Hi Ralph,
Good eyes to notice that "it don't add up"
Actually the ticks for multiple notes (eg. multiple 16th notes versus a quarter note) won't add up because (as you guessed) there are spaces allowed. Those spaces were actually the result of a lot of research and trial and error, and they're there for a variety of reasons.
First is that if there were no spaces, then some MIDI playback devices would not play properly. (eg. Please
see this post as well as the original post that is linked within that.) That's a purely pragmatic point.
Another reason is that for most instruments at most times, there is a slight space between the played notes to give them some definition. "Legato" playing blurs that definition between notes, but most of the time we don't play legato (unless directed to). Ergo, the "space" between notes sounds more natural for playback. This is a consideration for Notation Composer, when folks are adding in notes using a mouse or the keyboard.
You may have noticed that the "space ticks" aren't the same for different note durations. These numbers are indeed based on measurements of real players playing pieces, and the averages used in the table (getting there in a minute) that is used to set ticks for various note durations. Mark did a lot of research to try and make the software sound like real people without having to have a "humanize" option (though there are other aspects of "humanization" as well.
These spaces (or "slop", if you will), come into play in the reverse case as well, where Notation software (Player, Musician, and Composer) is transcribing a .mid recording (or your playing into Composer, which is the same thing) into readable sheet music. The note duration in the table is an average duration for a given note. However, there is a degree of flexibility (plus/minus), or a "range of durations", that is allowed for a particular "MIDI note on event" (aka "note") to still be a given note. So yes, the "assigned" tick value for a quarter note is 480, but a MIDI note-on event of a range around 480 will be transcribed as a quarter note, too.
Why is this important? You can try out a few other programs that transcribe MIDI-to-notation to see
Most other programs will give you very strict notation - you'll see all sorts of teensy rests (eg. 64th note rests) and double-dotted notes all over the place. Quite the mess for an "everyday musician" (and others) to read and play. Our software tries to eliminate that type of "busyness" and just give you something you can actually sit down with immediately to read and play.
If you want to mess around with the Note Durations table (or need to set one back to default for any reason), you can find it in Notation Composer (with a song open) using Piano Roll/Save and apply note duration adjustments (far right button on palette buttons row)/Edit note durations (first button on left of the tool palette).
A dialog will open that will look like the following:
NoteDurationTable.png
You can mess around with them if you want, or use the table above to reset to "factory standards"
Hope this wasn't too much of an explanation, but since you asked
ttfn,
Sherry