To get the audio file to iOS GB , add it to your computer's iTunes library.
Transfer
it to the iPad's ITunes.
Then you can import to GB.
You will need
some sort of audio hardware device to connect a mic.
Then you can playback your
song and record your singing.
There are a lot of detailed vids about moving
files to an iOS device, on YouTube.
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G-Dub
Studio G-fx 15inch quad-core i7 Macbook Pro Logic913