Here's what Cornerstone say about the Sparkle:
The Sparkle overdrive has been designed out of a need for a super touch sensitive overdrive that could exactly follow the playing of the guitarist without turning any knob during songs. The design goal was to create an extremely easy to use yet still dramatic and versatile overdrive.
Looking at the controls, there are Volume, Gain, Bass and Treble. The Volume control acts as a master output level control. The Bass and Treble controls manage the frequency responses of the pedal. With both set at noon, the Sparkle creates a flat frequency response, When adjusting the tone controls, the sound always stays full and well-defined without ever getting muddy or gloomy.
The 9v/18v switch allows the guitarist to choose which voltage the circuit would be supplied with, still using the same external 9v power supply. In 18v mode, the pedal offers a lot more headroom than the standard 9v, which is extremely useful for guitars with more powerful pickups.
The Sparkle requires a standard 9V DC Negative power supply only.