UI: Allow more actions on the selected note
Currently, in note entry mode, SP leaves the most recently added note selected just after it is placed. If you have accidentally given it the wrong pitch (maybe when you lifted your finger, it moved), you can sometimes put your finger back on the selected note, and drag it up and down to give it the intended pitch. This behavior is convenient, because when you can "pick up" the selected note without adding a new one, you can save yourself the hassle of reaching up to the Undo button, to delete the misplaced note.
However, the SP behavior concerning the selected note is not optimal for several reasons explained below. I have gathered multiple suggestions into this one posting because they are all small changes, and are all related to the selected note.
Picking up the selected note again
It is not always easy to pick up the selected note. Often I find that I create another note and advance the timeline when I slightly miss picking up the selected note. Picking up the selected note should be a reliable behavior, because misplacing notes is a common occurrence. Perhaps the "selection pick up region" can be expanded, to make it easier to pick up the selected note with a second finger touch.
Can drag up and down, but not backwards
Sometimes I place a note and get the pitch right, but I miss my target chord (the previous note on the timeline). The note is still selected, so I want to pick it up again, see the normal cross hairs again, and drag the note back until the cross hairs turn red. But dragging backwards is not allowed. A better approach would be to allow users to drag the selected note backwards, so they could fix the misplacement with minimum effort, instead of forcing them to delete the note and start the placement process all over again.
I wonder if one day it might be reasonable one day to implement a pop up window somewhere to the above left of the selected note, whenever a selected note is active. (Kind of like the cut/copy/paste bar that comes up when you select text in most apps.) The pop up bar would contain four arrows to move the selected note up, down, left, or right (or whatever actions were frequently applied to the selected note.) If such a pop up bar was implemented, users would have a very easy way to adjust misplaced notes. They wouldn't ever have to go through the process of breaking their context, reaching up to the undo button (note that undo is WAY faster than going to selection mode, coming back down to select the note, then deleting it) to delete the misplaced note, and reentering the note again, hopefully in the right place.
Changing note length on the selected note
Currently SP will not let you change the note length of the selected note. I sometimes enter the note in the right place, but realize when I lift my finger that the note is the wrong length (common when I'm transcribing complex music). Because it's selected, I am thinking of the "select an object and then apply changes to it" model, so I want to tap the correct note length button, and have SP change the selected note to match. But SP does not allow note length changes on the selected note. This is not optimal. A better approach would be to allow users to tap any length on the toolbar to apply that length to the selected note. If length-changing was allowed (or flipping from note to a rest), users would have a more convenient note entry (and correction) experience. They could change the characteristics of the selected note, instead of deleting the selected note, choosing the right note length, and reentering the note all over again.
Changing sharp/flat/natural symbols on the selected note
Currently SP does not allow you to change the sharp/flat/natural symbols attached to the selected note. Sometimes I get the right note, of the right length, in the right place, only to realize (while the note is still selected) that I forgot to add a sharp/flat/natural sign. I want to just tap the desired sharp symbol to apply it to the selected note, but that operation is not supported. This is not optimal. A better approach would be to let users change the sharpness of the selected note, to save users keystrokes and the effort of placing a note in the right place a second time.
Working with the idea mentioned above, of popping up an "adjustment bar" whenever a note is left selected after entry, buttons to change the sharpness of the note could be on the bar, along with the 4 placement arrows. The pop up bar might look like this: left right up down sharp flat natural plus minus (for changing the length). A good adjustment bar would really improve the user experience of adjusting notes, because users would not lose their mental context (they could stay focused on the note), would not have to undo / select options / replace the note, and would be able to be more productive at their desired task of entering notes.
As you can see, all these suggestions are related to acting on the selected note. It seems to me that most actions on the left toolbar are candidates for adjusting the selected note, including changing note type (note or rest), changing the length (including dotted notes), sharp/flatness, ties (open or close a tie), and triplets.
I think a pop up adjustment bar (or "change bar") for the selected note would be a very efficient convenience for correcting / changing notes, because it would be right there, 1 or 2 inches from the finger that just misplaced the note. With a bar that close, users wouldn't have to reach very far, tap too many buttons, or take too much time to make a fast fix to the selected note, for sure.