If you are new to the technique of mix bus compression, the simple explanation is that you are compressing the entire stereo (or multichannel) mix. A compressor on the mix bus (in addition perhaps to dynamics processors on individual tracks or sub-grouped stems) can "glue" a mix together. Some engineers are fans, while others prefer to let the mastering engineer apply this global compression to a mix. 

There are many flavors of compressors for this task. Some well-known models are the Manley Variable Mu, the API 2500 [Tape Op #52], the Fairchild 670, and possibly the most widely used, the "Quad Compressor" in the center section of SSL 4000-series consoles. The SSL compressor uses VCAs to achieve dynamic control. Its sonic signature can be heard on countless records, and with good reason. It has a great way of reacting to mix elements, elbowing and nudging bits to the background and to the side as new elements enter the scene. It imparts a nice excitement to the top end, nips and tucks everything into its place, and does it all while maintaining the mix's impact. Its design has inspired several well-known VCA compressors of the same ilk, such as the Smart Research C1 [#98] and C2, low-cost options like the Chameleon Labs 7720 [#67], and of course, the rackmount and 500-series versions now made by SSL itself. 

TK Audio is a Swedish company that is marketing its BC1-S stereo bus compressor as "The Magic Glue." Indeed, the BC1-S is well suited to mix bus tasks; it's also a compressor that is capable of everything from gentle, soft-knee compression to crushing, brickwall limiting - and beyond. 

The BC1-S feels solid and has nice heft. The unit is laid out simply, with clear and well-labeled controls. The single backlit compression meter is almost identical to what you find on an SSL. All knobs are stepped or detented for easy recall, emitting a satisfying click when adjusted. Nothing feels at all cheap or compromised about this unit, and everything says "boutique" without a lot of fuss. The simple nine-page manual has great "starter" settings for different tasks, and I found it very useful for getting familiar with the piece. 

The front panel has pots for threshold and makeup gain; rotary switches for Ratio (1.5:1 to "Hard"), Attack ("Ultrafast" to 120 ms), and Release (50 ms - 1.2 sec, plus auto-release); and a Blend knob for parallel compression duties that runs from straight dry to fully wet. Accompanying the Blend control is a mute-dry button that lets you easily jump between parallel-blended and compressed-only output. A bank of three pushbuttons allows you to modify the sidechain with a high-pass filter, an external sidechain input, and an L+R sum to mono. The sidechain HPF is useful if you're trying to compress material that's bass heavy, but you don't want the bassy elements to cause the mix to pump. The external sidechain input lets you control the compressor with an alternate audio source. A noted classic example of this technique is to duck the bass track with the kick drum. With the bass feeding the compressor input and the kick drum feeding the external sidechain, every time there is a kick drum hit, the compressor nudges the bass down in level. Another familiar sidechain trick is to duck keyboard pads with the kick drum, making them pump heavily or simply breathe with the pulse of the track. Good stuff. 

Having worked a bit on an SSL console, I was immediately familiar with the sound of the BC1-S. A little goes a long way, and my love of watching a meter jump is better exercised elsewhere. I found it easy to want to lean into this unit on the mix bus, because in certain circumstances, in order to "hear" the unit, more aggressive settings were required. Be careful here. As you lean in, you start to lose your snare and other transients, and it became clear that (as noted in the manual) the meter is not quite as fast as the compressor, so using your ears is key in finding the sweet spot for your specific mix. Keeping the meter reading between 2-4 dB of reduction was typically a good bet, which kept things dynamic while they were still being nipped and tucked into place. I varied ratios between 1.5:1, 2:1, and 4:1, staying mostly with a 10 ms attack and auto-release. Worth noting is that the auto-release setting is essentially "set it and forget it," and it worked in most, if not all, mix bus situations. The image was solid and clear. At less aggressive settings, the sound was very transparent, but the compressor still managed to play Whac-A-Mole on peaks. 

Brooklyn artist Grace Weber stopped by for a couple days of tracking while on tour, which presented a great opportunity to use the BC1-S on a groove-heavy pop song or two. We were using both programmed beats as well as live drums and percussion, so transients were abound. Controlling the peaks while maintaining the energy of the track was essential. I liked what the BC1-S was doing to the drum bus with heavy-handed compression, so I printed a stereo stem of the drums using parallel blending to taste, which gave the groove a nice motion and kept the transients and punch of the drums intact. Then, re-employing the BC1-S on the mix bus, I was able to bring out great clarity and punch from the mix, without hearing unwanted compression artifacts. A great stereo bus compressor will help mix elements work together while they are corralled in a defined space, and the BC1-S delivered in spades. 

I also passed the unit over to my studio cohort Martin Feveyear for a test drive. Martin works almost exclusively on an SSL, so I valued the opinion of someone that has logged many hours with the Quad Compressor. His impression was that the BC1-S is "extremely close to the SSL," with heavier compression through it sounding a little more musical than through the SSL. He also noted that the BC1-S is very clean, with a touch more upper-midrange presence. He thought his SSL desk compressor may have the BC1-S beat by a hair in smoothness and depth. 

I personally used the BC1-S primarily on the mix bus, typically A/B'ing and printing mixes with it and my Manley Variable Mu. I produce and mix in a variety of styles, so having the BC1-S on hand as one of several options was a huge benefit. On a couple occasions, I used the BC1-S for compression duties while following it with the Variable Mu for limiting. This was really the best of both worlds for me - marrying the punch of the BC1-S to the warmth of the Manley. 

For other compression duties, the BC1-S performed admirably. It was nicely aggressive on bass, as well as solid and transparent reining in vocal peaks and sticking a guitar solo in place. It was hard to find anything on which I felt this compressor was an absolute-no. 

We all have our favorite pieces of gear, and this quickly became one of mine. It can operate invisibly as a utility, or it can add character when I want to dig in a bit. Once you know that this particular flavor is available, you will want to return to it frequently. There are times when this sound is exactly what an individual element or a whole mix needs to bring it home. Anyone looking for a fantastic and reasonably affordable version of the classic SSL VCA compressor cannot go wrong with the TK Audio BC1-S.

$1349 street; www.tkaudio.se
Geoff Stanfield is at geoffstanfield.com

Tape Op is a bi-monthly magazine devoted to the art of record making.

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