A circuit that arithmetically adds two voltages, producing an output signal whose voltage is the sum of the two input voltages. For instance, to take a two-input adder, if one input is at 1.7V and the other is at 0.5V, the output will be 2.2V. An example usage for a voltage adder is to (assuming a volts/octave synth architecture) process a control voltage output from a sequencer that is driving a voltage controlled oscillator to play a repeating melody. By adding, say, a control voltage from a keyboard to the sequencer's output, the performer can transpose the sequence to different keys by pressing a key on the keyboard.