A harmonic exciter (or 'enhancer') is often applied to a track during the mastering process to help add that final piece of 'sparkle' to a mix. By applying this type of processing, the overall resolution of the music can be artificially increased, resulting in a sonically brighter final product.

The primary function of a harmonic exciter is to restore or replace any frequencies that may have been compromised or left out altogether during the mixing stage. This can often be attributed to other processing which has been applied to the various tracks, consequently dulling many of the transients due to various changes in phase. One way an enhancer can resolve this issue is to realign the phase of the transients, which helps to restore their definition and therefore increases the general clarity of the music.

Another way that exciters can improve the brightness of sound is to introduce reasonably small amounts of harmonic distortion. Particular frequencies can be targeted by adjusting the controls, and the exciter will treat the sound by subjecting it to second and third order harmonic distortion. This distortion is then mixed back in with the original signal, resulting in a much cleaner and brighter sound.

Many modern harmonic exciter plugins are multi band, which allows the user to apply different amounts of enhancement to different frequencies bands. As the aim of an exciter is to artificially increase the brightness of the high frequencies, and the density of the medium to low frequencies, it is important that these can be treated separately. Multi band variants are therefore very flexible in these situations.

It is important to use enhancers diligently, especially if applied across the whole mastering bus. Overuse of this type of processing can often result in a fatiguing and overtly unnatural sound which is unpleasant to the listener.

Article Source: http://EzineArticles.com/?expert=Alex_F_Gray
http://EzineArticles.com/?Harmonic-Exciters&id=3659389