what is a univibe?

It's a vibrato, but not a chorus. I think it was intended to simulate a Leslie speaker effect on an organ; it really sounds more like a phase shifter effect than a chorus to me. You can hear it on lots of classic guitar tracks (Hendrix's "Machine Gun" is a great example).

 

It is a phase shifting effect. Most Univibes have a "chorus" mode and a vibrato mode. The "chorus" mode is the typical Univibe mode, and the vibrato mode is as it says, a pitch vibrato mode. So the "chorus" mode is actually a phase shifter, not a chorus as we tend to think of it, but it's also not quite the same as a phaser. To make a long story short, it is its own unique effect.

 

I've never used a vintage Univibe or Dunlop reissue on bass. I have used a Voodoo Lab Microvibe, which is Univibe-based I think. The Microvibe is fantastic on bass--tons of low end and dark, murky, and menacing, with OD/fuzz pedals or by itself...

 

ok, so what is pitch vibrato?

 

Here is a more in depth explanation by R.G. Keen from his "technology of...." series:

http://www.geofex.com/Article_Folders/univibe/uvfrindx.htm