Harmonic Enhancer

A harmonic enhancer is an audio signal processing technique that enhances a signal with phase manipulation, harmonic synthesis of high-frequency signals, and dynamic equalization. People also refer to this technique as exciter, harmonic exciter, or aural exciter. It adds a subtle harmonic distortion.

Harmonic synthesis creates higher-order harmonics from the basic frequency signals of a recording. Because sounds are perceptible at higher frequencies, the harmonics emerge from a purer frequency band, which translates into clearer highs. Aural exciters are able to synthesize the harmonics of low-frequency signals to mimic deep bass in small speakers.

Harmonic Enhancer: the Basics

Dynamic equalization includes a variation of the EQ characteristics in the time domain, such as a function of the input. Because of this, the sound reduction is pretty effective.

You can use enhancers typically during mixing and recording to treat individual tracks or sub-mixes.  They are also common during post-production, as well as in the mastering process. For instance, master tapes are a common example of this. The reason is that high-frequency enhancement helps compensate for the loss of clarity potentially achieved during the process of mass cassette duplication. Enhancers also add life to a poorly mixed master tape.

All said and done, harmonic exciters can enhance analog tapes that have lost their high frequencies due to ageing, repeated playing, or minor-head alignment. Producers frequently employ harmonic enhancement to make the lead vocal more intimate. This technique works well when trying to fix good recordings, as well as to fix poor poorly defined sound recordings.

Aphex Aural Exciter: an Example

One of the first commercially available units was Aphex Aural Exciter. It launched around 1970 and was quite successful. It added phase shift and musically related synthesized harmonics to audio signals. Many popular artists, such as Jackson Browne, The Four Seasons, Linda Ronstadt, and James Taylor used the Aphex Aural Exciter to record their albums. Nowadays, many manufacturers offer an improved version of it.