Melodyne is an amazing program and quite user-friendly once you've tried it a few times. The top version can even analyse polyphonic sound eg. Guitar music and this enables you to change wrong notes. You have to make sure the audio file you send to Melodyne is a clean sound without effects or reverb otherwise the analysis will be confused. Vocal harmonies can be corrected or even created. Really enables you to treat wave files more like MIDI in terms of editing. Certainly warrants all the plaudits it has received.
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