Oh yes, the native CPU munching enigma. Scott is right, it depends on your PC, Soundcard, buffer-size and most of all DAW host software. I had (37) Neve 88rs channel strips going in SONAR 6.2.1, using about 45%
total DSP across (4) UAD-1 cards and the native CPU munch would rear it's ugly head when I repeatedly stopped & resumed playback. The Task Manager would show the native CPU go from about 20% to 60%-70% or more. I would also get an instant dropout when I reached the end loop point of an enabled loop region.
But then, using the exact same computer and project wave files, but using
REAPER, I was able to get (57) Neve 88rs instances going and the native CPU stayed steady @ 15%-18%, no mater how many times I stopped and resumed playback. In addition, smooth seek and project looping, during playback is flawless.
So guess which DAW host I use when I mix with my UAD-1 plugins?
Now there will always be some native CPU usage when using the UAD-1 plugins, but in optimal situations it should remain negligible, at worst.
Using REAPER, at 1024 samples (23.2msec) project latency, each UAD-1 plugin uses and average of .12% native CPU, on my Core Duo (e6300) DAW. Which equates to about 3% total native CPU usage for (25) UAD-1 plugins in a project. Which is pretty much insignificant.