This video explains how you might use Blackstar's Infinite Shape Feature control, which is featured on the Series One.
The ISF is not a modelling feature, but along with the EQ controls, it can be used for emulating the sounds of other famous amplifiers.
It is a passive circuit, and is continuously variable. Changing the ISF doesn't scoop and over-ride your tone controls like a contour would. Blackstar are fairly vague on this matter, but the ISF changes the way that your tone controls react, so with the ISF cranked to ten, your tone controls would react more like those on an early Marshall amplifier. With the setting at 1, you would get closer to an American tone.
More From: BLACKSTAR AMPLIFICATION