When it comes to processing, there’s still nothing like a piece of actual hardware to impart that true “analog sound” to a recording or mix, and hardware Compressors are among the most distinctive pieces of analog gear out there. This article will survey seven of the best high-end hardware compressors around—most are classics, and some are out of production, but vintage units and modern reissues and clones still provide availability for current users who just have to have their favorite toy.
The LA-2A usually places either first or second on most engineers’ desert island compressor lists. It’s the classic smooth compressor, combining simplicity with can’t-miss sound and analog warmth.
The LA-2A is an optical compressor—as you know, compressors all employ detection and control circuits to determine when signals cross Threshold and apply the appropriate gain reduction. The LA-2A uses a T4 optical attenuator—this is made up of an electro-luminescent panel (an internal light, basically), coupled with a photoresistor. The light glows in response to incoming signal level, and the resistor reduces gain accordingly. The particular response of the light and resistor determines the specific response characteristic of the compressor. In fact, it’s all automatic—there are almost no front-panel controls, just a knob for increasing compression and the usual make-up gain—no Ratio, no Attack & Release, it’s all determined by the circuit.
The T4’s response gives the LA-2A a relatively slow attack (around 10 ms or so), and a slow, gradual release, which makes for transparent gain control—it can squeeze a signal pretty hard without the audio really sounding “compressed”. That quality has made it especially popular for vocals, though it’s also favored for bass, and many other instruments as well. One of the secret ingredients of the LA-2A—that it shares with many of the classic/vintage compressors in this list—is that its response is “program-dependent”. That means that the response varies with the incoming signal, kind of continually optimizing the compressor response as the audio varies. Add in the LA-2A’s tube output section, which lends it that sought-after analog warmth, and you’ve got a true classic on your hands.
LA-2As are still in production, from Universal Audio’s hardware division—UA is the current incarnation of the company that made the original, and their reissues are spot-on. They—and a host of other companies—also make virtual emulations of the unit (actually, all the compressors in this list are also modeled in software), but here I’ll just focus on the real (physical) thing. Take a look at the racks in almost any medium-to-large studio, and you’ll see the LA-2A well-represented. Short of grossly overdriving it, you really can’t get a bad sound out of it, and the hardware unit is perfect as a front-end compressor for vocals, controlling levels transparently, without imparting an overly compressed quality that might turn out to be too much later on in the mix.
The other “king of compressors” is the Urei 1176. This is the other side of the compression coin from the LA-2A. Where that unit is slow, smooth, and gentle, the 1176 is fast, edgy and aggressive.
Utilizing transistorized FETs (Field Effect Transistors) for its circuitry, the 1176 defines punchy compression, and is a favorite on drums, where it’s known for creating “big” aggressive drum sounds. With fast & faster Attack (in the microsecond range) and Release times, this unit can be pushed, for a real in-your-face quality. It’s got a more typical layout, with Input and Output Gain, Attack & Release controls, and four Ratios—4:1, 8:1, 12:1, and 20:1. A popular trick is to push all four Ratio buttons in at once—the famous “All-Buttons Mode”, which lets you push it even harder on drums, while still preserving snap and impact.
Though it’s primarily known as a drum compressor, the 1176 can also work its magic on many sources, like voice, bass, and acoustic guitar, among others. Besides UA’s current model (another spot-on reissue), many other companies produce both clones and similar FET-based designs, that capture some of the aggressive vibe that’s made the original hardware so ubiquitous in studios large and small.
As a hardware piece this is a rare bird—working vintage units, if you can find one, have been known to go for tens of thousands. The Fairchild 660/670 (mono/stereo versions) combine the more full-featured layout and flexible Attack & Release times of the 1176 with the tube warmth of the LA-2A for a really special quality. The original 670 hardware fills its 6 rack spaces with 20 tubes and 14 transformers, and all that glass and iron gives it a truly analog character.
The Fairchild (like the LA-2A and 1176) is another program-dependent design, and combines the best qualities of both of those units—the LA-2A’s warmth with the 1176’s punch. It shines on just about anything you run through it. Back in the day, the stereo version (670) was popular for mastering—it even features an option for M/S (mid-side) operation, which was used for controlling the vertical/lateral aspects of the groove when mastering for vinyl.
Fairchild compressors utilize what’s called a variable-mu design. That means that gain reduction is accomplished by varying the bias of a special type of tube, a variable-mu model (“mu” means gain), in response to incoming signal levels. This is actually a very old design, and it’s responsible for much of the Fairchild’s specific character. Vintage units are nowhere near as common as the other two compressors I’ve mentioned so far, and there are few hardware clones—the quality imparted by all those tubes and transformers would be prohibitively expensive nowadays—but a good modern alternative is available from Manley—their aptly named Vari-Mu model.
dbx’s David Blackmer is generally acknowledged as the “father” of modern VCA-based compressor designs (yes, that’s the same type of circuit found in analog synths, here applied to gain control in compression). His improvements to earlier, noisier, VCA circuits led to the development of the dbx 160 compressor, which set the bar for fast, tight VCA compression, which became the standard for professional units (until the vintage craze brought back all those older, flavorful designs).
The original 160 was a simple design—it lacked Attack & Release controls, but brought a fast, tight compression characteristic to the table, perfect for clamping down on drum and bass transients, and really controlling peak levels. A more transparent transistorized design, the 160 doesn’t have the kind of flavor of some of the tube/FET units mentioned, but it does have its own character, thanks to certain nonlinearities in the circuitry.
The 160 has what’s known as a “hard-knee” response—when the signal crosses Threshold, the compressor immediately clamps down. Most of the other units I’ve covered have a “soft-knee” response—compression kicks in more gradually, starting slightly below Threshold (at a lower-than-set Ratio), and increasing until it reaches the set value, a bit above Threshold. This can reduce “pumping”, a slightly stuttering compression artifact that can occur when the signal vacillates around Threshold level. A later model dbx design, the 165, took the basic 160 circuitry and added their version of this, which they termed “Over-Easy” response, and it’s this sound that many people associate with dbx compressors, more than the hard, pumping character of the 160. Of course, in the right hands, a little pumping can make for a great effect, and it’s probably why the 160 still remains so popular, long after it went out of production.
The original version of this popular compressor was found strapped across the main stereo output of SSL’s classic 80s-era analog consoles, the 40000G series. It was a dual-VCA design, intended to subtly squash the full mix, and it became immensely popular, even earning itself a nickname—“The Glue”.
This referred to its purported capability to magically “glue” all the elements of a mix together, adding cohesion and a little gentle push, and many mixers found it irresistible—so much so, that some even like to build up the mix through it, rather than applying it at the end of the process (the more common, and arguably, better approach).
Though intended primarily for use on full mixes, the SSL Buss Compressor can also sound great on drums, when patched into individual tracks. Currently, a version of this hardware circuit is available as a rackmount unit from SSL, and many clones are out there as well, trying to capture the magic of the original.
The 2254 was also found in vintage consoles, this time, naturally, in (80-series) Neve consoles of the '70s. They might not be as familiar to most modern engineers/producers, but these hardware units (the stereo 33609 is an evolution of the 2254) had their own distinctive sound and response, and are worth trying out, if you ever have the opportunity (even hardware clones or software emulations).
The original Class A design employed a diode bridge and multiple transformers, and provides a tasty edge when driven—the inherent nonlinearity and relatively high distortion of the diode-bridge attenuators, coupled with the warmth from the Transformers’ iron, gives these designs their own particular analog character, a “creamy”, “buttery” sound that can nicely enhance many different instruments and sources, including use on the mix bus. Currently, reissues are available from latter-day Neve.
While each of the vintage designs in this list has its own particular, distinctive analog character and response, Empirical Labs’ Distressor is the opposite—it’s a versatile compressor that offers a wide range of different responses and characters, even emulating the essential qualities of many of the vintage units I’ve mentioned.
Originally introduced in 1996, the Distressor sought to ameliorate the cold, clean character of modern analog and digital technologies by, in effect, modeling (via analog circuitry) the warm characteristics of older, classic compression gear. Among its eight modes and compression curves are takes on vintage optical response, classic tube warmth and even tape saturation, and its “British Mode” even apes the distinctive response of the 1176 in “All-Buttons Mode”.
This versatility has made the Distressor a modern classic, for those in the know, and if you had to choose just one compressor to handle all dynamics requirements, this one might just do the trick.
Of course, there are many other deserving compressors that I could have included, if I wasn’t going to stop at 7—the API 2500, TG1 12345 Limiter (Chandler TG-1), and even the excellent budget-minded RNC. But despite the age of many of the designs, these 7 compressors have all earned their inclusion in any best-of list, and any of them would serve well in today’s modern studios and production rooms.