Reverb units simulate sounds produced in a finite acoustic space by creating a large number of echoes that gradually fade or "decay". One early technique for creating a reverb effect was to send an amplified signal of the music to room with reflective surfaces, such as a tile bathroom, and then record the natural reverberations. A plate reverb system uses an electromechanical transducer to create vibrations in a plate of metal. Spring reverb systems, which are often used in guitar amplifiers, use a transducer to create vibrations in a spring. Digital reverb effects use various signal processing algorithms to create the reverb effect, often by using multiple feedback delay circuits.