In auio processing, equalization (or equalisation, EQ) is the process of changing the frequency envelope of a sound. In passing through any channel, temporal/frequency spreading of a signal occurs. Etymologically, it means to correct, or make equal, the frequency response of a signal. The term "equalizer" is often incorrectly applied as a general term for audio filters. DJ mixing equipment and hi-fi audio components often include so called graphic equalizers or simply equalizer. These are in fact general all-purpose filters, which can be arranged to produce the effect of low pass, high pass, band pass and band stop filters. Only when these filters are arranged so as to reverse the effects of the internal circuitry on sound output, are they operating as equalizers.