The attenuator synthesis application can be used to design various types of passive attenuators. Larger equipment will require an array of sound attenuators, otherwise known as an attenuator bank. Switching between different resistances forms adjustable stepped attenuators and continuously adjustable ones using potentiometers. Resistive components include terminations, resistors, and attenuators. Common circuit blocks which are two-ports include amplifiers, attenuators and filters. PIN diodes are useful as RF switches, attenuators, photodetectors, and phase shifters. However, distributed resistors may be used in attenuators and line terminations. Variable optical test attenuators generally use a variable neutral density filter. Special high voltage probes form compensated attenuators with the oscilloscope input. The semiconductor chip contains a decoder/encoder, loop backs, jitter attenuators, receivers, and drivers. There also exist optical attenuators that decrease the signal in a fiber optic cable intentionally. Electrical attenuators and optical attenuators are commonly manufactured components in this field. The optical devices include slits, attenuators, crystal monochromators, and mirrors. Typical improvements are vibration isolation of mechanical equipment, and sound attenuators in ductwork. Built-in variable optical attenuators may be either manually or electrically controlled.