windows and Mac OS X. The following solution works right on iTunes 12 and should work well on the other iTunes versions.
Quickly create iPhone ringtone in Windows and OS X using iTunes
Step 1: Right mouse on the targeted song > choose “Create AAC Version”.
Step 2: From iTunes, right mouse on the created song in AAC format > select “Get Info” > From “Option” tab, you are able to set the begin and the end of the part of the song that you want to make it to be the ringtone.
Step 3: Right mouse on the song that you have just edited, click on“Create AAC Version”. Then make a right click on the short AAC Song which have just been made, choosing “Show in Finder”.
Step 4: You know get back to iTunes to delete the song in iTunes, but be noticed that you click “Keep File”, do not move the file to the Trash.
Step 5: From the Finder Window opened in step 4, change the file ending from .m4a to .m4r. And then click on Use m4r if you see the warning.
Step 6: Drag and drop the above renamed file into iTunes, this should make it shown in your ringtones.