Let's Discuss the Knif Vari Mu II Mastering Compressor
A Gentle Reaper. The Knif Vari Mu II in its industrious glory boasting unparalleled analog transparency combined with the promise of righteous saturation.
Knif Audio was founded in 2005 in Helsinki, Finland. Over the past fifteen years, Jonte Knif has designed and hand-built audio equipment that is held in the highest regard within the audio community. For example, the Soma and Eksa are revered as two of the most transparent, accurate, and musical equalizers ever conceived. The Soma excels at enhancing program content with careful consideration for “the beauty of sound”, while the Eksa (“exact”) grants unrelenting precision and an even smaller sonic footprint.
In the realm of compressors, Jonte has crafted a Vari Mu series that boasts the same transparency offered by the Soma and Eksa. The Vari Mu II is the flagship unit, whereas the Pure Mu is its “little brother”. The unit we have here at Rose Quartz is the flagship Vari Mu II model, without the optional Lundahl amorphous core output transformers.
Total transparency: In the time following the release of this article, we have since replaced the mu metal transformers with Lundahl amorphous core transformers — a simple (and somewhat expensive) modification.
Upon racking the unit, which is no easy task as the box is 4 units high and quite heavy, it is evident that Knif Audio gives the structure surrounding their monstrous electronics the care and attention that it deserves. The metalwork in particular stands out; NASA may be interested in the companyʼs manufacturing methods, as the Vari Mu II most likely could survive re-entry into Earthʼs atmosphere.
Inside the box, the Knif Vari Mu II sports 10 tubes: 4 ECC189 compression tubes, 2 ECC88 and 2 6H30Pi output amplifier tubes, and 2 6AL5 sidechain rectifier tubes. Furthering the Vari Mu II’s quest to reach critical mass are Lundahl’s oversized transformers. Together, they provide transparent, musical saturation to program content when the unit is suitably driven.
Playing God. With twenty-one switches onboard, the Vari Mu II allows for an immense amount of control over a source signal’s dynamics profile.
On the faceplate, one will find what appears to be many knobs. However, these arenʼt knobs at all — theyʼre a total of 15 Elma rotary switches. One might wonder, why so many switches? The simple answer is that the compressor sports more than enough features to justify the cluster of controls.
The left side of the unit is the gain section. Here, one can find input and output controls, a bypass switch, and dedicated switches for both input and output mid/side encoding. This means that the unit can function independently in mid/side mode, and can effectively grant subsequent stereo units in the analog chain mid/side capabilities as well. Countless possibilities immediately come to mind without any mention of a mastering controller or transfer console; turning an off-the-shelf stereo equalizer into a mid/side equalizer, for example.
Moving on to the central section of the faceplate, one will find the usual compression control suspects — threshold, attack, release, and ratio. The ratio switches are marked from 1 to 6, which correspond to compression ratios ranging from 1.5:1 at position 1 to about 10:1 at position 6. The ratio control also has an “off” position. Using the 1.5:1 position in conjunction with an appropriate time constant allows for the most gentle, transparent compression imaginable both for macrodynamic and microdynamic applications. For the time-based controls, release times range from 33ms at position 1 all the way to 1500ms at position 11. Attack however is proportional to primary release, varying from 50% of release time at the slowest to “breakneck” at the fastest. This is because each position on the attack switch is 2x faster than the previous setting. Therefore, with a release time of 33 milliseconds, one could achieve an attack time of 16.11 microseconds, or just under ⅕ of a millisecond, which encroaches upon FET circuit territory. Whether youʼre looking for big-picture macrodynamic nudges in the right direction or near physics-defying microdynamic control, the Vari Mu is up to the task.
In addition to the standard compression controls, the unit has dedicated dual release switches for both the L/M and R/S channels. Each switch has three positions: off, 1, and 2. The two different dual release modes are based on optical-style memory effects and various release modes from the legendary Fairchild 660/670. Jonte calls the dual release feature something like a primitive volume automation. The way I would best describe it in use is by saying that by using dual release modes, an engineer can have the gluey qualities of a vintage Fairchild at quite literally the flip of a switch.
In technical terms, the dual release allows for a secondary slope to be applied to a faster primary release time, nominally 1 or 2 seconds. The secondary release is engaged more aggressively when relatively more gain reduction has been applied prior to primary release.
In addition to the compression controls, the central section houses a sidechain high-pass filter with 3 frequency selections: 20, 70, and 150. Worry not, though — even set to 20 Hz, the Vari Mu has plenty of headroom for bass and protects the low-end from distortion. Moving along, we see a switch for R/S trim that ranges from -2.5 to +2.5 in 0.5dB increments, allowing for precise stereo image control and mid/side balance.
Perhaps the most curious control on the faceplate is the 5-position channel Link control. Positions include “Off”, 2, 3, 4, and “On”. Positions 2, 3, and 4 allow for partial channel linkage based on time-dependent performances on each channel. For example, a jazz recording, or perhaps an ultra-modern future bass track, may have far-panned transients or large-scale lateral dynamic shifts that could yield unfavorable results in terms of stereo transient response while applying compression in full linkage. However, utilizing one of the partial linkage modes will allow for some dominion over lateral transient-response without compromising linked makeup gain. I would imagine that this function would be immensely useful for the two real-world examples previously mentioned. Admittedly though, I haven’t found many everyday uses for this feature in practical applications.
According to Jonte, attack periods will be linked less than release periods while operating in partial linkage modes. One can achieve interesting results with partial linkage modes if the program material allows it.
Dual, illuminated Sifam meters jump up to -3 a few seconds after powering on, slowly creeping up over the next few minutes to rest at 0. If the needles are unsure about where theyʼd like to settle, calibration is made incredibly easy with front-panel access to tube balance and meter zeroing controls. This unit does have a considerable warm-up period, after which time it is truly warm — the faceplate can be quite hot to the touch. According to the manual, the unit’s sound stabilizes after it has been powered on for about 15 minutes, after which time the sound quality will not change noticeably. The key there is the word noticeably. There is very little that is noticeable about the unit, unless a noticeable effect is desired. In standard operation, this unit is as transparent as a freshly cleaned corporate glass-walled conference room. But given the right input levels and compression settings, the Vari Mu II can provide an enhancing drive to program material.
It is exceedingly difficult to describe the way that this compressor has made its way into my everyday workflow. This unit excels at solving problems in the often controversial world of dynamics. Every time I engage the compressor, I find myself using it in a solution-oriented, purpose-driven fashion that is specific to the program material. Some tracks that need “oomph” or “glue” get classic Fairchild or optical-style compression using a 1.5:1 ratio and the dual release switches engaged to a preferred setting, yielding .5 to 1.5dB of gain reduction. Other tracks get no gain reduction at all and are simply fed into the compressor at a high level to receive the subtle enhancing qualities of the Input and Output sections. Sometimes the mid/side encoding can be especially useful for mono transient control or stereo imaging. The unit also functions very well as a clean transparent mastering compressor, remaining transparent with the right settings up until 4 to 5 dB of reduction. That kind of transparency with a tube compression unit is profoundly remarkable.
Overall, it’s quite a challenge to make this unit sound bad. I wish I could say that I have a starting point in terms of my preferred settings with this unit, but this compressorʼs strengths are so heavily dependent upon program content. This is largely a positive point as it keeps me as a mastering engineer song-oriented. Oh, and it makes my job just that much more fun; I end up turning knobs like Iʼm 15 again, tweaking the settings on my Twin Reverb.
Knifaudio.com
€5200 (about $6200 given current exchange rates)
P.S. This unit has something of a cult following. Notable users include Chartmakers, CPS Mastering, and Rogue Planet Mastering. Mike Kalajian from Rogue Planet is actually the person who suggested that we purchase the unit.