Making Ringtones on iPhone 4
If you’re trying to convert a song or mp3 file in iTunes to a ringtone on your iPhone 4, it’s actually quite easy.
I’m doing this on a PC, I’m sure it’s very similar on a Mac
First select the tune you wish to convert.
Right click and choose Get Info. Then go to the Options tab on this pop-up window (see image).
You will now need to set the length of your ringtone by entering a value in the Stop Time field. Best to choose under a minute both for length and size of the file. Once done press OK.