Howdy David,

Tracks are indeed the same thing as staves, but we changed to the term "Staff" because most musicians understand "staff" readily, but "track" is not as notation-oriented.

For most MIDI players, the channel assignment won't matter, but for some sound libraries (such as Garritan Personal Orchestra) it will matter.

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On downloaded MIDI files, Channel 1 often contains no music - it's just blank. Why is that?
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I think you may mean "Track/staff 1". I see that a lot, as well, and I think it's because often folks will use that track to keep information about the file, such as the file name, the author, and other attributes about the file.

I'm not sure about the history of the convention of putting the melody in the 4th staff, except to say that I've noticed that as well. Maybe someone else can enlighten us both here

ttfn,
Sherry