This is a keyboard piece from 1699 using the original notation. It was made in Sibelius.
Many thanks,
David
Try deleting the initial C time signature and adding a 3/4 time signature. If that doesn’t work, the quickest way round this is probably to Select All (not using the System Track) and paste into a new flow.
Thanks for rapid response.
But I need both the C and 3/4.
David
Fudge it with an interchangeable time signature at bar 1, followed by a hidden 3/4 time signature at bar 2.
Ooh, nice one, Leo! That’s going to get some use!
It was new to me, too, Ben, but I can’t think of a better way.
Thanks! I’ll try it. I’d better read up on interchangeable time signatures. That’s surely not in Grove! 
D
Sorry, can you be more explicit about the steps to get C3/4, please, I can only achieve one or the other.
D
Like this:
A lot of things there I have never needed to do before! BUT when I try to drag the 4/4+3/4, it doesnt move. I am in write mode.
D
OK. Got it. I need to hold alt down while dragging and the is not /, but ’ ’
Many thanks!
David
You don’t need to drag. Click the time signature at the bottom of the right panel, then release the mouse - the cursor should now be “loaded”. Now click at the start of the bar where you want to place the time signature.
Alternatively, select a note/rest/barline/whatever on the page, then click the time signature button at the bottom of the right panel.
It worked, with one strange consequence: the minims at the beginning of the first bar turned into tied crotchets when I added the 3/4 at the beginning of bar 2 and all my attempts to force duration have failed.
Dear David,
Regarding the attempts with force duration, have you :
Persevere with Force Duration. Just in case you’re missing something:
Well, I’m glad to see Leo has the same workflow I have
I’ve run across this precise notation before, and my solution was slightly different. If forcing durations is your sticking point, this might help.
Is this the only time signature in the document/file? If so, you could always use the symbol editor to edit the Time Signature “3” to appear as “C 3/4” like so:
If you need other time signatures in the same file, you could still use this method and just use a different time signature glyph like “7,” but that would create the same problem you’re dealing with above.
Actually, on second thought, if you did indeed need other time signatures in the same file, you could in fact use 7. Edit the music symbol for 7 in the same way as before, but when entering it in the score, enter it as [3+4]/4. Then just cut the bar off early with a hidden 3/4 as per usual. That will definitely give you the note grouping that you have pictured (though, I dunno if you need this to appear more often and to what effect in those cases, but it will at least work for what you have pictured 
).
Leo, what software do you use to produce your very helpful demonstration?
Giphy Capture. The direct upload function seems to have broken recently, but otherwise it’s pretty good for quick Gifs.
