An exciter is an audio effects device that boosts high tones, thereby improving the reproduction of higher tones.
Exciters or enhancers are used in mastering and process signals by analyzing them and raising the level of high tones. This tone enhancement or generation of overtone spectra brightens and improves the sound image in the overtone range. The exciter technique is also used in the restoration of historical recordings but also in the reproduction of certain musical instruments.
Technically, it is a high-pass filter with a downstream distortion circuit that generates high- frequency signal components by harmonic distortion, in principle by overdriving the amplifier circuit. These harmonics are mixed back into the original signal at a reduced level, which results in the sound image having considerably more treble.