how to set ring tone downloaded music

Buy ringtones from the iTunes Store

• Open the iTunes Store app.
• Tap More.
• Tap Tones.
• Find a ringtone that you want to buy, then tap the price.
• Choose an option to automatically set the ringtone. Or tap Done to decide later.
• You might need to enter your Apple ID password to complete your purchase.

Use tones and ringtones with your iPhone, iPad, or iPod touch - Apple ...

music is .m4a and ringtones are .m4r and less than 30 seconds.

Music cannot be used. Google how to truncate and convert music to ringtones.