Abbreviation for “Function.” A component of the V.A.S.T. synthesis architecture found on Kurzweil K-Series synthesizers, beginning with the K2000 in 1991. FUNs are a series of equations you can use to modulate control-source signals, from physical MIDI controls like the Mod Wheel to software control sources such as LFOs and attack velocity.
FUNs take these control sources one level further. By setting up a FUN as a control source, you can mix the signals of two control sources, and perform one of many functions on the combined signals. The result of that function becomes a new control source value. Because they can radically change their combined input values, FUNs can have a profound effect on sounds.
FUNs combine two different control source inputs, such as an LFO, a MIDI controller, a numerical value, or even another FUN. For example, the FUN equation sin (a+b), where a is an LFO and b a numeric value, can transform a sawtooth wave into a smooth sine wave or an extremely complex waveform, depending on the input value.
You can access FUNs by entering the Program Editor, then using the soft buttons to select the FUN page. The best way to understand the use of the FUNs is to set up a simple test model (say, a single-layer program built on a dull sawtooth wave), then plug in the different equations and listen to their effects. The more you play around with FUNs, the better you’ll understand how powerful they are.