Exploring the SSL THE BUS+ Stereo Bus Compressor

The SSL 4000 G console’s stereo bus compressor is one of the most beloved audio processors of all time. Providing fast-reacting VCA compression with a simple set of controls, the “G Bus,” as its fans call it, seems to enhance anything that goes through it, making mixes sound like more than the sum of their parts.

Solid State Logic’s THE BUS+ features the same legendary compression circuit at its core, repackaged into a rack unit and augmented with multiple compression modes that provide different sonic “flavors,” a new 4K Mode with nine levels of harmonic distortion, dynamic EQ, flexible sidechain options, and the ability to rearrange the internal signal chain. 

This versatile unit has so much to offer that we couldn’t cover it all in a video and a blog, so we sat down with Vintage King Audio Consultant Anthony Vaticalos to dig into everything THE BUS+ can do—and how to get the most out of it in the studio.

While its main role is mix bus processing, The Bus+ has some features that mastering engineers can appreciate as well. Who is this really for? 

Anthony Vaticalos (AV): The top use case would be getting that punchy VCA-type compression on the whole mix. It does a great job of doing what most people experience with SSL bus compression, but it’s packed with so many more different options, features, and ways to get creative; like the dynamic EQ, different compression modes, and the fact that you can split it up into dual-mono. As far as its historical application, most people are familiar with the SSL bus compressor for mixing, but I think this unit could land in a mastering engineer's setup because of the mid-side feature, the dynamic EQ, and all of the different options for shaping tone.

Tell me about the different compression settings. What effect do the Low THD, Feed-Back, and 4K modes have?

AV: The Low THD and 4K modes affect the headroom to distortion, and the Feed-Back mode is just going to affect which stage the compressor reacts at. Low THD mode lowers the total harmonic distortion by reacting differently to low-end information. It gives you more headroom, essentially. 4K mode is kind of the opposite—it will reduce your headroom and add all this grit and harmonic character to it. There are nine different stages, with one being the most subtle and nine being the most aggressive and grungy, and it’s also reactive depending on input level. The whole point of mixing on an SSL is to push it. And when you push it, you start getting those harmonic characteristics, especially with the bus compressor in the center section. So what they did here was just give you a boatload of options to add character.

Feed-Back and Feed-Forward refer to where in the circuit the sidechain signal comes from: before or after the compression stage. Feed-Forward is the default, and that's your quick, punchy VCA compression, while Feed-Back is a little bit more relaxed and transparent.

From THE BUS+ manual:

“Although the Bus Compressor side-chain per se has a 'feed-back' topology, the signal feeding

the side-chain is derived from a feed-forward position. Engaging the F/B switch derives the

signal feeding the side-chain from a feed-back position (i.e. after the main gain-reduction

VCA in the audio path). This results in a more 'relaxed' style of compression, in contrast to the

traditional 'grab' of the Bus Compressor.”

The Stereo, Dual-Mono, and Mid/Side modes will be familiar to most engineers, but the Sigma Sidechain Stereo mode is rather unusual. What does it do and what is it useful for?

AV: Internally, it's creating a sidechain signal by summing the stereo input to mono, which affects the elements in the middle differently. The output is still stereo, but in my experience, it gives everything in the middle a little bit more presence. It can be a subtle effect, but on a drum bus you can really hear the difference with the kick and snare, which will fill in the center a little bit more, as opposed to just being ducked with standard stereo compression.

Dynamic EQ is a feature you don’t often see in rack units like this. How is it implemented, and what are some ways to use it effectively?

AV: It’s a really great tool, and it can do either compression or expansion. If the low and high-frequency knobs are at noon, going to the left is going to compress, and going to the right is going to expand. You can also go into a fine control mode, which changes the increments from one decibel to half a decibel. In the video I did, I was expanding a little bit on the higher frequencies and ducking the low end around 60 Hz too, because it was a kind of dark mix.

You can even move all the different elements in different orders, so you can do your compression pre- or post-dynamic EQ so the compression reacts before or after what you're doing with those EQ points. The external sidechain can also go before or after both the compressor and the dynamic EQ. The routing is crazy, it's full of options!

Starter Settings

Rhythmic Pop/Rock Mix

“I'd probably start in basic Stereo mode with the threshold dependent on how hot the track is. For the attack, I usually start at 30 milliseconds, but if it's got a pretty heavy kick, I might do 15 to 20 milliseconds on the attack. I’d probably want it to release pretty quickly to give it a little bit more of an aggressive feel. Ratio might be around four at the most. Mix all the way up. I’d probably set the sidechain filter to 50 or 60 depending on where that kick is.”

Dynamic Ballad Mix

“I'd go with Feed-Back style compression, with the ratio maybe at two. If it's a ballad, it's probably going to be pretty dynamic, and I don't want to crush anything. I might do some expansion on the high-end just to get a little bit more brightness out of it and see how that would react. I might try the Sigma Sidechain mode because there may be be a lot of energy in the center.”

Aggressive Drum Bus

“I'd use 4K mode, maybe halfway because I want to get some more grit. Threshold's probably going to be pretty low so I can get more squeeze out of it. Anywhere between a four and five on the ratio, or I might select a negative ratio for this to add more excitement to what's going on. Release would depend on what the pumping feels like, but generally not too fast. Mix all the way up."

Dual Mono: Bass and Kick Drum

For bass guitar, I would go for a slower attack to let those notes come through. Low ratio and a medium release time because I probably want to create more sustain. I might do some dynamic expansion depending on what the arrangement of the song is in the low end. For the kick drum, if it’s a round, pillowy kick, I would probably set the attack around 15 milliseconds with a fast or medium release depending on how big the transient is. Ratio would probably be around four, in feed-forward mode with Low THD engaged.

Final thoughts

If you’re craving that classic SSL bus compression but need a lot of tonal flexibility, THE BUS+ is a solid addition to your mixing or mastering setup. Take Anthony’s word for it: “This thing is a freaking workhorse,” he says. “I'm still learning it after playing with it for a handful of months now.”

If you’re near Nashville or Los Angeles, stop into a Vintage King Showroom and set up an appointment to try out THE BUS+ for yourself!

If you have any questions about the Solid State Logic BUS+ or would like to purchase one, we're here to help! Please contact a Vintage King Audio Consultant via email or by phone at 866.644.0160.