In telecommunications, a spectral mask, also known as a channel mask or transmission mask, is a mathematically-defined set of lines applied to the levels of radio (or optical) transmissions. The spectral mask is generally intended to reduce adjacent-channel interference by limiting excessive radiation at frequencies beyond the necessary bandwidth.  Attenuation of these spurious emissions is usually done with a band-pass filter, tuned to allow through the correct center frequency of the carrier wave, as well as all necessary sidebands.