How can I edit a song from itunes on an ipad?

Garageband can edit songs, and you can get garageband on iPad though I have never used the iPad version:

http://itunes.apple.com/us/app/garageband/id408709785?mt=8

although if you just want to edit sounds (not songs) there is this: http://itunes.apple.com/us/app/pocket-wavepad/id395339564?mt=8

http://www.ipadcreative.com/blog/2011/3/29/a-superb-40-minute-garageband-tutoria l-video.html

http://help.apple.com/garageband/ipad/1.0/index.html

You can trim files in iTunes by adjusting the start and end times.

To delete portions, Audacity would be a better tool.

If you actually want to add audio into a GarageBand song then...

Adding audio sample to GarageBand

Connect the iPad, select it in the left-hand column, open the Apps tab, scroll down to File Sharing, select GarageBand, add files with the button or drag and drop onto the file area. Files should be uncompressed audio in AIFF, WAV, CAF or Apple Loops format at 16bit, 44.1 kHz.

Insert audio sample into song

Open song in GarageBand on iPad, if needed switch to Tracks view or stop if playing, use the loops tool, audio files section, to insert your audio...

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