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1.8GHz PIII Desktop, 512MB 300GB Audigy 2
1.6GHz Intel i7 Quad core, Windows 7 Pro (x64), 8GB, 450GB + 2TB HDD, Blu-Ray, Edirol SD-20, M-Audio Fast Track Pro, Sib 6.2
Si me castigare vis, necesse est me intellexisse.
As an example. To create a triplet of quartet notes/crotchets:
1. Create a single note of the desired duration (quarter note)m and click on it to select it.
2. Type ctrl-3 in Windows, or cmnd-3 on a Mac.
3. You should see the triplet header, the original note and 2 quarter rests.
If you want something besides a triplet, at step 2, go to Note Input > Note Input > Triplet and click on the arrow (see screenshot). This will create a variety of tuplets with their default settings.
If you need different ratios, use the Other button.
While on the subject of Triplets, now would be as good a time as any to let you know that Triplets (indeed all Tuplets) do not conform to other notation standards in Sibelius in respect of Cutting, Pasting or Merging any objects within existing tuplets.
Workarounds include:
1. Plug-ins that allow you to reconstruct Tuplets: you will benefit from experimenting with these to see how they overcome manifest shortcomings of Sibelius in respect of Tuplet handling.
2. Edit Filter - to Cut notes from 'inside' tupleted chords requires two actions, the first: Filter for Copying, the second Filter for Deletion. In other words, Cutting from inside Tuplets is broken into two steps, Copy+Delete. If you don't follow those steps, you may end up with goobbledook when you Paste what you thought you had Copied or Cut.
3. You can Paste an object to the first position of a Tuplet without getting the "cannot paste into a tuplet" error, by selecting just the text (not a note) of its numerator, then pasting.
The fact that such workarounds achieve at least some of the desired outcomes tells me it's actually not intrinsically impossible for Sibelius's infrastrucuture to handle Tuplets intuitively, merely that they haven't gotten around (in 11+ years) to addressing this issue yet.
That would be numero uno priority in my wish list for Sibelius 7.03.1