Keyboard+little box=synth sound?!?!

[Jiffy]

I was at a party the other day and the girl's dad had set up some sort of keyboard which was then hooked into a little black box.

the black box had probably 3 knobs on it, and one of them could change the sounds from synth/piano/strings/etc.

so, i was wondering how do you do this?

is it a midi controller hooked into some sort of midi sound box?

[Mother]

was the black box connected to a pc?

[Shadows Within]

either a midi sound box or a really small synth module, i have a JV-1080 and its rack size with a whole bunch of buttons but i've never heard of one with 3 knobs...