Aphex have ported their expertise in spectral processing to a range of guitar pedals that also double as DI boxes. Currently there are models for acoustic guitar, electric guitar and bass, all housed in similarly-styled but differently coloured cast metal cases. Power can come from batteries or an external power adaptor (optional) and the output is available on both unbalanced jack at instrument level and balanced XLR connector with a ground-lift switch.
The XLR output is designed to feed a balanced mic preamp, such as a mixer. This DI output has a switch that allows it to be configured with or without the effected signal added. Apparently the external power system has been designed so that it can accept any polarity (or even AC) and it works over the voltage range 5-12V AC or 7-17V DC. When running from a 9V battery, the current draw is only around 5mA, so the battery life should be reasonable. The instrument input is switchable between a high-impedance jack optimised for use with passive pickups or a medium-impedance one for use with active pickups. The Acoustic pedal has a particularly high impedance (10M(omega)) for use with passive piezo pickup systems alongside a lower impedance for use with active electronics.
All three pedals use variations on the same Aphex circuitry to provide high-frequency enhancement based on harmonic generation, plus the dynamic 'optical' Big Bottom circuitry. This is tuned differently for the different models, so that for acoustic guitar it emphasises the body tones, for electric guitars it provides an alternative tone colour for the lower notes, and for the bass guitar it makes the notes sound deeper and more powerful. The Big Bottom process is a form of dynamic equaliser based around an optical limiter circuit, and phase shift also figures in the equation. The Lo Tune control sets the upper frequency limit for bass enhancement, while Lo Blend determines how much of the effect is added. Because the effected signal is added to the original, the effect is that of lifting low-level signals rather than squashing the peaks and, because of the limiting element of the circuitry, the peak level doesn't increase significantly, even when the perceived level of bass has increased quite dramatically. The Lo Tune range is 40-210Hz for the Acoustic model, 30210Hz for the Bass model, and 40-210Hz for the Guitar model.
The Aural Exciter part of the circuit has a Hi Tune filter control, which sets the point above which enhancement takes place, and there's a Hi Blend control to regulate the amount of harmonics added back in. The Hi Tune range is 300Hz3kHz for the Acoustic model and 500Hz-5kHz for the Bass and Guitar models. All have a quoted signal-to-noise ratio of 70dB, and when the bypass button is operated, the input is routed directly to the instrument output.
As expected, all three devices behaved similarly except in the range of frequencies covered and, on the whole, they did exactly as claimed. The degree of bass enhancement can be dramatic, and is surprisingly effective for bringing out the body tone in the acoustic guitar — and of course it adds considerable depth to bass guitar sounds. The Aural Exciter part sounded much as I expected, as I've used many Aphex devices over the years, and, provided that you don't set the Hi Tune control too low, you can add a nice sense of air and detail without roughening up the mid-range. At lower settings it can become harsh, but then too much range is always better than not enough. When used to DI clean electric guitar, the process adds a nice zing to the sound as well as filling out the low end, but again the Hi Tune control setting shouldn't be set too low. My only slight reservation was that the Acoustic pedal, used with my active acoustic guitar, sounded quite different when bypassed to when active, even with the processing depth turned right down. This had the effect of hardening up the sound somewhat, but I suspect the effect differs depending on what preamp you're using and what amplifier you're feeding it into. The acoustic sound can be made brighter and weightier in a reasonably flattering way, but you have to be careful to add only as much processing as required. Too much can sound hard and harsh again.
These little pedals do exactly as claimed and, though the user has to exercise restraint in how much effect is applied, having two knobs for the bass end and two for the high end makes things simple to use. In addition to providing tonal adjustment beyond what can be achieved using EQ, the DI facility is a great bonus both for live work and for recording. I also feel the Bass pedal may be useful for those people who want to process synth bass sounds to make them appear bigger and deeper, but without taking up any more headroom. If you want the genuine Aphex sound in an instrument-friendly package, this is the answer.