In electrical systems, a network that reduces the amplitude of a signal without appreciably distorting its waveform. Note 1: Electrical attenuators are usually passive devices. Note 2: The degree of attenuation may be fixed, continuously adjustable, or incrementally adjustable. Fixed attenuators are often called pads, especially in telephony. Note 3: The input and output impedances of an attenuator are usually matched to the impedances of the signal source and load, respectively. 2. In optical systems, a device that reduces the amplitude of a signal without appreciably distorting its waveform. Note 1: Optical attenuators are usually passive devices. Note 2: The degree of attenuation may be fixed, continuously adjustable, or incrementally adjustable.