Here is article from Sonar X3 manual (New features in SONAR X3-> VST enhancements):
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VST3 plug-ins provide several benefits over VST2 plug-ins, including:
● Improved CPU performance. VST3 plug-ins can detect silence and automatically disable processing if there is no input signal. This allows for more efficient CPU use because processing is only used when needed.
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VST suspending works fine with my Waves VST3 plugs on Cubase 7!
I have sent  request to the tech support, but still no reply!



 

You don't need to do anything (if the plug-in supports it).

KPerry
You don't need to do anything (if the plug-in supports it).

Tested VST3 plugs supports it (tested on Cubase 7)
It is not working on Sonar X3 - tested VST3 plugs always takes CPU power on Sonar X3d.
 

Please list the specific plugin and exactly how you are testing it. The plugin must support this and the host has to be streaming silence to the plugin for it to take effect.

which plugin(s) are you testing with?

Noel Borthwick [Cakewalk]
Please list the specific plugin and exactly how you are testing it. The plugin must support this and the host has to be streaming silence to the plugin for it to take effect.

Tested plugs (with intensive CPU usage, without sidechain input):
1.Waves Kramer Master Tape VST3 Stereo
2.Waves Masserati GRP VST3 Stereo
 
Reproducing:
1. Create new project from "Normal" template.
2. Insert Waves Kramer Master Tape VST3 Stereo into existed empty audio track ( Input=-none-, Output=Master)
3. Wait 1 minute
 
Result:
CPU~15%
 
 
In Cubase 7 when the silence flag arrives to the input , plug-in goes to sleep mode after 5 sec 
 
 
 

It seems nobody needs VST3 interface full support on Sonar X3, even when Steinberg dropped VST2.4!
:(

Forget the forum, get on the phone to tech support.

Still no solution from tech support since January 8th 2014 

As far as I can see we are following the VST3 specification and passing on the silence flags to the plugins.
I will follow up with Waves engineering and see if I can get some feedback from them. Thanks.