Let's Discuss the Knif Soma Mastering Equalizer
Body of Sound. Jonte Knif’s Soma and Chris Henderson’s Michelangelo form the tube EQ suite on our desk.
Readers of our Vari Mu II discussion will already be familiar with our mild obsession with Knif Audio and with Jonte Knif, who has been designing and hand-building audio equipment in Helsinki since 2005. We briefly mentioned two of his designs, Soma and Eksa, as two of the most transparent, accurate, and musical equalizers ever conceived. Soma, Jonte says, is designed with careful consideration for "the beauty of sound." I can confirm that this is not marketing language.
Etymological note: "soma" in Finnish can mean something like "pretty". In Ancient Greek "soma" means "body". In Vedic Sanskrit, "soma" can refer to a psychedelic cocktail made from psychoactive botanicals.
Soma is a dual-channel passive tube equalizer intended for mastering. That description suggests it ought to be categorized alongside the Manley Massive Passive or a pair of switched Pultecs. If that were the whole story, Soma would still be a very fine equalizer. However, Soma gracefully departs from the passive EQ tradition in one respect: it is the only commercially available passive EQ with real bandwidth adjustment. On a conventional passive equalizer, changing the bandwidth parameter will inadvertently alter the amount of boost or cut being applied, leading to unexpected shifts in the resulting EQ curve. Engineers have accepted this compromise for decades. Jonte did not. On Soma, when one adjusts bandwidth, that is the only parameter that changes allowing one to dial in gain at a specific frequency and then widen or narrow the curve without disturbing the amplitude. In practice, this yields dramatically finer control over the transfer curve than any other passive topology. One can sweep with a tight Q, find the right spectral region, and widen the curve — the same methodology one would use on any parametric — except here, with all the benefits of induction.
The engineering that makes real Q adjustment possible? Jonte and his gnomes wind the inductors with the maximum number of taps required to switch between enough inductance and capacitance combinations to change bandwidth without altering gain. Fewer taps would mean coarser steps, or the kind of Q-gain interaction for which every other passive EQ settles. The makeup gain amplifier is a simple two-stage tube affair paired with Lundahl amorphous core output transformers. Together, they introduce a controlled, subtle beautification of the signal. When pushed hard, there is a saturation afforded by Soma which is not harsh, gritty, or conversely flabby or farty. It's simply a smooth sausaging of the input signal.
On the faceplate, one will find what appears to be a small city of Elma rotary switches. All of them are fitted with soft touch collet knobs that propel the unit squarely into luxury territory. Every setting is stepped, every setting is perfectly recallable. I can't overstate the value of switches over continuously variable potentiometers in a mastering context. Soma offers four bands of parametric equalization with interleaved frequency ranges from 27 Hz all the way up to 27 kHz. Each band can operate as a bell (0.5, 0.7, 1.0, 1.5) or be switched to a shelf, and each has its own bypass. Boost and cut range is ±8 dB across all bands. Trim controls, high-pass, and low-pass filters round out each channel's controls.
Soma's M/S encoding and decoding is performed entirely by multiple windings on the input and output transformers, switched locally with relays. This means engaging the M/S matrix does not add any components to the signal path. Mid/side processing often introduces compromises, but Soma's implementation is as sonically invisible as materials science allows. The unit can also function independently as an M/S encoder or decoder for subsequent stereo units in the analog chain, just like Vari Mu II's independent M/S switching. In M/S mode, the side channel's high-pass filter can be switched to a gentler slope with significantly higher frequency selections, enabling elliptic filtering and effectively narrowing the stereo image in the low frequencies, concentrating bass energy toward the center. Vinyl mastering folks may appreciate this, but its utility extends beyond the lathe, allowing one to centerize bass or de-mud the side channel in a variety of circumstances.
Thoughtful Asymmetry. The channel trim control runs from 0 to +2.75 dB in 0.25 dB increments on the boost side, but extends just past -6 dB on the cut side.
It should be noted that Soma can do things that others struggle to deliver. One can go further with boosts in the bass or treble regions that typically get boomy or harsh, respectively. Similarly, one can cut more recklessly where there is especially loud bass, midrange, or treble information without losing the essence of the program material. Perhaps the one drawback is that Soma's transparent nature does not encourage one to "paint with colors" in the way that other passive EQs do, but it excels most when it is used for exactly that. It is musically transparent. So, Soma keeps me listening to the song, not Soma!
Despite the breadth of possibilities offered by this exceptionally engineered box, the most common way I employ Soma is by keeping all EQ parameters at unity (save for filters, perhaps) while feeding the unit the right amount of gain to get that “subtle beautification” that Soma so easily provides.
That means on my desk, Soma is most often a tone box, and it isn't even applying "real" EQ. Used in concert with Vari Mu II, the subtle enhancing effect that comes from each of these Knif processors is just superb.
Knifaudio.com
P.S. Plugin Alliance has released a plugin version of the Soma in collaboration with Brainworx. It is a usable digital interpretation that I own, but admittedly rarely use. The interplay between Soma and Vari Mu II is what makes Soma so special. Notable users of Soma include, unsurprisingly, Mike Kalajian of Rogue Planet Mastering, Brock McFarlane of CPS Mastering, John Greenham of Clearlight Mastering, and many many others.