BUS-COMP Rundown: 5 / 5 Reviewer Pros - Incredibly faithful take of the "infamous" British console sound

- HPF sidechain lets you keep the low end intact

- Sonically impeccable signal path

- Built like a tank with a sound to match Cons - A wet/dry blend knob would come in handy

- Output transformers really need to be driven to hear a difference

- If you have the actual SSL, you paid $2800 too much Summary Warm Audio have carved out an impressive niche, putting world-class studio technology within the reach of producers and engineers who otherwise would only use plug-ins. A five star piece of gear if there ever was one. Rating

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British By Birth. Texas-Size Tone

Warm Audio’s latest entry in the world of analog compression takes inspiration from one of professional recording’s most famously used pieces of hardware: The stereo bus compressor from Solid State Logic’s large format consoles. Though certainly not the only high-end compressor available, it’s rightfully earned its place as many engineers’ immediate “go-to”.

Often referred to as “the glue”, this design has an almost mythical ability to put meat on the bones of even the skinniest of mixes. Elements that won’t “sit right” suddenly fold their napkins politely in their lap. Untamable Kilimanjaro-esque peaks become a bunny hill. And, for once, every member of the band stops saying they need to be louder (for an hour or two at least).

Meet The WA-Bus Compressor

That’s the sound that Austin, TX-based Warm Audio has set out to bring within reach of every even halfway-serious studio.The Warm Audio Bus Compressor is exactly what it says on the tin. Strapped across a stereo mix or subgroup, the Bus-Comp delivers a first-class, totally analog path of gluey squish, squeeze and polish. Priced at an almost-TOO-reasonable MSRP of $699, this is designed to do “that thing”… and it does the crap out of it.

Though the Bus-Comp may have some British DNA, a quick look reveals inside and out reveals as many similarities as it does differences. Housed in a sturdy black 1U steel chassis, the stereo-only unit keeps controls to just a dummy-proof set of bare necessities. Six sturdy detented knobs click in the “usual suspects” parameters – but with the addition of a selectable highpass sidechain frequency.

Wait, did you just say “sidechain frequency”?

A frequent critique of this style of compressor is the lack of an internal high-pass filter for sidechaining the detection circuit. Even SSL’s own stereo rack-mount version costing thousands more overlooks what is a very critical part of using this compressor to its fullest potential.

If you’re scratching your head at some of this, we’ll lay it out quickly (or you can check the glossary at the end): A compressor’s RMS detection circuit is triggered by the full spectrum of a mix. However, amplitude from bass-heavy instruments like kick drums, subs and low-end bass notes can force the compressor into what’s often called “pumping” or “breathing”. Cool for an occasional effect? Sure. Cool for your whole stereo mix? Probably not..

Setting a variable high-pass filter as a sidechain tells the compressor to “ignore” the rumble in the jungle below a certain point. The Bus Comp lets you dial this in all the way from 0 (off) to 185hz in roughly 30hz steps, more than enough range to find the sweet spot – letting the kicks and subs occupy their own crucial space below deck without sucking the other elements down with it.

Oh, The Iron-y

The Bus-Comp features a switchable discrete op-amp stage with two chonkin’ USA-made Cinemag iron 1:1 transformers. When engaged, the intent is to give the soundstage depth, while bringing out pleasing, subtle second- and third-order harmonics. When slapped around with too much signal activity at once, things can get wild and wooly – but not in a bad way.

This is the sort of thing that has given birth to dozens of nebulous audio industry buzz-words: “Depth”, “Warmth”, “Heat” and the dreaded “Mojo” come to mind. Warm Audio had the flash of genius to make this accessible at the push of a button, letting the user quickly decide between the two. Is it right for each application? Well, that’s why there’s an on/off button.

Warming It Up

Setting up the Warm Audio Bus Compressor is a fairly standard affair, with a beefy internal power supply fed by the included IEC cable. Inputs and outputs are available interchangeably on balanced TRS ¼” and XLR connectors, with the sidechain input on XLR only. Rack it up, plug it in, flip the switch on the front panel and the Bus-Comp is ready to go to work.

Getting your basic settings is the same here as it is with most other compressors, whether they cost half or twenty times as much. Bring your threshold down to just above where the gain reduction meter shows the compressor engaging with the attack and ratio at twelve o’ clock. Begin pulling the threshold down while simultaneously bringing the make-up gain up, keeping an eye on the meter to see just how much, and where, the Bus Comp is working. It’s important to keep switching the unit in and out to compare the compressed and uncompressed signals.

Some engineers (and I count myself among them), pull the threshold down until the circuits cry uncle and use that to dial in the attack and release times, as well as where to engage the sidechain (if at all). Then? Bring the threshold back to the land of the living and promise that you “won’t be that volume war guy”. Not today, at least.

Getting On The Bus

The other decision to be made here of course, is WHAT stereo bus is being compressed. The Bus-Comp doesn’t play favorites – and it’s just as happy to tighten the leash on your stereo mix as it is a drum bus, guitar, synths, drum overheads, room mics, vocal submixes, or any other source you desire. You could use it as a mono unit on things like bass guitar or synth – just remember that this IS a stereo only compressor without dual-mono operation.

Let’s Get This Bus Rolling

I set the Bus-Comp up as a hardware effect insert in Steinberg Cubase Pro, allowing me to quickly assign (and time-align) the unit on any stereo source in the mixer. Pulling up a mix project I’m doing for a particularly “punchy” metal-type band, I was eager to see how it performed… especially compared to similar plug-ins and hardware compressors in my rack.

Notably, the Bus-Comp was sharing space with one of my own GSSL builds using the original DBX 202 “Blackmer” VCA, as well as Cytomic’s “The Glue” and Waves’ SSL 4000 G Bus Compressor plug-ins. All close cousins of the unit being reviewed today, and all processors I am as intimately familiar with as I am the actual SSL console itself.

Observations

The very first thing I noticed is just how well the Bus-Comp exemplifies that famous, ‘grabby’ VCA sound. At lower (dare I say ‘normal’?) compression ratios and higher thresholds, the Bus-Comp efficiently and transparently tames peaks in the material while pulling up the space between the notes in a very musical, pleasing way. You won’t necessarily hear the compressor “working” with more conservative settings, but you’ll certainly miss it once it’s switched out, like getting out of a hot shower on a freezing cold morning.

I tried the Bus-Comp on a stereo pair of room mics spaced about 14 feet from the kit in a medium room that had been recorded through a pair of OktavaMod mk12’s. Instantly the room began to breathe more after every kick, hit and crash – stepping aside for the transient and falling in back on itself to give the overall kit sound some snark and presence. That’s certainly not a way you typically describe the way a metal band’s drum mix sounds in this day and age, but it was a refreshing change to hear the drums sound just a little bit more like, uh… drums.

On Drums

On the drum sub-mix, I high-passed out away the lowest registers of a particularly chesty 24″ kick drum, finally landing at 125hz, effectively splitting the drum’s effect on the compressor in half. Above that, the separation was just a little too… separate. Hearing the transients push the overheads out of the way then letting the cymbals and room wash back ashore gave the drums a huge presence in the mix – a previously unrealized bit of Bonhamesque bombast.

As an aside, while I was tweaking the Bus-Comp on the drum mix, the band’s drummer popped by to check out the progress. Seeing the new gear on top of the rack with its meter ‘thwapping’ away to the beat, he asked, “Is that what you’ve got on my kit right now?” When I replied it was and explained that I was reviewing it he asked when I had to return it, or if I could possibly keep it for long enough to finish their EP.