You are here

Knif Soma

Analogue Mastering EQ By Eric James
Published November 2012

Knif Soma mastering EQ.

Costing almost as much as a small car, you'd expect that nothing could cut like a Knif. Find out what made our reviewer invest in a Soma...

Now, more than ever, the answer to the question "analogue or digital gear?” is not clear cut. At the lower end of the price spectrum, there are some genuine outboard bargains, but there are also plenty of boxes whose face-plates promise much, but which are left trailing in the sonic dust by (sometimes even free) software counterparts. At completely the other end of the spectrum, there's a trickle of high-end hardware processors whose price accurately reflects their inner quality — but in these instances, very positively.

It's here that we find the units that hand-made in Finland by Jonte Knif for his company Knif Audio. The company's product roster is small: there are just two compressors, a mic preamp and their latest offering, which updates and replaces an earlier model, the Soma two-channel EQ. But while Knif may not exactly be a household name, I've never read a single negative comment about their products — and their reputation as being something close to the final word in both sonic and build quality is steadily growing in mastering facilities across Europe and is beginning to take hold in the USA. With one of Jonte's devices in front of you, it is easy to understand why.


The Soma, reviewed here, is a passive EQ with tube make-up amplification. (For a quick primer on the differences between active and passive EQ designs, consult Hugh Robjohns' article in SOS July 2007: /sos/jul07/articles/qa0707_4.htm.) That's not remarkable in itself, but the devil is in the build and design details. For example, as far as I know, this is the only commercially available passive EQ that has genuine Q controls for all bands. True, there's a relatively restricted range compared with many active designs, but it means that the Soma is able, somewhat, to combine the sonic purity of passive conceptions with the more focused sound-shaping abilities of active parametric designs.

Jonte has written a detailed article on the quality factors he takes into account (as well as a few fashionable foibles which he doesn't!) when designing and sourcing components for his products. This is available in PDF format from the Soma page of his web site ( and is very well worth reading, not least for its explanation of the cost of Knif gear: "I do not use any high-end magic components, but money is spent where it really matters — and when moving from 'good' to 'the best', the price increase is very often quite painful.”

The quality is obvious straight out of the shipping box: many modern units use bent and stamped steel plates, but the Soma main case is constructed from 10mm-thick, milled-aluminium side and front plates with 4mm bottom and back plates. This has multiple benefits, from a rigidity that protects internal components to advantages for heat dissipation, grounding and protection from magnetic fields. Other quality factors can be seen from a quick peek inside: the internal construction has been designed for reliability, longevity and ease of maintenance ("a lot more work when building, less trouble in the coming years”) and all of the crucial components are of the highest spec: there are Elma rotary switches, Mundorf capacitors and Lundahl transformers. Jonte's choice of valves, the 6H30Pi (a 6922 variant) was made after extensive testing of a number of (less expensive) alternatives.

Each channel has four EQ bands: 27-470 Hz; 100Hz to 1.8kHz; 560Hz to 10kHz; and 1.5-27 kHz) plus high-pass (off/25/33/50 Hz) and low-pass (off/24/20/17 kHz) filters. The frequency within each band is selected using a 16-step switch that allows for accurate recall. Each band has a ±7dB gain control which operates in 0.5dB steps, and a Q control ranging in four steps from 0.5 to 1.5, which can also be switched from bell to shelf mode. Each band has its own on/off switch, and each channel has both an EQ on/off and a channel on/off switch. This last pair of switches probably get most use when the final feature — the in-built M/S matrix — is activated, as they let you audition the M/S signals, and EQ changes to them, separately. The M/S matrix is is passive, and it can operate on both input and output, allowing it to interface with other M/S equipment. Because of this, the channel trim control is not symmetrical: it runs from 0 to +2.75 dB in 0.25dB steps but also 0 to –6 dB, to accommodate the 6dB drop in coding if you ever want to use the Soma in stereo and then encode to M/S at the output. One final interesting feature is that in M/S mode the mid-range high-pass filter can also be switched to an 'elliptical' mode, in which the filter has a more shallow 6dB slope, and its values are much higher: 140, 200, and 280 Hz.

Transformers & Tubes

The frequency control for each band is stepped, with 16 different positions, allowing easy recall.The frequency control for each band is stepped, with 16 different positions, allowing easy recall.

For any broad design topology, there are disadvantages that will be aggravated by less than ideal design work, and advantages that may be exploited by good design. Despite the obviousness of this, it's still quite generally held that output transformers will produce a dense harmonic fuzziness, and that vacuum tube devices will sound warmer and more cuddly than their solid-state counterparts. These technical deficiencies can, of course, be put to good use in the pursuit of euphony, but the Knif Soma is an object lesson in how excellent design can virtually eliminate them if accuracy, clarity and detail are of paramount importance.

The 'transformer sound' is itself a matter of product design, and while some devices offer switched outputs, allowing you to choose whether or not to include the transformer in the signal path, the Soma does not. Why? Well, the expensive, amorphous-core Lundhal transformers (their top-of-the-range model, not the still-excellent standard series, which cost a quarter of the price) used in the Soma are probably the best and most transparent currently made. Indeed, they are so transparent that a mastering colleague of mine, having replaced the stock transformers in his main EQ (another very expensive passive design which has a switched transformer/transformerless output option), says he finds the transformer output the more detailed!

It's a similar state of affairs with valves. It should be obvious that the Miyoken-Gurevich supersonic military aircraft — better known as the MiG25 — did not employ valves because of their euphonic qualities! I've almost always used valves somewhere in my mastering monitoring chain, not because they add euphony or a nice warmth (which they certainly can do), but because in that chain, the equipment they are in does the best job.

To demonstrate just how clean the tubes in the Soma are, I decided to run some quick (admittedly non-scientific) tests for half a dozen doubting engineers who visited my Philosopher's Barn Mastering facility. I played a variety of music through the Soma, with the EQ set flat, and with nothing else in the chain. Switching it in and out of the signal path, I asked the listeners when it was in line and when in bypass. Not a single one of the engineers, not even the most hard-baked solid-stater, could reliably tell which was which. There was a difference, of course, but as often as not they guessed the difference to be the wrong way around.

In Use

Of course, the big question is what this thing is actually like to use, and the first thing that strikes you when you begin working with the Soma on a project is its exemplary ergonomics. All of the controls are nicely set out and spaced, and the switching mechanism is precise and soft.

The other analogue EQ here at PBM is the Maselec MEA-2, which is positioned early in the analogue chain and used most often to clear up the low-mids, a task at which it excels. It, too, is switched, but to change settings, the large Maselec controls have to be pretty firmly gripped and physically almost wrestled into position. That's a slight exaggeration, of course, but in contrast to the Soma controls, which can quite literally be operated with your finger-tips, that's very much how it feels. The Soma seems not only to cut or boost, but also somehow to 'massage' the sound. There are times, using a different EQ, when I find that I'd like to apply a little more boost but am prevented from doing so when sonic nasties begin to creep in — and I find myself adding, say, half a decibel but wishing it could be a little more. With the Soma, I found you could go the whole dB.

We used the Soma on a number of the projects that passed through PBM's mastering room during the review period, ranging in style from jazz-inflected songs, through indie-pop and rock, to some soft electronica. Quite by chance, the best of the projects (Kirsty Almeida's Cool Down Rewind; Rollo Armstrong's All Thieves and tracks from Dido's new album) featured characterful female vocals, and we thus discovered quite early on that equalising vocals is one of the Soma's strong points.

Perhaps the main reason for this is that the frequency region where post-mixing vocal EQ on these projects was most effective was an octave or more above the fundamental, but not quite reaching what's commonly identified as the 'presence' region around 5kHz. Working with the Soma frequencies of 2.7/3.3/3.9 kHz was often very rewarding, with just a broad 0.5-1dB on some tracks giving the vocal something extra, an upper texture, which none of the singers could positively identify (none of them said: "oh, you've made my voice brighter”) but which made all of them very happy. Many other EQs are not able to pull off this trick: boosts in that region on an otherwise well-balanced mix can quite easily cause harshness, not only with the voice but with other instruments which react badly to 3kHz boosts (electric guitars spring to mind). It isn't that the Soma is incapable of giving 'point' to the sound if that's needed — 1.2kHz on the guitars on the sides or 6.8kHz overall woke up a few mixes — but it has to be pushed harder than you'd imagine to sound anything like overdone.

Bass Desires

The rear panel is as simple as you'd expect from an all-analogue EQ!The rear panel is as simple as you'd expect from an all-analogue EQ!

At the other end of the scale, and possibly even more central to the Soma character, is its wonderful ability to shape the low end. The Soma gave excellent results when mastering the acoustic bass in Kirsty Almeida's music and on more straightforward jazz projects such as Mick Hutton's Jazz At The Movies, but I explored this aspect of its performance much further a couple of months ago when we mastered the I Like Trains new album, The Shallows.

The Soma was pretty much the only EQ we used on the entire project, and having 'opened' the top end of the sound with a simple shelving boost at 22kHz, the remaining challenge (such as it was) was to solidify the low end, keeping the weight and bringing out the texture of the bass instruments, but without any clouding of singer David Martin's unique baritone vocal style. This was mainly achieved by using the first band to boost bass frequencies (anywhere from 47Hz to 82Hz) and the next band with a gentle downward shelf from 100Hz, all in concert with the HP filter at either 25 or 30 Hz. If you can visualize the resulting EQ curves, you get the bell of the bass boost controlled at its lower end by the HP, with the downward shelf above it preventing it from adding any mud in the lower-mids. This meant that the bass boost and low shelf were working against each other to some extent, but it gave great flexibility and extremely nice textures. A related approach, which worked better in other circumstances, was to swap the order of the bell and shelf, having a low-shelf boost shaped by a bell cut around 100Hz. The resulting enhancement of the bass was pretty remarkable, so I asked Jonte Knif if he could give an explanation of it, and he just said it was down to sufficient attention being paid to coil design (they're enclosed in mu-metal and hand wound by Jonte) and the use of high-quality capacitors.

Apart from these uses in specific frequency ranges, the Soma excelled also at adjusting the overall 'tilt' of a mix: otherwise excellent mixes that were very slightly tubby could be transformed with a very broad, gentle cut in the low-mids and a corresponding lift above 2kHz, whereas slightly thin mixes could be given effective body.


The name Soma means a number of things. It literally means 'body' and is used to refer to the main part of a neuron. In the Rigveda, it is a drink that produces immortality, and in Huxley's Brave New World, it is the happy-making drug: "The soma had begun to work. Eyes shone, cheeks were flushed, the inner light of universal benevolence broke out on every face in happy, friendly smiles.” That may not quite be an accurate description of the Soma EQ in use at an attended session, but it's not all that far off! The Soma belongs to an elevated and expensive class of processors, a class costing literally twice as much as some other very good units. By the end of the review period, though, I began to think of it as anything but a luxury item: a 'luxury' to me is something that's very nice but not really necessary, whereas this is an expensive but highly desirable processor for a number of the right rational (business) reasons, ergonomic and sonic performance in particular. My business managers agreed with my assessment — so we bought one.  


If you're considering purchasing the Knif Soma, you might also want to investigate the Buzz Audio Req 2.2, Cranesong Ibis (mastering version), D.W. Fearn's VT5, the EAR 825 Q, the Fairman TMEQ, the GML 9500, and Manley's Massive Passive.


  • Superlative sound and ergonomics
  • Unique sound-shaping abilities
  • Extraordinary build quality.


  • Only the price.


The Soma is a no-expense-spared, high-end EQ suitable for mastering tasks — and it sounds as if no expense was spared as well!



Knif Audio +358 50 303 7475.


Knif Audio +358 50 303 7475.