ED102 - Octave-Volts-Hertz

Hertz/Volt (Hz/V) and Octave/Volt (Oct/V) "integrator"

Among presently available music synthesizers, there are two main different types of control system used for controlling devices such as the VCO (voltage controlled oscillator) and VCF (voltage controlled filter). These two systems been: Hertz/Volt (Hz/V) and Octave/Volt (Oct/V). To allow these systems to work together you will need a module like the ED102. The built-in, fully adjustable log amp and anti-log amp ensure complete system flexibility and compatibility between any presently voltage controlled synthesiser.

http://www.elby-designs.com/contents/en-us/p733_ED102_-_Octave-Volts-Hertz.html