I’ve found with a few VST plugins whenever I open its GUI the CPU goes up to and stays at around 50-60%. This is showing in the Windows Task manager as the Renoise audio CPU meter stays at 0% when nothing is playing.
This is one of the problem ones - Compressive from http://martineastwood.com/wordpress/?page_id=153
Just tried both Compressive Lite and Compressive Pro, but I couldn’t really replicate the problem. I’m on Windows 7 64-bit with an i7 2.0GHz CPU and 8GB RAM. Tried in both Renoise 2.8 32-bit and Renoise 2.8 64-bit. No real difference in overall performance.
Could you give some more details about your system and setup?
That’s strange.
I’m on Windows 7 64 bit. A lowly AMD Athlon 64 X2 2.4 GHz with 4 GB RAM. Running Renoise 2.8 32 Bit.
I thought at first it may be something wrong with my graphics drivers but if I open the same plugin in FL Studio it only adds a few % to the CPU opening the GUI.
That’s very strange indeed. I can barely notice any difference at all when using the plugin. If anything, Renoise seems to consume less CPU when the GUI is open, haha.
I’ve tried experimenting with sandboxed vs non-sandboxed plugins (Prefs > Plug/Misc - you’ll need to reload your song or the plugin for the change to take effect), and I’ve also tried toggling the various plugin compatibility settings (the [?] button in the DSP Chain), but nothing seems to make any difference here.
Perhaps you can try experimenting with those options to see if it makes any difference for you?
You can also right-click Renoise’s CPU meter to override the number of CPU cores that are used. It some rare cases it can help to set only 1 CPU.
Unfortunately I don’t have an AMD CPU here to test with, but maybe another user here can give it a try.
A bit of testing with the options:
The ? - Use static buffers/Multi processor did not make any difference (did reload the plugin after changing)
Plug/Misc - Enabling sandboxing reduced the CPU to ~ 34%
GUI - Unticking the Framerate (was set to 60) reduced the CPU to ~ 40%
I sometimes have this problem too , but it really depends on which plugin I use ,
In the past I used to use a lof of cracked software and the problem occured more then now , now I am almost 99.99 pct legit … and occasionaly there are some plugs that really take a lof of cpu use ( graphical wise ) the demoversion of fx pansion 'etch ’ for example …
I just tried Etch and it uses hardly any CPU when it’s GUI is open. My system must be wonky 
The same is with some melda plugins (those with moving elements) - http://www.meldaproduction.com/freevstplugins/mcompressor.php for example.
One loop + mcompressor without gui:
http://www.fotosik.pl/pokaz_obrazek/pelny/f10b9b60e5a4e515.html
and with gui
http://www.fotosik.pl/pokaz_obrazek/pelny/4a48ac40fffa4b4a.html
It`s constant - not spikes. Checked with main unit (dual core, 2g ddr2, p45, rad hd6750, win7 32b) and laptop (Ibm x61 dual core, win7 32b and winXP).
Edit: Audio Damage - Replikant is another one