Set custom ringtone on iPhone without iTunes quite difficult compare to this way. But using this way you can create or Make custom ringtone for iPhone without iTunes running on iOS 8 or iOS 9. GarageBand is a great default app with all free features best for music enthusiastic. you can tune your voice and add different sound effect with 1000+ different sound tools and music instruments. This app allows you to create Tones on your iPhone and save it in iTunes format, Publish song on App store, and Share it on social media.
From the full song, you can make custom ringtone using iTunes for iPhone.
You can Tune your music on GarageBand app, Then you can record and save it. 
Recording and saving process for all instruments has been same. Learn how to save and set it as a ringtone.
Steps for Make custom ringtone for iPhone without iTunes: iOS
Step 1: Go to GarageBand App from your iPhone and Open it.
Step 2: Choose your instruments, by using that you want to make ringtone.
Note: if you don’t want make ringtone using any instruments then Choose Audio Recorder and record own speech or beautiful music around you.
Step 3: Once your made ringtone, Tap on right corner triangle and Choose > My Songs.
Step 4: Select Tone by Right Select option from top tab.
Step 5: Now tap on saved tone, That’s you want to set as a custom ringtone on iPhone running on iOS 8/ iOS 9.
Step 6: Default name Should be My Song – Serial Number. Tap on saved ringtone.
Step 7: From the top left corner Tap on share icon. and Set as a ringtone.
Next, Give suitable name, and Tap on Export from right top corner.
Then, You can Use sound as a Ringtone or Standard Text Tone.
Now You can check or change Ringtone settings by Go to The Settings > Sounds > RingTone. Enjoy and create more tones by following to repeat above steps for Make custom ringtone for iPhone without iTunes and Using GarageBand.
