I decided to make a new thread for this for the sake of clarity.

I'm new to Sibelius and VDL:2 and I ran into some trouble. Problems seemed to have ";fixed themselves,"; but I was finally able to recreate said problems. Doing so, I have discovered a solution that I haven't seen on these forums. Hopefully my post will help others in the future. This post is in reference to Sibelius 5.1.

[B]This post could potentially help you solve any of these problems:[/B]
- After making instrument changes, the new instrument won't play back (even after pressing ";play";).
- All of a sudden, <instrument> won't play back anymore - but it did before!
- <instrument> is playing back, but it's playing the wrong notes.
- Possibly more.



[B]Why this happens:[/B]
Each time you create a new instrument, Sibelius ";intelligently"; assigns it an appropriate MIDI channel. When working with Kontakt, Sibelius is limited to only 16 MIDI channels. For most people, this is fine since most people only write for the battery and/or a medium sized front ensemble. If you're writing for a large ensemble with all sorts of instruments, including various instrument changes, this can be a major problem. Each time you notate an instrument change, Sibelius has to assign it a MIDI channel. This is where problems start to happen.

All sorts of wacky things can occur. For example (but not limited to):
- Two separate staves of the same instrument type (example: 2 independent marimba parts) might end up sharing the same MIDI channel. This ruins the dynamic control over the two since they are on the same channel.
- An instrument that WAS working fine ends up on a different MIDI channel. This can cause it to play back the wrong notes or just not play back at all.

... So fundamentally, the problem is that you need MORE than 16 MIDI channels accessible to Sibelius, but you only have 16.



[B]Information before we solve the problem:[/B]
We need to tell Sibelius to run 2 (or more) instances of Kontakt. If this is hard to understand, think of it like running two ";slots"; of Kontakt, where each slot has 16 MIDI channels. You could even run three instances for even more channels. In fact, you could theoretically run as many as you'd like.

Something you should know:
Kontakt is taxing on your computer's memory and processor. The more instances of Kontakt you're running, the more memory (RAM) and processor resources are required. If you run too many instances, your computer will not be able to handle it and you'll have very poor audio quality (popping, hissing, skipping, etc).

[B]Solution:[/B]
Solution may vary on the Mac version. I'm not fortunate enough to afford a Mac, so I can't verify that this'll work on Mac. You are welcome to try, though! Let me know if it works!
In the Windows version:
- In Sibelius, close all your working documents, but keep the program open.
- Go to Play->Playback Devices
- Remove (deactivate) every item in the ";Active Devices"; list.
- Highlight ";KontaktPlayer2"; in the ";Available Devices"; list.
- Click on ";Activate"; and make sure it shows up in the ";Active Devices"; list.
- Double check that ";Tapspace Virtual Drumline 2.5"; is the selected sound set.
- Highlight ";KontaktPlayer2"; and add it again. This time, it'll be added with a number (2) after it.
- Again, verify that it's using the correct sound set.
- You may repeat this process to get as many instances as you need.

^^ Once this is done, all NEW arrangements will be affected automatically. Old arrangements need to have their instruments modified:
- Open the mixer window (Shortcut key: M).
- Expand the instrument that you want to modify by clicking the arrow on the left.
- Put your mouse over the pull-down menu underneath the instrument name. A tooltip should say ";Initial playback device.";
- Click on the menu. Select one of the KontaktPlayer2 instances. This instrument *AND* all instrument changes will now be loaded into the selected Kontakt instance.

^^ Tip: pay attention to how many instruments are being loaded into each Kontakt instance. Try to keep it balanced and **under 16 per instance of Kontakt**.



[B]Side notes:[/B]
This is a must have ";tweak"; for people that write for many instruments at a time. In terms of computer performance, I have a 1.6 ghz dual core CPU and 2 gb of memory and 2 instances of Kontakt run just fine.

Thanks for the post, but I don't think it's the best way to do things.  First of all, I think 16 channels is more than enough.  Here's what I use for a full pit+bat:

1. Marimba (shifted slightly right)
2. Marimba (shifted slightly left)
3. Vibes
4. Xylo
5. Bells
6. Piano/synth
7. Bass
8. rack A
9. rack B or Latin
10. Drumset
11. Timp
12. Snare
13. Tenor
14. Bass
15. Cym
16. open for whatevah

Even if your pit has 4 marimbas and 4 vibes, this will sound great.  The mallet players won't be playing the same part or in the same octave, so there's no need to load up the same number of tracks as you have players.

You can also solve your sound set problems by creating your own custom one.  You first have to enable custom sets in the program preferences and then restart it.  After that you can create your own and have more control over your instruments. 

Agreed.

Writing for a large group where varying instrument changes frequently occur must be considered. In this case, the MIDI channels are easily cluttered, especially with numerous auxiliary parts. If that is the case, then my post will help.