Cytomic have gone to great lengths to mimic the sound of the famous SSL bus compressor, with its unique ability to 'glue' things together. How does their plug‑in compare with established offerings from Waves and UA?
Cytomic are a rather new company, but do not lack in experience when it comes to making plug‑ins. The CEO and founder Andrew Simper started out making free VST plug‑ins under the name Vellocet in the late '90s, and later moved on to developing effect modules for FXpansion's highly acclaimed Guru and BFD2 drum instruments, before working on the same company's D‑CAM: Synth Squad, which received a rave review in the January issue of Sound On Sound.
The Glue is based on the highly acclaimed SSL bus compressor. Schematics from the SSL E‑series bus compressor have been used to build the digital model, but instead of modeling the non‑linearity of the VCAs, a 'perfect' VCA has been modelled, which makes The Glue sound more like the modern SSL XLogic G‑series compressor. During the process of creation, an XLogic hardware unit was used to compare and tweak the performance of the plug‑in. The two pretty much share the same settings except that there are additional attack and release settings in the plug‑in, along with a high‑pass side‑chain filter, Dry/Wet control, and compression Range control.
The classic three‑step ratio knob is positioned in the middle of the interface, and at its 2:1 setting a relatively subtle soft‑knee compression is applied. At 4:1, the compression becomes more obvious, and at 10:1, The Glue is basically a peak limiter. The attack settings range from 0.01 to 30 milliseconds (the fastest setting is not present in the original hardware). As for the release settings, they range from 0.1 to 1.2 seconds, with the classic auto‑release at the clockwise extreme. Threshold and make‑up gain are represented by two knobs but, more interestingly, there is a compression range knob, which limits the maximum amount of compression applied, regardless of the other settings.
The side‑chain EQ is a gentle 6dB/octave filter with a cutoff frequency that can be set from zero to 2000Hz, and it can be applied to the internal signal or an external side‑chain signal. When you press the external side‑chain button, the plug‑in reports one or two extra inputs — depending on whether it is set up for mono or stereo processing — making it possible to use any signal to control the compressor. Unfortunately, the VST3 standard is not yet supported, so the success of setting up an external side‑chain very much depends on the DAW host and its ability to route audio in a flexible way. To catch overshooting transient peaks, there is a peak clipper available with zero attack and release time, and with a fixed infinite ratio and medium knee. It's basically a fixed waveshaper that is linear up to ‑2dB, has a smooth curve to ‑0.5dB, and is then horizontal. The topmost compression meter displays the depth of compression in an RMS-level fashion, and clicking the display will show the amount of peak compression too.
During the test period, I used The Glue on a bunch of different instruments and group channels, with great success. One of my mixing projects had four different bass guitar tracks mixed into one mono group channel, and The Glue helped me to even out the levels of the different bass tones without introducing any compression artifacts. On the same project I was able to tighten up the lead dubs and choirs without losing any punch, which was a nice surprise. Normally I would resort to softer limiting to even things out, but that requires great care and tweaking in order to avoid losing some impact. The Glue made it easy because of its ability to handle both transients and prolonged energy bursts with transparency and clarity. Just a tad of drum bus compression made the drums sit together without losing the thud of the kick or the smack of the snare, and I was able to mix the cymbals and hi‑hat louder in the mix without them taking over the show. Sometimes I just needed a gentle touch of compression, and the Range control made it possible by limiting the compression to a few decibels.
Using the Mix control, it's possible to blend the uncompressed and compressed signals, thus producing parallel compression — a very effective way of adding energy without squashing the transients. I find it useful on drums and acoustic guitars when they need some extra energy, but it's actually useful on most instruments: it's just a matter of finding the right compression and balance between the compressed and uncompressed sounds.
During the test period, my only complaint was that browsing and loading of presets could be made better, because when the preset screen was open, the whole DAW interface locked up.
During the test I did not have access to the hardware unit on which The Glue had been modelled, namely the SSL XLogic compressor, but Andrew was gracious enough to send me some of his own measurements and recordings of the hardware and his plug‑in. In comparison, I first found them fairly similar in sound, but The Glue lacked some authenticity, and the transients weren't as smooth‑sounding. Andrew pointed out that the processing wasn't using any oversampling, and consequently a low‑level aliasing was present, which added a mild harshness to the transients and smeared the finest details of the source. So I asked if he could make an oversampled version of the plug‑in, and a couple of days later it arrived in the mail. On trying it, I found that it sounded very much like the hardware sound clips, at the cost of increased CPU usage and about 2ms latency.
To further analyse the benefits of using oversampling when applying dynamic processing, I made a fast shootout between the two versions of The Glue. In comparison, the oversampled processing retained a better stereo width, more transients and a slightly greater depth in the mid‑range. I should point out that the differences were small, and on some sources I preferred the non‑oversampled processing, due to the coloration of the transients. Oversampling will be available as an option in a coming update of The Glue, and by the time you read this it will probably have been implemented.
There are a lot of products on the market — both digital and analogue — trying to mimic the performance of the classic SSL bus compressor, so I decided to line up a few of them in a proper shootout. The digital contenders were the two versions of The Glue, the UAD 4k Buss Compressor and the Waves SSL Compressor — the two latter being used by many industry professionals. Just for the fun of it, I also included two of my own analogue compressors: the ultra‑transparent TK Audio BC1 and a home‑made GSSL compressor based on the SSL schematics, but with old Dbx 202C VCAs. Both of these units offer basically the same settings as the original SSL hardware.
The first test was an already heavily processed drum loop with lots of low end. I used my army of SSL clones to smash it even further at a ratio of 10:1, with 3ms attack and 0.1s release times, and a threshold set so that the meter indicated about 15dB of compression. Even though the differences were small, the oversampled Glue felt a bit more alive compared to the non‑oversampled. The UAD plug‑in had a nice release curve that made the compression pump with the drums and it added some mid‑range, but at the same time the hi‑hats were suppressed a little bit. The Waves plug‑in sounded flat and grainy compared to the other plug‑ins, and lacked some definition. The BC1 showed the best stereo width and definition and was somewhat smoother‑sounding than The Glue, while the GSSL had a raw, pumping sound of its own, making it great for effect compression.
Next up was a stereo‑dubbed acoustic guitar. This time I wanted to use the auto‑release to tighten up the sound without squashing it too much. The settings were a ratio of 4:1, 1ms attack, auto‑release and a maximum compression of about 6dB. The stereo width and definition was a tad better with the oversampled plug‑in, but in this case, the coloration of the transients in the non‑oversampled plug‑in somehow suited the acoustic guitar. The UA plug‑in also added some coloration, making the sound more beefy and sustained, which I also liked. The Waves plug‑in, however, sounded flat in comparison, and lacked some stereo definition. The BC1 made the guitar a bit smoother without losing any definition or stereo width, sounding maybe a bit more compressed compared to the others. The GSSL made the transients a bit more gritty, but in a good way — at the expense of slightly less well defined stereo width and low end.
The third test was a full mix that was compressed in each case using a ratio of 2:1, 10ms attack, auto‑release and about 2dB of compression. Both versions of The Glue packaged the mix in a very nice way, and the only differences were a slightly more defined and firmer low end, wider stereo width and marginally more open sound in the chorus with the oversampled plug‑in. The UAD 4k Buss Compressor added some low end that pushed the mix forward in a nice way. The Waves compressor sounded great in the verse but lost a little bit of low‑end definition in the chorus, where it also added a tiny bit of graininess. Because of its three‑dimensional depth and stereo width, the TK Audio BC1 came out sounding 'like a record', which was no surprise to me. The vivid definition of the choirs set it apart from the other sound clips. Last but not least, the GSSL compressor sounded too coloured, and lost both low end and stereo definition.
When I downloaded The Glue, I wasn't expecting anything out of the ordinary, but the more I used it, the more I realised how versatile it was. It not only performed impeccably on bus‑compression duties, but was also able to tighten up bass guitar, acoustic guitar, drums and vocals without adding a 'sound'. In my opinion, transparent compression will never go out of fashion because what it basically does is to bring up more of the music — without adding compression artifacts. Compared to similar plug‑ins, The Glue sounds more open and has a more defined stereo width — and it certainly provides 'the glue' on a variety of instruments. What I really like about The Glue is the auto‑release setting, because it makes it easy to apply compression that just tightens up the sound in a very useful way. There is a demo version of the plug‑in available at Cytomic's homepage, in VST, AU and RTAS formats. It's well worth a try!
There are a bunch of plug‑ins that share the same architecture and layout, including the UAD 4k Buss Compressor, the Waves SSL Comp and the SSL Duende Stereo Buss Compressor. All three cost more than The Glue, and two of them require DSP hardware.
I recorded the results of my shoot-out to give SOS readers the opportunity to compare The Glue with the UAD 4k Buss Compressor and the Waves SSL Compressor. Two analogue equivalents are also included in the test: the ultra‑transparent TK Audio BC1 and a home‑made and very colourful GSSL compressor with old Dbx VCAs. The sound clips can be found on the SOS web site at /sos/nov10/articles/theglueaudio.htm.