A technique used to improve the signal-to-noise ratio in a radio-communication system that employs frequency modulation or phase modulation. A network that increases the modulation index of the higher modulation frequencies relative to the lower ones is inserted at the transmitter. De-emphasis is used at the receiver in order to restore the relative strengths of the audiofrequency signals, i.e. a network is inserted that reduces the relative strength of the higher frequencies. Amplitude-modulation systems rarely use pre-emphasis and de-emphasis as the resulting improvement in signal-to-noise ratio is only slight.

The technique is also used for magnetic tape recordings, gramophone records, and speech analysis systems to counter the average –6 dB per octave spectral tilt found in speech and music.