Instructions found at: https://discussions.apple.com/thread/4419068
Slight update 12/01/18:
The convert function required one more step in 3).
Change in the preferences the "import" from MP3 to AAC
Go to Song's and select the song you want to convert
Go to File on the top and choose "Convert" -------------------------------------------------------------------------------- -----
(specify Start & Stop time to 30-seconds long and click OK)
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(when done iTunes will create a Chime)
Change in the preferences the "import" from MP3 to AAC
Go to Song's and select the song you want to convert
Go to File on the top and choose "Convert" (iTunes will automatically point the location of the original mp3 & the newly created m4a files)
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(rename to whatever you like but must change the extension to .m4r)
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(check under "Get Info" – "Kind" : it's still "Apple MPEG-4 Audio")
1st by dragging that newly changed m4r(original) file to somewhere out of that same default folder it was created by iTunes...
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{ this is where most confusions occur, take note here, it gets rather complicated }
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(u can stop it immediately...) this is just to let iTunes automatically convert that m4r(ori) file into a new duplicate and places it inside the initial default folder where the original mp3 file is kept.
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//to get to that "TONES" Folder : First Locate your iTunes default music folder
usually in your Default "MUSIC" folder --> Navigate to "iTunes Media"
Navigate to "Tones".
Keep this window open to make the transfer manually.
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1) Select a favorite song in iTunes to be made into Ringtone.
2) Get Info on that song and make any 0:30 seconds portion of that song.
3) Right-click or Ctrl-Click again on same song and select "Create AAC Version"
4) to locate the created m4a file easily, Ctrl-Click again on same song and select "Show in Finder"
5) change the m4a file to m4r as suggested...
6) At this point, the m4r(original) file isn't a "Ringtone" file yet... which we'll need to change now)
7) Once it's outside of that folder, Double Click the m4r(original) file and iTunes will play
8) Locate that duplicate m4r(new & true) file, in the same mp3 folder and now DUPLICATE-Drag (press Option while dragging to get the "+" sign) it to the "TONES" folder in your default apple folder structure. (check that under Get Info, your new m4r File's "Kind" should be "Ringtone")
9) Once your duplicate is inside the "Tones" folder, double-click on that duplicate m4r(true) file and let iTunes play, it should automatically place that bloodycomplicated file into the "Ringtone" sidebar List in iTunes program (check program to see)
10) There you go. Now you can Sync / Delete / Add the whole Ringtone contents to your iPhone as you wish. //Don't forget to set SYNC on the iphone to iTunes under "Tones" tab in your iTunes - iPhone screen... and click SYNC button & wait for the magic.
( Finally you can check inside your iPhone "Sounds" settings and hopefully if all steps done correctly, the bloodycomplicatedringtone selection will be there. Enjoy!