PSP auralComp

Intuitive and powerful, this compressor can handle anything from mono up to 7.1.4 Atmos sources.

auralComp isn’t PSP Audioware’s first plug‑in to support Atmos — that honour goes to auralControl, which was released last year and enables you to rebalance the levels in multi‑channel tracks — but PSP made their name with some great‑sounding effects and processors for music, and this is their first signal processor intended for immersive audio.

As a multi‑channel compressor and brickwall limiter, auralComp is a broadly similar sort of tool to Waves Spherix, which I reviewed back in SOS February 2023. But a key difference, and an improvement in my opinion, is that auralComp isn’t limited to use with 7.1.2 or 7.1.4 channel widths: you can use it on mono, stereo sources (and can process stereo in M‑S), quad, 5.0... in fact, any number of channels, all the way up to 7.1.4. auralComp supports the AAX, VST3 and AU plug‑in formats for DAWs running on macOS or Windows, and can be authorised on up to three (of the licence holder’s) computers.

Overview

To develop auralComp, PSP partnered with Dutch engineer and producer Ronald Prent, who is known for his work with Simple Minds, Depeche Mode, Def Leppard, Tina Turner, Rammstein and the Scorpions, and many more. Ronald has specialised in surround sound mixing since the early ’00s, at which time he helped with the development and testing for Sony’s SACD format and worked with API to create a multi‑channel version of their 2500 compressor. With the recent boom in immersive audio production in mind, he reached out to PSP to see if they’d be interested in developing a plug‑in built around the same concepts, but taking the ideas further where digital technology allows. (Having said that, I should make clear that this is not a model of API’s compressor!)

The channel grouping facilities make working with multi channel formats quick and easy.On opening the plug‑in, each channel’s compressor is displayed in a separate ‘strip’ and, as you can see on the main screenshot, the user‑adjustable parameters are the sort of thing you’d expect to find on any compressor, with knobs for attack (0.1ms to 160ms), release (25ms to 2500ms), threshold (‑40dB to +10dB), make‑up gain (variable up to +20dB), ratio (1:1 to infinity:1), and wet/dry mix. There’s also a group of three LED‑style bar meters. These indicate the input and output levels and, in between, the amount of gain reduction being applied. There’s no labelling or current/maximum readout to confirm what’s going on, which seems an oversight — uncertain about what value each LED segment represented, I sometimes found it tricky to tell exactly how much gain reduction was being applied. Having said that, the layout makes it easy to match the output level to the input level, and the make‑up gain you apply to do that gives you some sort of indication of the gain reduction taking place.

On the right‑hand side is a ‘quick select’ control section that makes it super simple to dial in the desired amount of compression on whichever channels you wish to process. Channels can be grouped so that, for example, you can adjust the threshold of all three front channels simultaneously, while leaving the thresholds of the other channels alone. The available groups are All, Fronts, Sides, Rears and Tops, and because each group is colour‑coded it’s always clear what you’re about to change when you grab a control. At the bottom of each strip is the option to switch the compressor in/out for that channel.

Chain Gang

Some might find the compressor’s side‑chain ‘circuit’ fairly complicated, but it’s useful and extremely well thought out, and the possibilities are myriad. There’s the link control on each channel, perhaps inspired by Prent’s experience with the API 2500, and when this is set to zero percent, the compressor reacts only to the channel’s own input signal. As you turn the knob towards 100 it becomes increasingly sensitive to the selected side‑chain signal, which is where things start to get interesting... Each channel’s side‑chain can be your choice of eight submixes of all the channels. By default, these are called Alpha, Beta... and so on up to Theta, but they can be renamed. You select the desired submix at the bottom of the strip, and below that is a helpful side‑chain display window, which shows you a visual representation of the level of each channel in the submix, and how it corresponds to the actual side‑chain level triggering the compression.

auralComp boasts a sophisticated internal side‑chain routing system that allows any channel or group to respond to a custom mix of the other channels.

Importantly, you can tweak the side‑chain submixes: clicking in the top right of the side‑chain display window opens up a submixer with which you can adjust the levels in each submix — this can be done very quickly thanks to the quick select group controls I mentioned above. There are also a few filters available. Options are an HPF, adjustable from 20Hz to 20kHz; a band‑pass filter, again adjustable from 20Hz to 20kHz and with an adjustable Q (0.01 to 10); an Equal Power filter (a curve designed by PSP that they say is intended to equalise energy across the entire spectrum); and a 20Hz to 20kHz LPF.

The final thing to mention about the compressor is the side‑chain summing option, which applies to all the side‑chain submixes. There are three choices: Natural is a conventionally summed submix, while Rectified rectifies the audio signal before summing, and when RMS is selected an averaged signal is used to trigger compression. PSP tell me that there are no rules — that the best choice is really a matter of taste — but Ronald Prent finds that RMS works well for him on classical recordings and normally prefers Rectified when working with rock. Personally I usually tended to prefer the Natural setting, but I’m sure plenty of people will find this subtle option for shaping how the compressor reacts to the audio signal useful.

I even found myself wishing I’d had access to this plug‑in a couple of weeks earlier, for a project I’d recently finished.

In use, I found auralComp’s compressor to sound big, warm, and open. On the main Dolby Atmos 7.1.2 bed for the project I was working on at the time, a little gentle compression really helped to ‘finish off’ the mix — and I even found myself wishing I’d had access to this plug‑in a couple of weeks earlier, for a project I’d recently finished. It was also easy to ‘crunch up’ multi‑channel drum busses and then use the mix control to dial in the amount of compression to taste. It can go from gentle to punchy, to crunchy. In the manual, PSP suggest that “scenarios like ‘rears are listening only to the fronts, sides are listening partially to the centre channel, ceilings are listening to the high‑end information of all channels, and the LFE is excluded’ are very simple to set up.” I couldn’t agree more: the degree of control offered in the side‑chain section really does give you endless possibilities. Being very picky, I’d love to have an external side‑chain option too, so that other instances of auralComp could be applied across individual objects and multi‑channel busses and be keyed from the same source material. Perhaps that’s something to consider for a future update.

On The Level

To the right of the compressor channels is another strip, which hosts global ±10dB input and output level controls and, tucked in between these, a switchable brickwall limiter that works independently of the compressor side‑chain options. There’s nothing fancy in terms of control here, but that’s all right by me. Basically, you set the desired ceiling level (‑20 to 0 dBFS) and the signal never exceeds that on any channel. If you want things louder, turn up and hit the limiter harder. There’s also a Drive control, adjustable from 0 to +20 dB. As a visual indication of where you’ve set the ceiling, a helpful blue line appears on all the channels’ output LED strips. To my ears, the limiter sounds really smooth, and can be pushed pretty hard if desired. I found across my Atmos bed I could crank the Drive and hear the mix starting to change, with the ambience and reverb in the rear channels coming up in volume, long before my ears could detect any undesirable artefacts.

My overall feeling? I love this plug‑in — from now on, it will definitely be a staple on my Dolby Atmos mix sessions. My biggest gripe is with the metering (more information would be welcome) but that wouldn’t stop me using it, and who knows, maybe that can be improved in future versions. External side‑chain support would be another welcome addition. But it would be unfair to focus on what this plug‑in doesn’t do, because what it does do, it does it very well indeed. auralComp’s compressor is very pleasing to the ear and very quick to set up, and the limiter super‑easy to use and transparent sounding. Being able to use this processor on a variety of channel widths is a real plus, too, because not every mix will be an Atmos one. PSP offer a free 30‑day trial, and if you’re working in immersive audio I’d say that this is definitely a plug‑in you should take for a spin.