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Softube Bus Processor

Dynamics & Saturation Plug-in By John Walden
Published July 2023

Softube Bus Processor

As a traditional bus compressor, this plug‑in sounds great — but there’s much more to it than that!

Softube have long held an enviable reputation when it comes to modelling analogue hardware in software, so there’s always plenty of interest when they launch a new product — and that’s certainly the case with their latest release. Available in all major native formats and for Softube’s Console 1 system, Bus Processor is inspired by the SSL G‑series console’s famous compressor. And, although its primary role is to deliver that VCA compressor’s action and character, Softube have also added some thoughtful extras, including saturation and spatial processing options, making Bus Processor far more versatile than a typical ‘bus compressor’.

The main compressor controls are grouped, in a traditional SSL‑style layout, in the centre of the GUI, beneath the meter. In a vertical strip to the left of these controls, a wet/dry knob allows for simple parallel compression, and this area also hosts several more controls with which you can manipulate the side‑chain signal to refine the compressor’s response. The controls for the saturation facility sit within a similar vertical strip on the right, and the bottom strip contains the spatial processing controls, along with individual on/off buttons for each of the main processing sections, as well as a main output level knob.

As well as being fully resizeable, the GUI includes three Extended Controls panels that can be popped open using buttons located in the top‑right section of the GUI. These panels provide input and output meters (situated on the left and right of the GUI, respectively) and a further control section at the bottom. Access to the preset system and a global settings page are also available at the top.

Mission: Control

The layout of the main compressor’s threshold, make‑up gain, attack, release and ratio controls may mimic that of the original SSL, but there are some useful ‘modern’ twists too. Notably, all of these controls are continuously variable (the original hardware was limited to switched settings), and some of them offer a greater range than on the original. For example, you can set a ratio as low as 1.3:1, which is much more subtle than the original hardware’s minimum 2:1. Second, you also get a Knee option and, more interestingly, both Range and Tempo Sync facilities.

Engage Tempo Sync, and you can adjust the release knob in musical divisions (beat, bar, or percentages thereof) related to the host DAW’s tempo, rather than milliseconds. This has some useful applications, particularly on the drum bus: not only can you link the release time to the dominant beat division of the performance (quarter, eighth or 16th notes, for example) but you can more easily set up the compression to enhance the groove of the drum mix. It’s great that you can scale this setting, to fine‑tune the action to suit the source.

The extended panel for the input meters also allows you to adjust the input gain.The extended panel for the input meters also allows you to adjust the input gain.The Range control allows you to limit the maximum amount of gain reduction that will be applied, regardless of the compressor’s other settings. It’s not a unique feature but pretty rare on compressors (it’s much more common on gates and expanders), and it can guard against things getting too squashed, particularly when Bus Processor is used on the stereo mix bus.

The left‑side pane of the main GUI provides a well‑specified side‑chain processing capability, which can operate on the internal control signal or on an external key input. At the top, you can specify the degree of independence for the left and right channels: set fully clockwise (‘linked’) both channels react to a summed control signal, whereas at the opposite extreme, the left and right channels respond independently. Next, you can apply a low‑cut (high‑pass) filter, so that the compressor is increasingly less sensitive to frequencies below the chosen value. There’s also a Tone Shift control, which makes the compressor more or less sensitive to the bass or top end. Finally, there’s the option to swap the internal control signal for an external signal. So there’s considerably more flexibility here than offered by a typical side‑chain high‑pass filter!


Of course, the original SSL bus compressor offered just the main compressor control set, and with fewer available settings than here. Its real magic lay in just how well these worked in combination, and the character it imposed on the signal being processed.

Setting aside, for the moment, the additional control options in Bus Processor’s compression section, I’d say that this plug‑in is right up there with the very best emulations of this classic circuit that I’ve used. Indeed, regardless of how faithfully you believe it mimics its hardware inspiration, if you focus in on just this core control set, Bus Processor’s compressor is undeniably impressive. It works beautifully on vocals, guitars, piano and bass, for example. It’s capable of very transparent results and is very forgiving when pushed a little harder too. However, it is particularly good on a drum bus, where you can dial in all sorts of possible styles and levels of treatment. It also excels on a main stereo output bus, where, with just a dB or three of gain reduction, Bus Processor seems to help almost any mix ‘gel’ into a more coherent whole. The controls interact in a very intuitive fashion too, making it remarkably easy to arrive at the desired sweet spot.

Used like this, with the other modules bypassed, the Compressor module sounds pretty clean, though of course it does still impart a character in the sense that its dynamics processing may result in tonal changes, as the relative levels of the attack or sustain portions of a sound are adjusted. Naturally, it is possible to dial in a style of compression that’s at odds with what your project requires, but it’s actually very difficult to ‘break’ a sound, even when using fairly extreme settings. In short, Bus Processor both sounds and behaves very much like a really good hardware VCA compressor.

Saturation Point

We don’t always want ‘clean and transparent’, of course, and if you are looking to gently adjust the sonic character, Bus Processor’s Saturation module has you covered. The saturation can be placed pre‑ or post‑ the compression, and is styled on tape distortion. Usefully, you can usually use pretty much the full range of the Amount knob before things start sounding very obviously crushed, although there are some interesting results to be had by pushing the Amount control and then dialling back the saturator’s dedicated wet/dry mix.

The two Enhance buttons bring slightly different flavours to this saturation, and they can be used individually or in combination.

Softube have a well‑established reputation when it comes to modelling the behaviour of non‑linear systems and how they distort (do check out their freeware Saturation plug‑in if you’ve not done so already), and the saturation here has a very satisfyingly ‘analogue’ character. The two Enhance buttons bring slightly different flavours to this saturation, and they can be used individually or in combination. The Tone Shift control adjusts the frequency range within which the saturation is emphasised. Intuitive in use, this affords you considerable control over the contribution the saturation makes to the overall result. The Drive meter, found towards the top of the GUI, lets you visualise just how much saturation you are adding, and can be a very useful reality check. This is undoubtedly one of those addictive, ‘more is better’ effects that’s easy to overdo — as you grow used to it, you’ll tend to find that just a little of this pleasing effect can go a long way in adding body or presence to a signal.

Space For More

The Spatial module has three controls. Width adjusts the balance between the Mid (fully anticlockwise position) and Sides (fully clockwise) channels of a stereo audio signal, making the whole either narrower or wider. An Air knob boosts the high frequencies, but slightly differently in the Sides and Mid channels, to add air and sheen, while Mono Bass filters frequencies below the chosen frequency (which can be up to 500Hz) out of the Sides, so bass frequencies remain in the centre of the stereo image and the LF energy is equally distributed amongst the speakers in any playback system.

The output meter panel includes options for loudness metering, as well as the very useful Gain Difference meter and Set button.The output meter panel includes options for loudness metering, as well as the very useful Gain Difference meter and Set button.These are all very simple tools, but they can be incredibly effective, and it makes good sense to include them in a dedicated bus processing plug‑in such as this. Applied to an individual instrument bus, you can perhaps afford to be a bit more adventurous with the settings but, as with the Saturation module, a little goes a long way on your stereo mix bus. Still, it’s interesting just how much of a ‘lift’ it’s possible to give to a mix by adding just a little Air and setting the Width control in the 110‑115 percent range. As a final touch of mix (or master) sweetening to add to that provided by the compressor and saturation modules, this can be very effective indeed, though it’s important to understand, yet again, just how addictive this can be, and quickly your ears can grow accustomed to the processed sound: plenty of A/B comparisons are a good way to ensure that you avoid overcooking things.

As mentioned earlier, there are some further controls available on those three pop‑out panels, which are accessed using the buttons at the top‑right of the GUI. On the left, this gives you input meters along with an input level control. On the right, you get equivalent output metering (you already have an output level control at the bottom of the main GUI). You can configure exactly what both sets of meters display in the Settings menu. For the output meters, that includes options for peak, true peak, RMS and LUFS (Momentary, Short and Integrated, and the options to specify a loudness target). The output meter section also includes a ‘gain difference’ meter and the Set button. The former shows the perceived difference in level between the dry and processed sounds, while pressing the latter automatically adjusts the output volume to match that of the ‘before’ signal. This is really helpful, since it allows you fairly easily to assess the sonic changes Bus Processor is making to your signal, without your ears being fooled by any differences in level that result from your processing. The panel also hosts four buttons to store different configurations, allowing you to do comparisons between multiple settings of the plug‑in, should you wish.

Finally, the pop‑out bottom panel includes controls for Headroom (this adjusts the internal headroom, and reducing it allows the plug‑in to be driven harder for a given input level), High Pass (sets the frequency of a high‑pass filter on the plug‑in’s output) and Phase Invert (allows you to invert the polarity of the sound above the High Pass frequency). My own inclination was to leave this last setting well alone but if you want to explore it, the option is there!

Bus Compressor is supplied with some very useful preset starting points that you can tweak to suit your own audio signals.Bus Compressor is supplied with some very useful preset starting points that you can tweak to suit your own audio signals.

Best In The Box?

Even if you’ve never experienced a real SSL bus compressor ‘in the flesh’, you might well have encountered one of the many alternative emulations from the likes of UAD, Waves, Brainworx and, yes, SSL themselves. Having used a number of them myself, I’d say that they all have something to offer. They have plenty in common, though they do have their differences, whether in terms of the detailed character of the compression or the ‘added extras’ that each manufacturer has included. I have to say that I’d be happy to make Bus Processor my go‑to choice for classic SSL‑style bus processing.

The compressor itself sounds fabulous. It’s also very forgiving and intuitive in use and, as a consequence, it’s relatively easy to dial in different styles of compression treatments to suit your needs. The Saturation and Spatial tools are similarly easy to use, very effective and sonically seductive. So it’s hats off to Softube’s design gurus: this is a really great combination of features delivered with considerable class. It may not be the cheapest SSL compressor emulation you can buy, but it’s a brilliant one that more than justifies the asking price.


  • The compression section sounds fabulous.
  • The saturation and spatial processing are both highly addictive.
  • Well‑thought‑out feature set provides plenty of flexibility and control.


  • None, other than the temptation to overdo the saturation and spatial processing!


Although, as the name suggests, Bus Processor was conceived primarily for bus processing, it’s a powerful ‘make it better’ tool that could be used on almost any instrument or mix bus.


€149 including VAT.