Harmonic Enhancer

What Is an Exciter?

An exciter (a harmonic exciter or aural exciter) is an audio signal processing technique that enhances a signal by dynamic equalization, phase manipulation, and harmonic synthesis of (usually) high-frequency signals. It also adds subtle harmonic distortion. Dynamic equalization involves a variation of the equalizer characteristics in the time domain as a function of the input. Due to the varying nature, it reduces more noise compared to static equalizers. Harmonic synthesis involves the creation of higher-order harmonics from the fundamental frequency signals present in the recording. The harmonics are derived from a purer frequency band because noise is usually more prevalent at higher frequencies. This results in clearer highs. Exciters can also synthesize harmonics of low-frequency signals to simulate deep bass in smaller speakers.

Treating Master Tapes

Although enhancers are often used during mixing and recording to treat individual tracks or sub-mixes, they are also used during mastering or post-production. A common practical example would be to treat master tapes. High-frequency enhancement can help to compensate for the loss of clarity inherent in mass cassette duplication. To a lesser extent, this process can add life to a poorly mixed master tape. Additionally, it can treat an analog tape master that has suffered a loss of high frequencies because of repeated playing, aging, or minor head-alignment during the recording process.

Harmonic Enhancement

Producers use Harmonic enhancement to make the lead vocal more intimate. However, it's necessary to avoid sibilance as any form of high-frequency enhancement. Conventional EQs tend to exacerbate sibilance problems. Harmonic enhancers work well on poorly defined drum sounds, electric pianos, and acoustic guitars. However, using them to augment an already good recording is always better than relying on them to fix up poor recordings.

Harmonic Enhancer History

Regarding the history of harmonic enhancers, one of the first successful commercially available units was the Aphex Aural Exciter, first presented in the 1970's. Aphex Electronics developed this effect in the mid-1970s. The Aural Exciter adds phase shift and musically related synthesized harmonics to audio signals. The first Aural Exciter units were available in the mid-1970s, exclusively rented. In the 1970s, recording artists, including Jackson Browne, The Four Seasons, Linda Ronstadt, and James Taylor, recorded their albums using the Aphex Aural Exciter.

Apex Exciters

Aphex started selling the professional units and introduced two low-cost models, Type B and Type C. Today, a growing list of manufacturers, including Yamaha, MacKenzie, Gentner, E-mu Systems, and Bogen, are building the Aural Exciter circuit. The original Aphex Aural Exciter did not have the Big Bottom circuit. It was added in 1992. Later revisions of the Aphex Aural Exciter included the Model 104 Type C and Type C2 units. Aphex released 2001 the Model 204 Aural Exciter and Optical Big Bottom, yet another refinement of the original unit. According to Aphex, the Model 204 updates the Aural Exciter and Big Bottom processor blocks with improved circuitry. It also includes an optical gain-control element for the Big Bottom compressor.

Additional Resources & Source Texts

Exciter Effect