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Demeter RV1

Dual Spring Reverb
By Paul White

A high-spec spring reverb for the digital age.

Demeter RV1Photo: Mark Ewing

While most of today's reverb comes from digital processors rather than echo rooms, plates or springs, there's no denying that the old analogue systems have a character that digital systems find very hard to duplicate. Perhaps the magical warmth is down to the infinitely dense reverb field created by physical systems — most digital reverb units start by generating individual reflections. For example, if a spherical sound wavefront hits a flat wall, you don't just get one reflection, but an infinite series of them as the various parts of the curved front reach the wall. These scatter off in all directions and this reflected energy behaves similarly when it encounters other surfaces, building up into a complex sound energy field where the concept of individual repeats or reflections becomes irrelevant. The word 'homogenous' perhaps best describes natural reverb, and while plates and springs aren't direct counterparts to what happens in nature, they do share that homogenous characteristic.

Plates are large, expensive to build and have to be isolated from noise, which means they're less than ideally suited to project studio use. Springs are less costly and far more compact, but they've attracted a lot of bad press over the years because they are often noisy and have a tendency to sound fluttery. While springs work well with electric guitar, relatively few serious studio spring systems were ever built. Now James Demeter believes he's cracked the most serious technical problems and, in the process, designed a good-sounding spring reverb unit that deserves a place in the modern studio.

RV1 Real Reverb

Housed in a 1U rack, the Demeter RV1 Real Reverb is based around two long Accutronics spring 'tanks', each of which contains three springs (actually six strung together to form three long springs). The receiver end of each tank is shielded with mu-metal foil to reduce interference from magnetic fields, though it is still important to mount the unit away from strong magnetic fields to ensure hum-free operation, as the coils of the pickup transducers are quite sensitive. One spring tank has a 1.5-second decay time, while the other has a 3.5-second decay time.

Demeter RV1 £699
pros
  • Low noise and minimal flutter.
  • Can be used in stereo or dual-mono configurations.
cons
  • The decay time is fixed.
  • In stereo mode the left and right decay times are different.
  • Not cheap!
summary
This is one of the best-sounding spring units I've tried and should appeal to anyone interested in a more retro sound. However, it seems expensive when compared with multi-functional digital units.

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Part of the problem with spring systems is getting anything like a flat frequency response out of them, but the circuit design used here helps the transducers operate more consistently over the frequency range, both at the drive and pickup ends of the spring. The audio ins and outs to the unit are also fully balanced (on both jacks and XLRs) using Analog Devices 2142 and 2143 amplifier chips, while the power supply operates at 18V to provide plenty of headroom. A toroidal transformer is used in the PSU circuit along with a couple of standard regulator chips, and all the circuitry (which is chip-based) is mounted on a narrow PCB at the front of the unit. The cables leading to the rear panel are clipped down to prevent contact with the spring tanks and some kind of mastic is used where the tanks sit in their suspension cradles to prevent the suspension springs from becoming dislodged.

Each spring has its own set of controls and can be used independently as a mono-in/mono-out reverb processor, but there are also separate link switches for the inputs and outputs so that the unit can work as mono-in/stereo-out or mono-in/summed mono-out. Two of the three rotary controls are to do with level, the Input control being used to set the optimum audio level feeding the springs. An overload indicator turns red if the input gain is too high. The other level-related control is Output, which simply sets the level feeding the next device in line. The Mix knob balances the relative levels of reverb and dry signal, though this would normally be left set fully clockwise when used in an effects send loop.

In addition to these three simple rotary controls are two switches, one for phase and one to introduce a low-cut filter into the reverb path, the latter to remove muddying low frequencies when treating sources that have a lot of low end. Phase can be used to put one reverb spring tank out of phase with the other, which provides a slightly different tonality, and because the outputs from the two springs aren't correlated in any significant way, there's no obvious comb filtering or heavy cancellation of specific frequencies. The effect is also slightly different if you flip both phase switches, as the way in which the wet and dry elements combine changes slightly, adding a bright shimmer to the sound.

Testing Time

I tested the Real Reverb using a number of instrument sound sources as well as vocals, and found that, provided that it was mixed at a sensible level relative to the dry sound, it produced a warm and musically satisfying reverb. Because the spring tanks have different decay times, using the unit in stereo-out mode results in a faster decay time on one side than on the other — although this is not musically unpleasant, it's not really what you expect to hear. Unlike digital reverb units that invariably start off with a series of artificially generated discrete early reflections, springs feature a very fast build-up of density with no noticeable early reflections to speak of. The result isn't quite like a real space, but it is musically sympathetic in the same way that plate reverb is. If you listen to the reverb signal in isolation, it sounds somewhat less impressive, and although the flutter element that's common to all spring reverbs has been tamed pretty well, it's still there if you feed in a percussive sound of any kind. Nevertheless, once the dry signal is added, the imperfections seem to dissolve, leaving a warm, smooth reverb decay. You can even use the Real Reverb with drums, though you have to keep the reverb level fairly low to avoid giving the game away.

The RV1's reverb is generated by the two long spring tanks which you can see here running across the entire width of the rack unit.The RV1's reverb is generated by the two long spring tanks which you can see here running across the entire width of the rack unit.Photo: Mark Ewing

The electrical noise from the unit is surprisingly low from a spring device, provided that you set the input gain as high as you can without getting the overload light to flash, and though you do get the familiar 'thwaaang' noise if you knock the unit, it's well enough behaved once mounted in a solid rack.

Interestingly, the Real Reverb works quite well in conjunction with simpler reverb plug-ins, most of which are sadly lacking in density when used on their own. If you feed the reverb signal out through the Real Reverb, the missing density is replaced, but you still retain some of the character of the early reflections. If you want a longer reverb time, you can use the digital reverb unit to create the length you need, then use the Demeter Real Reverb to add density and mellowness.

Puts A Spring In Your Step?

Given that good digital reverb units can be bought relatively cheaply, the Real Reverb may seem quite expensive in the UK, but it does offer an alternative reverberation character that some people may prefer in specific situations, not least for electric guitar or vocals. It will be of particular interest to anyone seeking to create an authentic retro sound, and though there are cheaper spring units, this is the best-behaved one I've tried to date. Given that a good digital reverb unit will satisfy most of the people most of the time, I can't put my hand on my heart and say the Demeter Real Reverb is a 'must have' effects unit, especially given the inflexible nature of springs insomuch as their decay times are fixed, but it does offer a musically attractive alternative that works well on its own or in conjunction with digital reverb.

information
infop.gif £699 including VAT.
infot.gif Audio Agency +44 (0)1908 510123.
infow.gifwww.audioagency.co.uk
infow.gifwww.demeteramps.com
Published July 2003