sir_analog (RSS)
"This amazing little device translates audio into VCO CV (control voltage) signals and trigger (gate) signals to control both Hz/V (Korg, Yamaha) and V/Oct (Roland, Moog, Octave, Arp, etc.) analog synths.
You can use an electric guitar, microphone, or other transducer output (from an acoustic instrument, for example) to "play" a synthesizer. A variety of remote control input jacks let you use foot switches for more freedom and flexibility.
What's more, it outputs positive and negative gate signals, ENV follower voltage, and has built-in portamento. So can be used to make automatic bass lines from drum machine beats and to sweep a synths filter from the envelope follower."