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Aphex Aural Exciter Type C2

Article from Recording Musician, January 1993

Aural Excitement complete with the new 'Big Bottom' bass enhancer. A veritable feast of sonic titillation.

Aphex have made their Aural Exciter even simpler to operate and added a new feature which should really appeal to bass freaks. Paul White gets to the bottom of the Type C2.

For the benefit of those viewers at home who haven't yet experienced Aural Excitement first hand, I feel I should explain the basic concept before delving further into the model under review. Aphex first discovered the principle on which their Exciters are based way back in 1975, when the technology was shrouded in secrecy, and their first models could only be rented, not bought. Nobody knew exactly what the Exciters did, only that everything seemed clearer, brighter and more detailed. The effect was quite unlike anything that could be duplicated by equalisation and it seemed to work just as well on individual sounds as it did on complete mixes.

The reason why the Aphex Aural Exciter sounded so different to EQ is now obvious; unlike EQ, which can only boost frequencies already present in the original material, the Aphex system actually creates new high-frequency harmonics which are musically related to the existing material. In other words, even if the original sound is relatively dull, the Exciter can create a new, bright top end that is perceived as being a natural part of the overall sound. This process often comes under the banner of 'psychoacoustics', which is a another way of saying that it is based on a technological conjuring trick designed to fool the human hearing system into believing something that isn't actually real.

The technical trickery behind the effect is very simple. First, the original signal is split into two and one part passed through a high-pass filter so that only the upper mid and high frequencies remain, and then further processing is carried out to add harmonics to this signal by means of a circuit that creates controlled harmonic distortion. There is an additional dynamic element to this process which results in lower level, transient signals receiving more treatment, the end result being that the fine detail within any sound appears enhanced. The final step is to add just a small amount of this processed signal back into the original, unprocessed signal by means of a mix or balance control.

Until now, one weakness with Exciters was that the harmonic generation circuitry was very level sensitive, which meant that the user had to set up the optimum level by means of a Drive control and a simple LED metering system. Failure to do this resulted in either too little effect at one extreme, or audible distortion at the other. Fortunately, the type C2 currently under review has an internal level tracking circuit which avoids the need for a drive control, making setting up rather easier.

Traditional Aural Exciters treat only the top end of the audio spectrum, but other companies who have since produced their own psychoacoustic enhancers working on different principles have also included circuits to beef up the bass end. Obviously aware of this trend, Aphex have included their own bass enhancer in the type C2, and very powerful it is too. The Aphex design team are obviously Spinal Tap fans, as they've called this new system Big Bottom and have even gone so far as to trademark the term!


Housed in the now familiar 1U rack, the Type C2 seems rather lighter and less deep than its predecessors, due in part to the fact that Aphex have succumbed to the lure of the external power supply. The front panel design has moved away from the distinctive silver anodising and blue enamel that used to characterise Aphex products; it now has a grey enamel finish with white legend and mauve panels. Both the input and output connections are on jacks, switchable to accommodate -10dBv or +4dBu operating levels, and these may be used with either balanced or unbalanced systems. In the +4dBu position, the inputs are fully balanced by means of transformerless circuitry, while the outputs are pseudo balanced. This is a form of unbalanced circuitry that can drive a balanced load when called upon to do so. If the -10dBv option is selected, then the inputs are also pseudo balanced.

Ring for a brochure!

If you'd like more information on Aphex Exciters, UK distributors Aphex are happy to supply it. Just call Paul Scrivener on (Contact Details). Or write to him at the address at the end of the review.

The front panel control layout is quite simple and, like other Aphex Exciters, it is arranged as two discrete mono channels, though the bypass control affects both channels simultaneously. The first pair of controls relate to the Big Bottom effect and function independently of the Aural Exciter section. Reading between the lines, this process seems to be based on dynamic equalisation, which means that no new sub-harmonics are added, but the envelope of any existing bass frequencies is modified to make it appear louder. This, apparently, is achieved by extending the duration of bass sounds without unduly increasing their peak level, the degree of modification being set using the 'Overhang' control. An adjacent red LED flickers on and off to show how much dynamic processing is being applied. Like the Aural Exciter section, the Big Bottom process relies on adding a proportion of the treated signal to the untreated signal, in this case using the Girth control. So much for the bottom end — now it's time to see what's up top!

In the Aural Exciter section, there are two more knobs labelled Cleavage and Cup Size — oh, all right then, Tune and Mix! There's also a button pertaining to Harmonics, offering Normal and High positions. Tune sets the high-pass filter frequency, which determines the frequency above which the excitement will start, while Mix does as it implies and allows the harmonically-enriched signal to be mixed back into the main signal path. The higher the setting of the tune control, the narrower the area of the audio spectrum being enhanced.

The Drive control of the previous Exciters is conspicuously absent, but in order to provide the user with some control over the harmonic generation process, the Harmonics button has been added. In the Normal position, the treated signal is a complex blend of dynamic equalisation, phase shift and added harmonics which works well on most programme material. However, where the programme material is unusually dull or where a lot of brightness needs to be added to create the desired effect, the High setting provides a more harmonically rich processed signal. This really helps to pull sounds such as brass stabs, percussion and acoustic guitars out of a mix. Other than that, there's just a single bypass control which kills both the Big Bottom and Aural Exciter effects.

In Use

The Aural Exciter part of the system is subjectively similar to that provided by earlier Aphex Exciters, though the removal of the Drive control makes setting up a little faster. Used in moderation, the unit certainly creates the illusion of increased clarity, added brightness and better stereo definition, and even though I've been using these things for years, I'm still impressed at just how well they work. As always, you have to take great care not to overdo the effect, as you very soon get used to it, and then you're tempted to add more. The result of over-use can be a painfully bright mix, and any vocal sibilance also tends to be exaggerated, so discipline yourself to keep bypassing the unit and make sure that the amount of treatment really is fairly subtle. The easiest way to set it up is to turn the Mix control fully clockwise and then rotate the Tune control until the desired part of the sound is emphasised. The Mix control should then be backed off until just the right amount of enhanced signal is present.

Purists keep telling us that in a perfect world, with perfect studio equipment and a perfect recording engineer, Exciters would be unnecessary, but the fact is that we don't live in a perfect world, and even with the best studios and engineers, the instruments and voices being recorded often leave something to be desired. As ever, the end justifies the means, and if an Aural exciter makes a recording sound more appealing, then it's doing its job.

In the light of personal experience, I often find it most effective to treat only some parts of a mix rather than all of it, because this creates contrast. If you simply excite the whole mix, then the ear gets used to it and little is achieved. There are valid reasons for treating whole mixes, but the amount of treatment should be restricted to the absolute minimum. Situations where you might justifiably use an enhancer on a whole mix are: when recording with budget mics, when working with budget tape machines that have a limited audio performance and when mastering for cassette duplication to compensate for some of the top end that inevitably goes missing.

Used selectively, the Exciter can be used to brighten acoustic guitars, add intimacy to lead or backing vocals and to add sparkle to reverb returns. It works well on brass too, but don't make everything up front, otherwise there'll be nothing left at the back — some perspective is always desirable in a mix.

The new Big Bottom circuit has, no doubt, been developed in response to competing designs such as the BBE Sonic Maximizer and the SPL Vitalizer, the latter being particularly adept at massaging the bottom end as well as the higher regions. With the Type C2, there's no way to tune the process to any specific part of the bass spectrum, but for most types of pop, rock and dance music, the effect is fine as it is. Just a little adjustment and the bass end seems louder, more powerful and most definitely deeper — and providing you don't add too much, the rest of the mix remains reassuringly clear.

The Bottom Line

Aphex started the whole Exciter ball rolling, but over the past couple of years, I've had the feeling that some of their more innovative competitors were coming up with more attractive products, most noticeably, those that could be used to modify bass sounds as well as to add brightness. Now Aphex have bounced back with a vengeance with the Type C2. Those familiar with Aphex Aural Exciters will welcome the lack of a Drive control, but otherwise the subjective result at the high end of the spectrum is similar to that produced by the tried and trusted aural Exciters of the past. The charmingly named Big Bottom system would appear to be quite aptly titled, as the user now has independent control over the bass end of the mix too, and the dynamic equalisation system employed manages to dramatically increase the apparent depth and weight of a mix without adding much to the peak level.

Aphex Aural Exciter Type C2

  • Easy to Use.
  • Adds brightness and clarity.
  • Adds deep bass without muddying the

  • Separate Power supply.
  • Overuse can produce harsh mixes.


There are no complaints as such, though some form of tuning control for the bass enhancement might have provided a little more variety. The effect achieved is consistently very deep and solid, though I'd have welcomed an option that produced a tighter, more 'kicking' bass sound — perhaps a single button offering a choice of Pert or Flabby? However, that's a purely personal comment, and given the price of this unit and its usefulness on a wide range of material, I predict that it will become very popular, very quickly. Aphex have shown us that not only are they still on the ball when it comes to innovative circuit design, they've also hung onto their West Coast sense of humour. The Type C2 is a lot of fun and may well go down in the annals of studio history — I'll be sorry to leave it behind!

Further Information
Aphex Type C2 Exciter £269 including VAT

Stirling Audio, (Contact Details).

The Lowdown on Bottoms

When bass is boosted using EQ, the peak signal level increases dramatically and the signal can tend to become muddy, as boost is applied to all manner of bass and low mid sounds that might sound better left as they were. Aphex's Big Bottom circuit isn't based on simple EQ but instead, dynamically equalises the bass end of the spectrum using a process that is constantly changing the amount of boost depending on the dynamic of the incoming signal. Furthermore, rather than relying simply on dynamic boost, some frequencies are dynamically cut to maintain a subjectively clear sound, most of the processing taking place between 20Hz and 120Hz. The audible result is to 'stretch' bass notes, making them longer and subjectively more powerful, but without a significant increase in peak level. The Overhang control can be though of as offering control over how much the bass notes are stretched while Girth allows the modified bass end to be added back to the original signal.

Featuring related gear

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Mix Revolution

Publisher: Recording Musician - SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

The current copyright owner/s of this content may differ from the originally published copyright notice.
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Recording Musician - Jan 1993

Donated & scanned by: Mike Gorman

Gear in this article:

Studio/Rack FX > Aphex > Aural Exciter Type C2

Gear Tags:


Review by Paul White

Previous article in this issue:

> Tubular Balls

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> Mix Revolution

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