A measure of the ability of a receiver to discriminate between wanted and unwanted signals. This is of particular importance when dealing with wireless mic systems, where you want to pay close attention to a signal on one frequency while not listening to an adjacent frequency. In wireless receivers a bandpass filter is used to reject all radio frequencies – including broadcast radio and television signals – that are outside the band assigned to its system. To measure the selectivity of filters, designers of wireless systems use a rating they call “quality factor,” or Q. The higher a filter’s Q, the greater its selectivity in isolating frequencies. Selectivity is expressed by the amount of signal rejection above and below the operating channel the receiver will provide.