MOTM

Does anyone know a simple circuit I could build to drop an input voltage
in 1 volt steps. What I want to do is build an oscillator controller to
switch octaves by flipping a series of switches or by turning a rotary
switch. I'd like to be able to tune all my VCO's the same and then use
this unit to lower the pitch by octaves, similar to the footage switch
on a moog 921. Is this possible? -Nate