The big squeeze
David Bowie's legendary producer Tony Visconti once called compression "the sound of rock", and he wasn't far wrong. Compression is used all over modern music (some say too much), and is a sort of secret weapon for achieving a professional sound.
Compressor plugins vary in complexity, from simple more-or-less VSTs such as Sausage Fattener, to those that provide a user-definable volume threshold above which the effect will kick in, and a ratio that describes the difference between the unprocessed (or 'dry') signal and the effected (or 'wet') output.
Compression should be used whenever something requires taming: vocals are a given, unless your singer has great mic skills, while drums and often entire mixes can also be moulded into shape with a compressor.
So how do you decide which plugin is right for your mix? Over the course of this feature, we'll take a look at some of the best - both old and new - to help you through the jungle.
Slate Digital Virtual Buss Compressors (PC/Mac, $250)
Let's kick off with a stunning triple-decker unit, and one of the best software emulations of analogue gear that we've encountered to date.
The VBCs are unofficially sourced from three classic designs: the SSL 4000 Console Compressor, Focusrite's original Red 3 Stereo Compressor/Limiter, and the valve-based variable mu of the Fairchild 670 and Manley 'Vari-Mu' units.
During development, Slate made a conscious decision to focus on non-linearities like harmonic distortion, phase distortion, frequency alteration and noise, as well as the underlying compression characteristics - so in theory, we really are talking 'warts and all'.
All three units offer interesting effects on the input signal even when they appear to be delivering zero gain reduction. It's when you start compressing, though, that the personality comes through. FG-Mu is just beautiful across drum overheads, drum sub mixes and overall mixes. The high-frequency sheen is accompanied by a low frequency "glue", and there's plenty of flavour even at gentle settings.
VBC presents everything you need to compress your master buss, sub mixes and plenty more besides with real character and analogue authenticity.
112dB Big Blue Compressor (PC/Mac, $149)
The Big Blue successfully combines the warmth and colour of a valve unit with the bite and pump of a modern compressor, resulting in a big, weighty, powerful sound that's best summed up as huge and in-your-face.
BBC offers a great features set, including a high-pass filter for shaving bass energy off the sidechain signal, a variable Knee control that gives greater response precision and bite, and a Choke control that models the way valve compressors work to stifle transients.
Using these options together unlocks the broad potential of the BBC: working with drums, for example, the combination of Drive, Threshold and Choke will enable you to be extremely refined in the level of compression you apply. Meanwhile, Big Blue's RMS detection mode can give a natural level control to bass, pianos and other stereo signals.
BBC also offers several stereo-centric features, as well as Mid and Side switches that activate separate compression for the mid signals (such as vocals) and side signals (such as the air and space of a track) respectively.
Especially snarling on up-front rock and dance tracks, Big Blue Compressor sounds amazing, can be pushed impressively hard and boasts a great feature-set.
Cytomic The Glue (PC/Mac, $99)
The Glue is essentially a superb emulation of SSL's famous hardware bus compressor, with a pretty big exception: because it's not endorsed, Cytomic has been free to include some additional features that you won't find on the real thing.
Of the 'new' features, the sidechain filter affects both internal and external sidechain signals and enables you to roll off low frequencies right up to 2kHz. This works well at reducing pumping on mixes, and at fine-tuning low-end heavy sounds.
Meanwhile, the Mix and Range controls offer some versatile compression flavours - meaning that the plugin is handy for individual instruments as well as the master bus - and the PeakClip option with its associated red LED is useful if used carefully.
Combined with a simple interface, The Glue's great sounding SSL emulation, responsive mastering and flexible extras make it an affordable and justifiably popular choice.
READ: Cytomic The Glue review
Softube Tube-Tech CL 1B (PC/Mac, $329)
The CL 1B is a plugin emulation of a hardware equivalent by the same name, designed in conjunction with its makers Tube-Tech, and said to meet their exact standards. It's a fantastic, CPU-friendly plugin that's capable of both subtle containment and excellent audible colour.
Among the CL 1B's notable details are a simple external sidechain selector that can be run in mono or stereo, realistic controls and three attack/release presets - of which 'fixed' mode is especially handy for dialling in useable compression.
The CL 1B is adept at both subtle and audible compression, with attack and release characteristics. We tried the plugin on on a number of sounds, including acoustic guitar, drums, piano, vocals and bass, and they all benefited in one way or another.
Overall, the CL 1B really is a fantastic compressor plug-in that's capable of both subtle containment and excellent audible colour. It doesn't come cheap, but when you consider that it weighs in at a fraction of the cost of a hardware CL 1B, the price becomes easier to swallow.
FabFilter Pro-C (PC/Mac, £124)
Although there are plenty of fine-sounding compressors around, they rarely give you much in the way of helpful visual feedback. Enter the animated graphical display of of the FabFilter Pro-C, which shows you just what effect it's having on your signals, making it a breeze to set up.
Pro-C is a truly modern and innovative VST/AU/RTAS compressor that's program-dependent. This means that the effect of the compression adapts to suit the audio input, for maximum dynamic manipulation with minimal unwanted side effects.
There are three individual compression styles onboard: Clean goes for clinical accuracy with a transparent sound, Classic offers authentic analogue warmth, and Opto shares its attributes with a vintage optical compressor, having a very soft knee and a somewhat slower response.
Meanwhile, the display makes using compression easier than ever. You can watch the peaks and troughs of the audio signal rush by while tweaking the MIDI-learnable controls, quickly reaching the desired compression effect, almost as if by magic.
Whether you're a compression freshman or a professor of pump, Pro-C gets top marks.
READ: FabFilter Pro-C review
Kush Audio UBK-1 (PC/Mac, £90)
The UBK-1 brings the sort of colour you'd naturally get in the analogue domain to a mix. Generally, it's very warm and very fat, and it particularly excels when deployed for heavy drum mishandling or, alternatively, used lightly on spacious productions.
It's a three-stage processor: firstly, the Saturation processor generates pleasant harmonic distortion, softens transients without losing too much attack, and includes a wet/dry mix control for parallel processing.
A choice of five compressor models is on offer; each has its own particular response character and a descriptive name (Splat, Smooth, etc). Pick one, set the dial somewhere between Mild and Intense, and adjust the wet/dry mix - compression doesn't ever get much easier than this.
Finally, the Density processor adds subtle substance to the top or mid-range of the sound. Essentially a combination of frequency-selective compression and saturation, it's heavily dependent on the results of the previous sections.
Sonically stunning, UBK-1 excels at bringing authentic, flavoursome analogue character to drums, acoustic instruments and mixes.
READ: Kush Audio UBK-1 review
Sonoris Mastering Compressor (PC/Mac, €199)
Mastering Compressor offers the cleanest compression we've heard to date, and it's capable of extreme punch when required.
In testing, the first thing that struck us about Mastering Compressor was its flexibility. Operated via a clean, clear and decidedly old-school interface, it allows ratios from 1.01:1 to 100.0:1, and then Inf:1 (for use as a brickwall limiter).
The threshold goes down to -60dB in 0.1dB increments, and the attack and release knobs can be set to lightning fast or invisibly slow.
Mastering Compressor has two knee controls: Knee1 softens the default hard-knee operation so that the compression amount is applied along a gentle curve as the signal approaches the threshold. Meanwhile, Knee2 gradually returns the loudest parts of the input signal from their compressed ratio to a 1:1 ratio (in other words, no compression) as they exceed the threshold. This is useful for letting peak transients through, giving further transparency.
Transparent and intelligent, Sonoris' Mastering Compressor is one of the very finest dynamics tools we've ever loaded on our master bus.
Klanghelm DC8C 2 (PC/Mac, €20)
To budget-conscious engineers in the know, Klanghelm's bargain-priced DC8C compressor has been a must-have since its initial release in 2012.
In Easy mode, DC8C 2 looks much like any other compressor, with the usual array of dynamics-shaping parameters on board: Threshold, Ratio, Attack, Release, Mix, etc. Just below the VU meter section, though, is a row of buttons that switch between four 'compression styles'.
These determine the character of the processing, ranging from utterly transparent (Smooth) to punchy and percussive (Punch), "transient-spitting" (Snap) and heavily distorted (Crush). The versatility that these four modes bring into play is impressive, and Easy mode in general is indeed very simple to negotiate.
Switch to Expert mode and a raft of extra controls are added to the interface, turning DC8C 2 into one of the most tweakable compressors we've seen. The sidechain, for example, gets added to with frequency Tilt, and the RMS Time knob lets you set the 'rigidity' of input signal analysis anywhere between RMS and peak detection.
Being so absurdly flexible, it would be disappointing if DC8C 2 didn't sound great, but happily, we can report that it really does. Whether it's called on for transparent levelling, punchy character enhancement or brutal signal squishing, it constantly holds its own against plugins costing far more.
Meanwhile, if you're after a great free plugin with bite, we can heartily recommend the DC8C's little brother - a cut down version that's comparable to its Punch mode - called the DC1A.
REVIEW: Klanghelm DC8C 2 review
Cakewalk CA-2A T-Type Leveling Amplifier (PC/Mac, £79)
Renowned for its transparency and musicality, the Teletronix LA-2A is a - possibly the - classic opto compressor with tube amplification. The CA-2A is Cakewalk's latest plugin emulation of it, a port of their previous Sonar-only version (the PC2A) into VST/AU plugin formats, joining their fabulous Z3TA+ synth on the cross-platform train.
The CA-2A features the standard set of LA-2A controls: Peak Reduction (threshold), Gain (gain make-up), and two Ratio settings (Compress and Limit). In addition, you also get access to the LA-2A's 'emphasis' circuit via the R37 control; an external sidechain; and a Photocell Memory setting with Classic and Fast Reset options.
The first thing to note about the CA-2A is how responsive the meter is, and similarly the controls. Ergonomically, this is arguably the best LA-2A emulation yet. Sonically, we found it to be pretty neutral with no gain reduction applied. Once you start to wind up the Peak Reduction, though, the CA-2A really comes into its own, with the fastest transients handled very sympathetically.
Ultimately, there are so many great LA-2A emulations out there now that personal developer preference could well be the deciding factor in your choice of which one to buy. Don't let that rule the CA-2A out of your investigations, though: it's one of the best out there.
FXpansion DCAM Dynamics (PC/Mac, $99)
DCAM Dynamics is a quartet of component-modelled compression plug-ins: BusComp, an SSL-style bus compressor; ChanComp, an 1176-style limiting amplifier; CrossComp, a frequency-conscious buss compressor; and EnvShaper, a transient shaping compressor.
BusComp is intended for use on group and master busses. It's as easy to use as its inspiration, with all the expected controls in place, including the indented Attack, Release and Ratio knobs, the latter of which gives only 2:1, 4:1 and 10:1 options. It sounds every bit as good as The Glue on drum busses and full mixes.
ChanComp is also largely defined by its parametric limitations, just like the hardware it apes. With Ratios of 4:1, 8:1, 12:1, 20:1 and 'Nuke' (emulating the 1176's high-impact 'all button mode'), and no threshold control, you can't really go wrong.
CrossComp aims to provide frequency-conscious compression without the hassle of a full-spec multiband plug-in. Clearly the creative member of the team, its combination of parallel processing and frequency-conscious compression can work wonders on full drum tracks and sampled loops.
Finally, EnvShaper takes its inspiration from SPL's Transient Designer, empowering us with the quasi-magical ability to raise/lower the transient and sustain stages of the input signal. The controls couldn't be simpler, and though its most obvious application is the lengthening or shortening of drums, basses, short synth sounds, pianos and even guitars are fair game.
DCAM Dynamics proves that top tier track/mix processing really doesn't have to carry a hefty price tag. The modelling is spot-on, the sound is gorgeous, the usability is excellent and the range of compression bases covered is broad yet individually focused.
Slate Digital FG-X (PC/Mac, $199)
Maximising loudness is very much a part of contemporary mastering, and it's typically done using limiters, clipping, saturation or a combination thereof.
Dissatisfied with these approaches, Slate Digital put their heads together to devise an alternative: FG-X. This is a single plug-in that houses FG Comp, a master bus compressor, and FG Level, which offers a new type of maximisation called Intelligent Transient Preservation (ITP), a sort of smart saturation process. Rounding it off are peak, RMS and VU meters.
Sonically, FG Comp is audio butter - it's one of the smoothest, most transparent compressors we've heard. It's hard to make it pump, yet somehow it still grabs the transients in all the right places.
Unlike a lot of compressors, the gain reduction meter is set to show a very small range of just 3dB by default, which is spot-on for most mastering situations. That's a sensible touch.
We found FG Comp equally adept at providing subtle mix 'glue', gentle level riding, and giving material a 'compressed' feel without being obnoxious.
Interestingly, it's one of the few master bus compressors we've found to be useful with complex, full-on material like extreme metal, as it can control these mixes without simply overreacting. Oh, and it's worth a try on instruments, too - we like what it can do on a drums bus, for instance.
Combined with FG Level, FG-X preserves punch and dynamic definition like nothing else. Anyone who does mastering needs to check it out.
DMG Audio Compassion (PC/Mac, £149.99)
Compassion is the most configurable dynamics plugin we've encountered, offering compression, expansion/gating, transient shaping, and limiting/clipping. It's got over 80 parameters that can be used to approximate the sound of any compressor, reckon DMG.
Thankfully, you can treat it as a normal compressor to begin with, with the advanced controls hidden. Flick through the presets, however, and you'll see the graphs change, indicating the flexibility of the advanced mode - in which the shape of attack and release curves can be modified extensively, with the results shown on the plugin's Response Graph.
It's all a bit overwhelming at first - we strongly recommend reading the manual. However, the range of compression styles you can dial in is vast, ranging from super-precise, clean digital on through to outrageous, pumping analogue tones.
This is a flexible, excellent sounding compression plugin, and a useful transient shaper too.
Native Instruments Vintage Compressors (PC/Mac, €199 )
As befits its name, Native Instruments has traditionally been known for cutting-edge plugin instruments, rather than effects. Yet behold: in 2011 it took a bold leap into vintage outboard hardware modelling territory, with this trio of plugins - all featuring DSP guts from modelling experts Softube.
The VC 76 is an emulation of a UREI 1176 - and indeed, the full palette of that compressor's sounds can be achieved, from precise vocal taming to pumping drum overheads. Like the real thing, adding bite to bass is a breeze, and the fast attack settings have been captured very well.
The VC 2A models the famous Teletronix LA-2A, and on vocals, it instantly delivers the seductive and often quite audible squeeze that its inspiration is famous for, while the sidechain low cut is definitely a useful addition when compressing bass dominant sounds.
Finally, the VC 160 is a self-styled 'bold and dirty' compressor that's based on the VCA dbx 160, and is best used for adding extra punch to kicks and snares.
FIND OUT MORE: Native Instruments Vintage Compressors
Vengeance-Sound Multiband Compressor (PC/Mac, £85)
Multiband Compressor (MBC) offers up to four bands of precise dynamic control. On the surface, it's a pretty standard affair, with compression or limiting for each band and a master limiter on the output. Take a closer look and you'll uncover a huge range of options.
You can set the slope of the filters that divide the bands, from a very loose 6dB (resulting in lots of crossover from one to another) to a ruthlessly surgical 96dB. This setting will depend on the style of music you're mastering and the adjustments you're making.
Then there are the dazzling meters and displays. It's fair to say that this plug-in looks awesome in action. The meters give genuinely useful visual feedback on the levels of signals going into and out of sections as well as the amount of attenuation going on.
It's as comprehensive a visualisation system as we've ever seen and it makes MBC fun and exciting to use. Meanwhile, there's a huge range of presets, ranging from fun and creative to the (slightly useless) overall mastering templates; usefully, there are individual band presets too, for both compressor/limiter and DPC.
It's not as warm as some, but taking everything into consideration, MBC is an incredibly versatile and desirable plug-in, and for this type of processor, the price is quite reasonable too.
Solid State Logic X-Comp (Mac/PC, £129)
X-Comp, like its frequency-shaping brother, X-EQ, features a clean interface with plenty of bells and whistles.
X-Comp is immediately notable for its metering. Input and output meters are located on either side of the GUI, and each displays peak, RMS and dynamic history (showing the largest and smallest recent signal peak). Also included is a gain reduction display, but far more useful is the inclusion of an amplitude histogram named I/O Diff that shows the dynamics of the input and output signal set back-to-back.
This enables you to see exactly what effect X-Comp is having - you can literally visualise, for example, a signal going into X-Comp with dynamics across the entire range and coming out of the other end with its energy mostly concentrated in the centre of the spectrum.
In the mix, X-Comp runs the gamut from the freaky effects of the SSL Listen Mic Compressor right up to 'brick wall with class' limiting, close to - if not exactly the same as - the legendary SSL Bus Compressor.
It also throws in many subtle choices and masses of options, delivered with sweet-sounding analogue-style tone, and is enjoyable to use, once you've got the hang of it.