No, actually, the .txt file is all you need - TXT files are the ones that AddMusic needs to insert. The SPC doesn't really serve any fundamental purpose other than to be used as a sample for showcasing your song, or for letting others know how the music will sound before they insert it.
But yeah, you will (100% of the time) need to rework the TXT file first. PetiteMM is pretty good for getting the melody to be somewhat close to the correct song, but it's not enough; you also need to assign instruments, optimize the music by adding loops, and make any other tweaks you think you'll need to make the song sound good.
I know that might sound complicated, but don't worry - there's a detailed tutorial on it here
. Look through that for a bit and you'll get it eventually!
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