The Doepfer A-199 Spring Reverb is a spring reverb module for modular synthesizers in Eurorack format. Spring reverb systems have a characteristic sound behavior based on the mechanical properties of the springs used - such as signal delays, self-resonances, limited frequency range, acoustic resonance behavior, sensitivity to mechanical influences. In the Doepfer A-199, a spring system with three separate springs is used, which makes the reverb very "dense" due to the different properties of the springs. As a special feature, the module allows the reverb signal to be fed back to the input, whereby the feedback can lead to self-resonance of the system. As a further special feature the module has an Emphasis control with which middle frequency ranges (center frequency approx. 2kHz) can be additionally boosted. The ratio between original and reverb signal at the mix output can be continuously adjusted with a mix control.