The Sibelius Sounds library which ships with Sibelius 7 and later does not have support for reduced player configurations such as a2, a3, a4 etc., but if you are a NotePerformer user, you are in luck.
NotePerformer 3 installs a plugin in Sibelius called “NotePerformer a2, a3 … MIDI message” which appears in the Plug-ins page of the home tab.
This plugin adds a MIDI controller message to a beat, or the start of a selected region for playback when using NotePerformer.
In other words, you can apply this plugin to add hidden MIDI controller info at the same location as the “a2” text, so that NotePerformer produces correct playback of a2 etc.
You can use the plugin to add this MIDI Controller data each time, or you can also add this controller info directly in your score either manually or automatically with NotePerformer.
The plugin uses MIDI controller 104.
You can manually type the MIDI data info into your chart where you want them, as part of the “a2” or “a3″text, but hidden.
The tilde character (~) prefix is required for midi controllers in Sibelius and will also hide the subsequent controller text. Syntax is “C” for Controller, the number “104” for the Controller Number, comma, then add the Controller Value of 2, 3, or 4, etc for the number of players.
tutti ~C104, 0
(this resets to the full ensemble sound from a smaller number of players like a2 or a3)
a2 ~C104, 2
a3 ~C104, 3
a4 ~C104, 4
a5 ~C104, 5
a6 ~C104, 6
(same syntax all the way to a8)
You don’t have to type out the strings each time. You could create all of these techniques as Word Menu items so that you don’t have to type them out each time., using the same process as shown for “tutti” below.
Even better, you can define a2, a3, a4 etc. and tutti entries in Sibelius’ Playback Dictionary so they will be automatically applied with the text.
Create a new a2 entry in the Staff Text section of the Playback Dictionary, and then use the Control Change Effect to set the playback. Use MIDI controller 104 with a Controller value of 2 for “a2”.
Repeat for the various numbers of players; a3, a4, a5 etc and change the corresponding Controller value to equal the number of players.
Since “tutti” already has a definition in the dictionary which is designed for the shipping sound set, if you wish to keep that intact, a good solution for NotePerformer playback of “tutti” is to go in Preferences > Word Menus > Techniques and add the following string to the “tutti” entry there: ~C104,0.
This way, the Playback Dictionary entry will be preserved and “tutti”will work correctly regardless of which sound library you are using. The Word Menu item should read as “tutti~C104,0” (the tilde hides the C104,0 MIDI Controller info in the score).
(Of course, if you only ever will use NotePerformer, you could simply edit the playback definition in the Dictionary to be Control Change > Controller 104, Controller Value 0. )
Don’t forget to export your current project as a House Style, so you can import your new Playback Dictionary entries into other scores.
That’s all there is to it!