How do you make a piezo‑miked acoustic guitar sound like a 'real' miked acoustic? Fishman have improved on their already impressive answer to that question...
Fishman's original Aura system was developed to improve the sound of acoustic guitars fitted with piezo‑electric pickups, and has much in common with the 'fingerprint' equaliser plug‑ins used in the studio. The theory is that if you measure the frequency spectrum of the original instrument both via its pickup and miked up, it should be possible to compute a complex EQ curve from these 'images' to make the DI'd instrument sound as it would if miked. This is just one of the technologies that can be brought to bear on the problem, though, as it's possible to further refine the process by manipulating the phase and even the volume envelope of different parts of the frequency spectrum. Fishman, of course, don't reveal exactly which techniques they use, but the results have usually been pretty good.
The Aura Spectrum combines a DI box with Fishman's Aura Acoustic Imaging technology and uses 24‑bit audio converters with 32‑bit processing. Power can be drawn from a 9V DC external power supply or an internal 9V battery — and an alkaline battery is expected to last over 20 hours. The device is designed to work with both under-saddle piezo and soundhole magnetic pickups, and has potential applications both live and in the studio.
The device includes a three‑band equaliser, a chromatic guitar tuner, a simple 'more or less' compressor, and even automatic feedback suppression, which is based on three tracking notch‑filters and a phase switch. Further controls allow adjustment over the blend between the raw pickup sound and the processed sound, and connections include an effects loop for patching in additional processors or effects. The DI output is via a balanced XLR connector, and there's a ground‑lift switch to combat ground‑loop hum. It's also possible to process a line‑level signal, so instruments previously recorded with a pickup can be re‑processed using the Aura Spectrum DI — a useful feature.
That's all conventional enough, but, as with other Fishman Aura products, what makes the Aura Spectrum a bit special is the way in which it uses the acoustic Images, and the number of Images available. The device comes with 128 pre‑loaded images, and amongst these are many popular acoustic stringed instruments (not just guitars). Of the 128, 16 are user-configurable, via a USB connection and the bundled Image Gallery III software.
The software (and the USB connection) works with both PC and Apple Mac computers. When I first started this review, only the Windows version of Gallery was available, and when the first Mac version came online, it turned out to have a problem with some Macs — including mine! However, the latest version (3.2.3) seems perfectly stable.
The Aura Image Gallery includes a large library of images of instruments with different miking arrangements. Currently, there are over 700 Images of guitars (including 12‑string models), plus a range of other stringed instruments that might be used with pickups — such as mandolin, violin, resonator guitar, bouzouki and ukulele. It's even possible to have Fishman make a custom Image of your own guitar at additional cost, after which time it will be added to the library.
Rather than listing all instruments only by manufacturer's name and model number, they're also classified by body style, the woods used and the make and position of microphone. Usefully, if an Image isn't present for the instrument being used, the player can use an 'Image Wizard' to find the one that's the closest match to it, by entering details such as body style, wood type, and so on.
Packaged as a high‑class, all‑metal stomp box, the Aura Spectrum has two footswitches towards the front edge for selecting the tuner and anti‑feedback facilities. Setting up the feedback notches involves pressing and holding the switch until the number '1' shows in the little display window that's located between the switches.
As you increase the amp gain to encourage feedback, the first filter locks on, and filter two shows up in the window. When turning up the gain sets off another feedback frequency, this, too, is notched out — and similarly for notch number three. Sometimes, inverting the polarity of the signal helps to minimise the risk of feedback, and a small switch for this purpose can be found on the right‑hand edge of the case. Also on the right‑hand edge are a gain trim pot, the main input jack socket and a USB port covered by a rubber bung. Using the left footswitch normally activates or bypasses the feedback suppressor.
The display is a fairly simple numeric one, and although it would obviously have some cost implications, I'd have much preferred to see an alpha‑numeric display — one that was capable of showing the full name of the guitar Image currently running on the pedal. The same display is used for the tuner, for which a small row of LEDs at the bottom of the window acts as sharp, flat or 'just right' indicators, while the note is shown in the main part of the display. The audio output is muted when tuning, though there is a setup mode that allows you to change this if you prefer the output to remain active while tuning. A level LED on the front panel lights if the input level is set too high, and this doubles up as a battery warning indicator. It is also possible to bypass the entire unit by pressing both footswitches at the same time.
Above the switches are the three EQ knobs — each of which is centre-detented — and the single compressor-adjust knob. Finally, there are Volume (which affects both jack and XLR outputs) and Blend knobs on the top row, with the Image selector in the centre. This section comprises an eight‑position lever switch to the right of the 16‑position Image knob, the lever switch selecting a bank containing the desired instrument type (position eight is for user‑loaded images, and comes with a default set already in place) while the rotary switch selects from 16 variations on the selected theme.
You don't have to choose the Image relating to your own guitar for musical results, but to achieve reasonable accuracy you should ideally pick the correct instrument type (Jumbo, Dreadnought and so on) and then try the 16 variations to find which sounds closest. Of course, if you do stumble across a great sound by picking an image of a five‑string ukulele to go with your pre‑war Gibson archtop, there's nothing to prevent you from using it!
Turning the Blend control anti‑clockwise allows some of the unprocessed sound to be mixed in with the Aura sound, and I found that for best results it was nearly always best to use a mixture of dry and processed sound. Both the effects loop TRS jack and output jack are located on the left of the case, while the balanced XLR output is on the rear edge. Plugging into the input switches on the battery while plugging in an output jack also lifts the ground on the output XLR, so saving a switch.
By default, the low, mid, and high tone controls affect only the sound of the guitar pickup signal, not the processed signal, although a global EQ mode may be used instead, in which the same EQ settings affect both the pickup signal and the Aura‑processed signal. To select the global EQ mode, you need to hold down the tuner button while powering up, whereupon you will see the letter 'P' displayed. Pressing the anti‑feedback switch will toggle this to 'G' (for 'global').
Despite the apparently large number of controls for a stomp box, the Aura Spectrum DI is actually very easy to use, and I quickly found a couple of the 16 Dreadnought settings that sounded fine with my own Washburn acoustic guitar (even though no Washburns were listed in the image library), which is fitted with a magnetic soundhole pickup. There was a real sense of depth and body resonance to the sound, with a bright but non‑aggressive top end, and in most cases I got the best results with the Blend control set between half and two thirds up.
The feedback eliminator worked well without significantly compromising the tone, and I found that I could opt to use only one or two of the filters if that's all I felt were necessary. When playing live, though, I'd recommend that you 'ring out' the feedback during the soundcheck, as feedback can get pretty loud before it triggers the filters. Also, if you change guitar mid-performance the feedback settings will need updating accordingly. A modest amount of compression evened up the sound quite nicely, but that could, of course, provoke feedback in marginal situations. I found that the tuner had been preset to A=440Hz, and it was very straightforward to use, with more than enough accuracy to get the job done quickly.
Having tested my Washburn, I moved on to an electric guitar (a Parker Fly Deluxe) that has a piezo bridge pickup, and was able to coax some usable acoustic tones out of that. I know this isn't what the unit is intended for, though I'm sure the designers could have created a few Images to try to improve the sound of an electric guitar fitted with a piezo bridge pickup if they'd wanted to. As it was, it took some juggling with the EQ to get the zingy high end under control, and on some settings the harmonic structure was more reminiscent of a banjo, but there are some usable positions if you search for them.
Finally, I coerced one of my friends (thanks Vo!) into bringing around his collection of acoustic guitars, all fitted with piezo bridge pickups, some of which were Fishman models and some not. The notorious 'quackiness' of piezo bridge-pickups is certainly tamed to a large extent, and the results achievable using the Aura Spectrum DI are subjectively more believable than anything I've tried before. The results were, perhaps unsurprisingly, most authentic on those instruments that used Fishman's own pickup systems.
It takes some time to go through all the Images and then decide which ones works best, and you then have to find the right EQ, blend and compression settings to optimise it — which brings up the question of the lack of programmability. This isn't a problem in the studio, where you have time to make adjustments, and it's no problem live if you use the same guitar thoughout your set, but if you're one of those players who swaps guitars at regular intervals, resetting the controls could prove to be an issue.
This isn't a cheap piece of kit, and I'd still prefer to mic the acoustic guitar where possible for recording, but there are plenty of situations, both live and in the studio, where that's just not viable. If you must DI in the studio for spill‑avoidance reasons, or plan to DI your acoustic when playing live, the Aura Spectrum DI represents the state of the art in that area — and, as a happy bonus, the choice of sound Images also provides some useful alternative tonalities from the same instrument.
The only hardware alternatives I've come across are also from Fishman, but in the studio you could try your favourite 'fingerprint EQ' to see if you can get closer to the sound you want that way, or for those using a PC, you could perhaps try IJData's Bodilizer plug‑in.
- Easy to operate.
- Capable of excellent sound quality.
- Built‑in tuner, anti‑feedback system and compressor.
- Additional models can be loaded via a PC.
- No programmability.
- Displays patches by number, not by name.
This is the most effective‑sounding Aura box I've tried yet: it gives you just about everything you need to get a more natural acoustic guitar sound on stage or in the studio, although the lack of programmability may cause live players to look at other Fishman Aura units. I still prefer the sound of a properly miked acoustic, but if spill problems mean that this approach isn't viable, the Aura Spectrum can be a real life‑saver.
John Hornby Skewes +44 (0)1132 865 381.