Tech 21 SansAmp Version 2 Specifications:

• PRESENCE: Controls the amount of definition and upper harmonic content.
• DRIVE: Adjusts the overall gain structure and overdrive.
• LEVEL: Regulates the XLR and effected 1/4″ output levels.
• BLEND: Allows you to mix the direct bass signal with SansAmp Tube Amplifier Emulation circuitry (which is particularly useful for basses equipped with piezo pickups).
• BASS & TREBLE: Are active EQ controls, specifically tuned for bass guitar, that cut or boost +/- 12dB.

The updated version of the SansAmp includes an added switch that adjusts bass frequency to extend into lower registers, as well as a mid-range control witch switch to adjust the frequency.