Review: Resolution May '02
By Zenon Schoepe

SPL Kultube
Popular belief states that there has been nothing new in compression since the valve was replaced by newer circuits and then made a comeback. SPL would want to have us believe otherwise.

IT SURPRISES ME that SPL doesn’t enjoy a far more regarded position as a manufacturer. Admittedly it’s not that good at jumping on band wagons, choosing instead to go it own way and producing what some have described as ‘quirky’ boxes and others might refer to as unique. What SPL is is an ambassador and on-going evangelist for high-end analogue. Of course, it has some digital interest, like the converter option on the unit being looked at here, but the mainstay of its product development and direction is unashamed, in-your-face analogue excellence. Others may shout about it more, but SPL actually does more about it than most.

And so it is that we arrive at the Kultube, brushed finish champagne 2U that it is. First inspection may suggest yet another compressor with a valve in the line – easily spotted by the front grill positioning. Investigation reveals that it’s something substantially more. I’ve used a few dynamics boxes now and have pretty much maxed out on the hope of seeing any new spin on the business of gain reduction. The Kultube comes at it from a slightly different angle but one that the true dynamics connoisseur is likely to appreciate.
It’s a stereo compressor with a single set of controls controlling both channels simultaneously. Rear panel connectors offer balanced jacks and XLRs, a ground lift and the single side-chain access.

Described as ‘multichannel ready’, rear panel multipin connectors permit the linking of multiple Kultube’s together for multichannel compression. The master unit in the chain takes control of all the parameters on the Slave devices (units that have their Slave button depressed) with the single exception of slave units’ Tube Harmonics pots. These, incidentally, are the only pots on the front panel with a switched action so repeatability is not an issue.

Looked at on one level, all is fairly straightforward. There are pots for Threshold, Ratio (1.2:1 to 20:1), Attack (100ms to 0.9s), Release (30ms to 2s), a centre detented +/- 22dB Make Up Gain and Tube Harmonics. The last of these turns the wick up on the valve output stage progressively. It’s an arrangement that I believe is infinitely preferable to legacy valve dynamics channels that tie this effect integrally in to the compression process. The Kultube arrangement means you can get dirty with the compression part and the valve part as separate operations and that means that there are infinite variations. Things are already looking good.

It’s the row of switches above the pots that turn things around. You can switch the VU meter between input level and gain reduction and activate the digital input, if fitted. This 24/96 board has balanced XLR analogue outputs, XLR AES-EBU 1-0, and SPDIF 1-0 on phonos. A 14-position mini switch permits selection of seven modes in 16-bit or 24-bit respectively. These equate to the permutations of sampling rate and external or internal sync.

A Softknee switch softens the compression slope, Key On selects an external source coming in through the rear-panel side chain socket, while Key Listen lets you hear it. There’s a bypass button and a De-Comp switch that instigates what SPL terms ‘decompression’. Rather than causing your ears and nose to bleed, this process turns the compression process on its head to produce what others may recognise as true expansion – to effectively boost signals above threshold by an amount dialed in on the Ratio pot. The effect is particularly useful for lifting a snare or other featured percussion, but it is worth remembering that the action of the make up pot is also flipped in to reverse by the De-Comp switch. As you grab for it instinctively to turn down the inevitable increase in output, you will in fact turn it up and make things worse. A couple of really good unexpected loud blasts gets this operational twist across.

Things get clever with what SPL calls Progressive Time Control switches for attack and release constants. Don’t dismiss these as just ‘auto’ switches because while they perform this function their corresponding Attack and Release pots remain active. The former influences how much fast-rise signals are clamped down and the latter adjusts the average release time that the circuit sets back to. Regard them as user-assisted auto modes. Manual compressor setting is regularly the best solution for specific solo signals, a good auto mode can often be best for programme unless you’re working the compressor for an effect. The SPL arrangement is better still because you can ‘slide’ the constants around to give a best-of-both-worlds result.

Operationally this is a very satisfying piece of equipment. It’s not the sort of box that will spend its life wound up to full. There’s much more subtlety to it than that. You can play around with low ratios and appreciate the differences in a manner that is lost on cruder units. I like the Tube Harmonics because it’s valve-on-tap and is totally separate from the dynamics aspect, so it can be used on its own. It produces a rounded low-end lift and an authentic rise in presence, fabulous for vocals and extremely convincing on acoustic guitar even with a lackluster mic.

The stereo, rather than dual-channel, nature of the Kultube means it’s likely to be pressed in to service as a mix compressor and in honesty it won’t disappoint and the aforementioned ‘auto’ mode actually makes it excel in this area. If you can afford it, a stack of these for subgroup treatment would make your productions sound very impressive. You could even gang them together for multichannel work in what looks like a sensible and decidedly uncomplicated solution to what is becoming a real issue for an increasing number of facilities.

The digital I-O option adds sensible value with all the obvious benefit of integrating the Kultube in to digital set-ups. However, it’s still an analogue device and is the first from the company to employ discrete high-performance gain cells instead of VCAs. Sonic performance is positively exemplary, you could hang the Kultube on to anything with confidence.
So why don’t people make more of a fuss about SPL? Possibly because it continues to push the envelope and challenge the ordinary that some are clearly comfortable with. Recommended.

PROS
Exemplary performance; excellent interactive ‘auto’ mode; controllable valve character; smarter than the average compressor

CONS
Not dual channel; De-Compression mode changes pot functions dramatically for the uninitiated

Find out more about SPL Kultube