How can I add ,let’s say, an octave to an existing melody, without adding a second voice or typing q before writing. You need this very often while writing for piano.
If you are using a MIDI keyboard, you can simply play the octave, but I imagine you are entering notes via the qwerty keyboard, in which case I expect you’ll have to use Q and then probably have to use CTRL-ALT-UP ARROW to transpose the second note up an octave.
I guess what Soundplane asks for is a substitute for what exists in Sibelius. You select a note, type 8 or shift+8 and you get instantly the octave up or the octave down. And it works for every interval and that’s brilliant. I admit I would love to see that too ! 
Daniel wrote back to me about this and said:
"Not at the moment, Claude, but I’m sure this is something we can add at some point.
For now, you can enable the “Lock Durations” button in the note input toolbox, then engage chord input, and work your way through the existing melody, adding the necessary intervals by note name, and hitting Space when you want to move on to the next rhythmic position. It’s not as fast as making a selection of multiple notes and adding them with a single keypress, obviously, but it does remove the need to change note duration at every position."
But add me to the list of those who think this it is a necessary feature.
I saw a live demonstration in NYC last night that included the new transposition dialog in 1.0.10. This includes an option to keep the original notes along with the transposed notes. So to add octaves you would select a passage (multiple staves allowed), transpose by an octave, and retain the original notes!
By the way, the dialog includes all the interval types one could hope for, including diatonic, etc., and a built-in interval calculator, which becomes extremely useful for microtonal transposition!
Me too. Quick octave. So useful in piano pieces.