The compressors most of us use are software plugins that come with our DAWs, and they do a great job. The flexibility to be able to put as many compressors as we like, anywhere in the audio chain, at any time, is the sort of luxury the engineers who mixed most of our favourite classic tunes could only dream of.
But these simple software compressor plugins bear no relation whatsoever to the hardware compressors that those same engineers still use in their mixing right up to the present day. These days, it’s pretty easy to mathematically define a compressor in terms of ratio, attack and release times, and so on, and build a plugin that slavishly follows that definition.
Back in the golden age of audio, though, that wasn’t the way things were done. Compressors were built with electronic components – transistors, resistors, amplifiers and valves – and these components simply couldn’t offer the infinite control and flexibility that a computer can, so designing compressors was a fine art, a constant process of balancing the technical requirements of the hardware against noise, headroom and cost.
If you listen to a simple digital compressor with a ratio of 1:1, the chances are its output will sound exactly the same as what you put in, even at a high level. A compressor such as the classic Fairchild 670, however, uses no fewer than 20 valves. This means that even when it isn’t compressing things, its output may well cause all kinds of lovely colouration and sonic changes that have nothing to do with compression.
It’s ‘extras’ such as these that explain why big-name engineers love the sound of their expensive racks of analogue hardware. However, an increasing number of software emulations from the likes of UA, Waves, Softube and many more will offer great emulations of this hardware and are a great route into the world of ‘proper’ compression, without the extortionate price tags of that classic gear.
5 of the best hardware compressors
A superb hardware compressor with a very fast attack. Sounds great on drums, or vocals and bass with a slower attack and release.
A classic model now re-issued by Universal Audio, featuring a choice of transformer or optical compression, plus valve amplification for warmth. Great on vocals and bass.
Fairchild 670 Valve Limiter
Contains more than 20 valves! Pioneered by Geoff Emerick on the Beatles’ recordings. Great on vocals, drums, or anything else, if you can afford it, that is…
The dbx 160 is a classic vocal compressor. It’s fast and clean, but take care it doesn’t distort the signal.
SSL G-Series Master Compressor
This archetypal two-buss compressor is great for gluing things together. Mix through it but don’t whack it on afterwards, and be prepared to spend time learning it.
5 of the best software compressors
Emulations of the Urei 1176 (Comp FET76), DBX 165A (VCA65) and Gates Sta-Level (Tube-STA). A classy, authentic trio of bona-fide audio engineering classics.
Something of an industry classic in the world of plugins. It’s more expensive, but watch out for promo offers on the Waves website.
UA 175-B and 176 Tube Compressor Collection
Another set of emulations of classic gear, this time the all-valve forerunners to Bill Putnam’s more famous 1176 design.
PSP Audioware and oldTimer MB
A multiband version of PSP’s versatile oldTimer ME, with three frequency-limited instances of the compressor allowing intricate processing tasks.
What you already have
Most modern DAWs such as Logic, Pro Tools, Cubase etc will do a great job of controlling dynamics. Make sure you’ve mastered these before splashing the cash on expensive alternatives, but don’t expect hardware character from them.