The Doepfer A-114 is a dual ring modulation module for the Eurorack A-100 system Ring modulation is a classic modular effect that adds bell like or chiming tones to the audio signal. A ring modulator outputs the product (Multiplication X • Y) of the signals at inputs X and Y. It's similar to a VCA, but whereas a VCA only responds to positive voltages at the inputs (2-quadrant multiplication), the ring modulator responds to both positive and negative voltages (4-quadrant multiplication).