Music logic is not necessarily logic in the basic sense. It is using, in Minecraft, note blocks to create tunes. The actual logic is simply timing everything finlely and synchronising cords, sometimes to simulate notes that are not available, or ceritain harmonies and dissonences useful in note block music making.
There is a basic rule to Music Making on Minecraft. Keep It Simple! That said, there are all sorts of complicated ways to help organize the sounds,