We've all been there. We're in the heat of working, editing away; we make a snip or cut with either a key command, menu function, or tool, and bam. It pops up. Stopping us dead in our tracks. We're locked out of doing anything else and are confronted with a do-or-die decision that we must make before we can move forward. The entire universe is shrunken down to a simple call to action. Keep, shorten, or split. But, but, but.... what do they each do? 

In the haste of the moment, not wanting to lose the workflow our minds inhabit at that moment, we usually click return and move on. But are we actually making the right choice? Who wants to stop and take the time to think through each of the three potential actions? Well, I do, right now. Let's go through them together, so we are armed with a more educated instinctive response next time it happens. 

First of all, when does this message come up? It happens when splitting a region with underlying MIDI data that crosses over the split point. It only happens with MIDI note data, however. Sustain pedal, continuous controller or pitch bend messages won't trigger this warning. Their parameter values occupy a single position in time. Notes have duration. Control points don’t. We are being asked the fundamental question: what do we want to do with the notes existing on both sides of the split point? 

Split

The answer, of course, depends on the situation. If we choose SPLIT, the notes are chopped at the split point and left intact on both sides of the new region boundaries. However, the notes in the left-most region do not live on beyond the newly created region end. Nor does it live any longer before the start of the region on the right. So, what you see is what you get. You cannot extend the new region borders and expect to see the original note lengths. This applies to note and pre-exisiting controller data. Logic will maintain the last held MIDI CC parameter value since no additional control points are present. 

Shorten

If we choose SHORTEN, the results are somewhat more destructive. And that is not a word often associated with MIDI editing. In fact, shorten is the most destructive of the three possible outcomes. It clips all the MIDI note data to the right of the split point. And it is irretrievable. If you stretch either of the newly created region boundaries, it's gone. This, of course, has its usefulness. It's a great way to clean up sloppy endings of phrases without worrying about underlying notes lingering past the region's end. 

If you have a sustain pedal or other continuous controller messages, it is lost if extending the left region's end. For sustain pedal, if the value is greater than 64, the message is orphaned and the sustain remains enabled. 

The same behaviour happens with other MIDI CC messages. Extending the left region results in the absence of any further CC info. The last value will remain the current value. Dragging the beginning of the right region yields the expected results. Nothing.

Keep

Choosing KEEP looks to be the same as shorten. But it is actually quite different. A region is basically a container that holds MIDI notes (and other MIDI data). Using Keep, the container is separated into two, but the underlying note data is left intact.  This is useful as a kind of safety mechanism. 

If you drag the end of the left region, the integrity of the note data at the split point is maintained. Extending the end of the left region, you will find the full duration of your original notes. Safety comes at a cost, though. If you do not have Clip Length engaged in your Region Inspector, notes will continue to ring on even if the region looks like it ends. 

Since MIDI CC control points don't have any duration, there is really nothing to either split, shorten, or keep. With all of these three actions, there is no hidden control point information beyond the split point. Extending either of the new regions will reveal nothing. 

These are the main takeaways:  MIDI CC data is basically left alone. It remains intact within both of the newly created regions. If you try and extend the end of the left region or the beginning of the right-hand region, all subsequent CC info is gone. This is a good thing. Why would you want orphaned CC data, with no corresponding notes for it to affect?

With note data, the functions pretty much do as advertised. Split cuts the notes in the middle. Their durations are maintained, with the caveat that part lives in the left region, while part lives in the right region. Shorten truncates them at the newly created region boundary. Keep chops the region (the container) but doesn't actually chop the underlying notes. 

Pay attention to sustain pedal messages if you plan on extending the end of the left region. I get so many tech support questions regarding orphaned sustain-off messages that result from these editing actions. If you extend the left-most region to continue working with it, you will need to enter a sustain pedal off message where necessary manually. 

Has your headache gone away? Hopefully, you will remember some of this the next time you are presented with this editing choice.