HARMONIC PARTIALSHarmonic partials or "harmonics", are timbres whose frequencies are integer multiples of the fundamental frequency of a given sound. The goal of harmonic excitement is to recreate the psychoacoustic effect of these additional frequencies in order to restore the brilliance lost due to limitations inherent in many recording mediums. In most cases a combination of equalization and distortion are used to achieve this effect, though the exact process will vary depending on the manufacturer.
A UNIQUE SOLUTIONWhile equalizers allow us make timbres brighter or darker by boosting or cutting relevant frequencies, they fall short in one area in particular, in that they are not capable of boosting something that isn't there, and as a result, they can only do so much when working with low-frequency timbres such as sub-bass. As many of us know, large high-frequency boosts on an equalizer will not necessarily brighten a sound in the way we would like it to. Boosting higher frequencies may also introduce what is known as "hiss" and undesirable sibilance, particularly on vocals. As a result, one way to brighten timbres in a mix is to employ the use of an exciter or enhancer. Harmonic enhancers are audio signal processors that enhance a signal through a combination of dynamic equalization, phase manipulation, and harmonic synthesis, and subtle harmonic distortion. Harmonic synthesis is a process by which higher order harmonics are added to the fundamental frequency of a timbre.
BRIEF HISTORYThe first harmonic excitement processor was claimed to have been developed by accident. Engineers who later formed the company Aphex, claimed to have assembled a tube amplifier incorrectly, so that one channel was clean and the other was thin and distorted. By combining the two channels, they noticed a much clearer, more present sound. This excitement processor was initially very secretive in how it achieved its effect. Studios would actually pay Aphex engineers to come in and setup their system for use on their mixes, and it is rumored that many studios even had to pay royalties on top of up-front fees for the service. Aphex made a big impact on the recording industry as a result of their discovery, and their patented Aural Exciter is legendary as a result. Since that time, however, many other companies have introduced their own lines of enhancement and excitement processors, all using different methods of processing to achieve their sound.
MODERN ITERATIONSSound Performance Lab, better known as SPL, is a manufacturer of high-end audio hardware and software based in Niederkruechten, Germany. Their processors are incredibly popular due to both the sonic quality they provide, in addition to the availability of affordable software plugins. SPL's Vitalizer is perhaps the best example of a modern harmonics processor, and purchased as a software plugin for about $100. The Vitalizer operates by combining a processed side-chain signal to the main signal. Though the specifics of how the Vitalizer processes the side-chain signal are quite complicated, the process for the most part involves equalization, subtle phase shifting in the low and mid-range frequencies, such that when added to the original signal the sound becomes brighter and more in focus. Another useful feature on the Vitalizer allows for the user to isolate the side-chain signal, so that it can be heard separately from the main signal. The resultant effect not just at the top end, but across the whole frequency spectrum. Processed mixes feature an increased sense of loudness, clarity and detail. As an example of a great harmonic exciter, the Vitalizer provides an easy way to add warmth and punch to a mix that most people associate with high-end analog hardware.
Another enhancement processor which unlike the Vitalizer, is designed to work only with low-end bass processing, is Waves' MaxxBass. This processor is only available as a plugin, though it does a great job of bringing low-end material to life using similar methodology to most other enhancement units. MaxxBass analyzes an incoming signal and adds higher frequency harmonics, the level of which may be adjusted by the user to taste. The beauty of this plugin is that it keeps the original bass timbre intact, and adds enough harmonic content so that listeners on small limited-range speakers can still hear the low-end bass movement due to the artificially generated harmonic content.