pre-emphasis
/priːˈɛmfəsɪs/Chiefly Sound Recording and Broadcasting
noun
A systematic distortion applied to an audio or video signal prior to transmission or recording, usually in order to improve signal-to-noise ratio, involving an increase in the relative strength of certain frequencies in anticipation of a corresponding decrease (de-emphasis) made during reception or playback.
Origin
1940s; earliest use found in RCA Review. From pre- + emphasis.