Saturation Knob is the analog sounding, simple to use, yet versatile way of adding some sweet distortion to your tracks. The knob itself controls the amount of saturation, and there are three different distortion characteristics to choose from by flicking the switch.
With the switch set to Neutral, the entire frequency spectrum of the sound gets distorted when you turn up the Saturation knob. Put it on Keep Low, and the saturation will mainly affect the lower part of the frequency spectrum, while the top end stays clear. Conversely, with Keep High selected, the low end will retain its clear sound and instead only the treble parts of the sound will get distorted. This makes a wide variety of distortion characteristics available to you.
Saturation Knob is available for free as AAX plug-in for WIndows and Mac OS X at Avid.