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It can be, yes. The only way you'd be legally allowed to manipulate or change someone else's MIDI is if they gave you permission to do so.


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If the sheet music you are talking about is classical music, they are in public domain because the copyrights expire some time after composer's death (50-70 years depending on the laws of the country). If they are contemporary works you can't record and distribute them without getting permission. You can rely here for not taking action but if you want to ...


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