I asked a question similar to this a long time ago and the response I got from VSL was that it is generally less taxing on a system to host individual VI instances in a single VE instance rather than having say individual VI instances for Violins then another instance for 2nd violins, Violas, etc. The samples also load faster if you have to leave the project and come back to it later.

Also, the advantage to using VE to host your VI's is that you can build and save templates (Strings, Brass, etc) which can be used again and again for future projects so as to avoid the necessity of having to reinvent the wheel time and again.  Does that make sense?

There is no reason to use multiple instances of VE unless you want to keep groups of instruments separate for some reason.  Like one might use a Dimension strings group on a different computer so then it would make sense because it is easy to move all at once.  But unless you are doing some very arcane separate treatment of groups of instruments, it makes no sense otherwise to use multiple instances of VE since it is basically designed to host VI instances - that is the whole point of VE - and has no limit on the number of instruments other than CPU/memory.  

The main reason I use 3 or 4 instances if it's this large a project is I do extensive automation, and distributing that visually in Cubendo is better because I can minimize instances and just be looking at one; all four is scrolltastic. I would be pushing the limit of parameters lately, as well.

from p24 of VEP 6 Manual English v3.1:

"Vienna Ensemble Pro Server will generally perform best when running as few instances as possible."

I would suggest reading the section A Note on Multiprocessing on p24. It talks about how you should configure # of threads if you want to use more than 1 instance.

Anyway, my reading of it is your default should be 1 instance, and if you want more instances to support your workflow then go for it. But multiple instances is purely for workflow, not for performance gains.

Thanks for that clarification.  And that makes complete sense...  If nothing else, the threads per instance perference will have a much more optimizing effect with one instance.  For example if you're using 4 instances on a 12 core system, then you probably need to set that pref to 5 threads, give or take.  If you have one instance, then you could set it to 20 threads.  In the 4 instance case, if two instances are sitting idle, the other two active instances are then allegedly only using 10 threads, when 20 could be available.  etc..  using a single instance lumps them all together instead of having to divide up the resources.  So to me that seems VEP is definitely written to work somewhat more efficiently with a single instance.

On top of that, if you have multiple instances, then you will have multiple VEP plugins in the DAW communicating at the same time in parallel to 4 different instances in whatever manner it does through interapplication communication.  With only one instance, then there is a lot less of that communication overhead.

Aside form workflow desires...many in the LogicPro camp are forced to use multiple instances...in some cases MANY multiple instances to get around limitations in LogicPro where it doesn't support multiport.  So there is that too.  

@jorisdeman said:

the options are:

-Fewer instances of VEP connections (in the DAW), with many VI's in one instance on the Slave (requiring lots of outputs and midi channels)

I do from 2 to 4 stereo outs, that's my preferences setting, '8 Audio Outputs'; I mix using Automation in VE Pro and typically I do print some channels but not en masse; so this is my use case, I print the instrument's channel and its return in the Master channel as a wet channel for mixing. A less demanding aspect is I may want some control over the Instrument Channel in Cubase individually at the level of Master (where the instance's reverb resides); Pitched; Percussion; and sometimes another special one. I find that a lot of Audio Outputs (or Inputs) uses CPU to an extent I would rather not do since there's not real need.

I'm using for Rock-n-roll, moslty effects and some VST instruments.  With that said, Cubase is a pain because if I put 1 instance with 5 different reverbs on different outputs, in Cubase, if I turn off an output for the Epro instrument track, it will rename it back to "output 1/2" - 

What I mean is - once i turn on an output for the Epro output, in the mixer i can rename it from "output 1/2" to "Roomworks".  But if I turn off that output, Cubase clears the name because it's no longer in the mixer.  If I turn them back on, Cubase doesn't remember the previous name - it renames it back to "output 1/2".

Thus, I'm sort of forced to create 1 instance for 1 effect if my names in Cubase are to remain.  I say this because I don't want to turn on tons of outputs in Cubase.  But if I turn them off, then all I see in the mixer is "output xx".  PAIN!

So I'm guessing 20-30 instances may be the way to go.

Any suggestions?

You didn't say why you keep turning off outputs in the Cubase rack. Yeah, stop doing that, if that's creating a need for all these instances, it's not a need. You can simply disable a channel in VE Pro that you don't need or simply disconnect from the instance, which does not take it out of the mixer. What you're doing, you may as well just plug the reverbs into Cubase.

Along this topic of honoring a 1:1 ratio of instruments to players for performance/CPU threading reasons ... what if you had, for example, four instruments in a Kontakt Multi, 4:1, but only one is used at any one time. Would you still get the thread you desire, or do you really need the strict 1:1 ratio?

AnyKenny,

Yea, that's the question in a nutshell.  I'm currently running abotu 15 instances for effects busses and it's working just fine.  But I'm going to try doing about 40 (1 effect per instance) and see if I get any different performance (audio pops,clicks / latency).

I'll post up whatever happens.

Aug

One other question on this issue:  Does turning off instances change anything regarding CPU load?

So I'm using about 33 instances and I don't see any cpu load issues at all.  Stable. 

I'm using 1 effect on 1 instance for FX bus in Cubase.