A single triode stage circuit typical for guitar preamps is captured in this plugin. The model engine is based on a system of non-linear ODEs. Some smart calculation techniques are used to reduce the computational load.
This effect could be used to apply mild tube overdrive to add some presence to your tracks, or you could chain a couple of instances together for a full-blown high-gain overdrive. You may want to throw in some EQ as well to better shape the signal and use a poweramp/speaker simulater afterwards.
The plugin UI has a real-time transfer characteristic plot display. It provides an overview of the things going on inside the tube. It also has a peak-detecting algorithm that will flash a line when the level exceeds 0dB. You can monitor stereo channels separately or at once by clicking the corresponding buttons under the plot display.
16x switchable oversampling is also implemented to reduce the aliasing effects. Please note that for the most time the aliasing is low enough to switch off the oversampling. When oversampling is enabled, the plot display will not be of much use, because of the phase smearing introduced by the oversampling filters. Still good enough for monitoring the in/out levels.
SoftAmp 3OD is available at no cost (freeware).
More info: SoftAmp 3OD VST