Exploring Logic Pro X's Compressor Circuit Types

Logic Pro's built-in compressor has a lot of sound shaping potential below the surface. Joe Albano reveals the ins and outs of its circuit types.  
The Logic Compressor.

The Logic Compressor.

The Logic Compressor, at first glance, is a fairly standard processor. All the usual controls are there, and there’s even an extra stage, a separate Limiter, at the output. But there’s an almost hidden extra that gives this plug-in a great deal of added flexibility and nuance of sound quality.

The Logic Compressor’s Circuit Types.

The Logic Compressor’s circuit types.

A few years back,  Apple, with little fanfare, slipped in a Circuit Type pop-up menu. This added to the traditional bread-and-butter Compressor behavior (Platinum), by offering the ability to mimic the characteristic response of various classic hardware compressors. Had they re-skinned the GUI with photorealistic images suggestive of these well-known models, this new feature would have undoubtedly made a bigger splash when it was introduced.

In the world of vintage hardware compressors, there are three main circuit types, and the Logic Compressor does them all. In addition to its original, generic compressor design—Platinum—it simulates Optical Compression (Vintage Opto), FET-based compression (Vintage FET), and VCA-based compression (Vintage VCA). Besides these classic models, there are additional, more specific models labelled Studio FET and Studio VCA. None of these claim to be a circuit-by-circuit clone of original analog hardware, as some plug-ins do, but they do promise the essential response and character of those designs. The Studio models are rumored to be based on particular hardware units, though no definitive word has ever come down from Logic’s designers.

Opto Compression

In the hardware world, the dean of opto compressors is the Teletronix LA-2A, known for its warm sound, thanks to the all-tube design, and its smooth, transparent compression, thanks to a circuit that uses an internal optical (light-based) assembly that controls detection and gain-reduction. 

The Teletronix LA-2A Opto Compressor.

The Teletronix LA-2A Opto Compressor.


The Logic Compressor Vintage Opto Mode.

The Logic Compressor Vintage Opto mode.

Opto designs are many engineers’ go-to models for vocal compression, and the Vintage Opto model offers up that kind of response—transparency is the word here. Besides vocals, opto compression is great for bass, and any track that you want to compress without having the processing be especially noticeable. A soft-knee setting would undoubtedly provide a response closer to the original circuitry, where the response characteristic actually varied with incoming signal levels—one of the “secret ingredients” of many vintage compressor designs.

FET Compression

On the other side of the coin are FET compressors. While an optical design’s attack and release tend to be slow and subtle, FET (Field Effect Transistor) circuitry is fast, for a much more potentially aggressive compression character. 

The UREI 1176 FET compressor.

The UREI 1176 FET compressor.

The real-world FET model of note is the UREI 1176, which, like the Logic version, can add some real “push” to a track. FET designs, while they sound great on many instruments and vocals, are known especially for the big, fat sound they can impart to drums.

The Logic Compressor’s Vintage FET Mode.

The Logic Compressor’s Vintage FET mode.

The Logic Compressor’s Studio FET Mode.

The Logic Compressor’s Studio FET mode.

Logic’s Compressor offers two FET models—Studio FET is rumored to be modeled more specifically after an 1176, and this speculation is lent some credence by the fact that the Knee control is greyed out when this model is chosen. The original’s response is, again, program-dependent, and disabling this user setting could allow the model to mimic this more precisely.

Part of the quality of compressors like the LA-2A and the 1176 comes not only from the unique response of their gain-reduction circuitry, but also from the warmer, all-tube signal path (LA-2A) vs. the somewhat edgier quality of FET designs (the 1176 and its many, many clones). Logic addresses this as well, in the hidden extra control panel, revealed with a click on the disclosure triangle at the lower left of the plug-in. 

The Logic Compressor’s Distortion options.

The Logic Compressor’s distortion options.

Here you’ll find options to add a bit of subtle, simulated overload to whichever model you choose. The choices range from from Off to Soft overload (tubes?), and Hard to Clip, which would assumedly be more appropriate with models like the FET simulations.

VCA Compression

The third compressor type is VCA. 

The Logic Compressor’s Vintage VCA Mode.

The Logic Compressor’s Vintage VCA mode.


The Logic Compressor’s Studio VCA Mode.

The Logic Compressor’s Studio VCA mode.

VCA designs are considered the standard for modern compressors. In these designs you’ll usually find a harder knee behavior, and they’re good for clamping down hard on transients, like pop and slap spikes from a bass, as well as any situation where the signal really needs to be brought under tighter control. The dbx 160, and the SSL bus compressor, are the classic designs of this type, and, once again, rumor has it that Studio VCA may be based on a particular hardware model.

The dbx 160 VCA Compressor.

The dbx 160 VCA Compressor.

Conclusion

If you want to hear the difference in response and character of these different models in the Logic Compressor, open one up, dial up a usable compression effect with the generic Platinum design, and then switch between the models—the differences may seem subtle at first, as they are with the originals, but with a little informed tweaking, you’ll be able to coax a distinctly different character out of each one, for just the right kind of compression on the various elements of a mix. 

So, if you haven’t already discovered them, go ahead and spend some time exploring the circuit options in Logic’s Compressor—you won’t be sorry you did!

Joe is a musician, engineer, and producer in NYC. Over the years, as a small studio operator and freelance engineer, he's made recordings of all types from music & album production to v/o & post. He's also taught all aspects of recording and music technology at several NY audio schools, and has been writing articles for Recording magaz... Read More

Discussion

BenB
YES! Love these LPX articles that have really useful information. I always wondered about those circuitry choices. Now it is clear, and I can really tweak out my mixes really well. GREAT article! Bravo!
Matt Denton
Somewhere around Logic Pro X 10.1 they did reskin these different circuit types with attractive faces so you can see the difference between studio and vintage, for instance, once you get away from the (underrated) Platinum circuit. Great article, thanks!
Joe A
Thanks, guys! Back before the re-skinning I'd always felt that if the Logic Compressor had a fancier graphic people wouldn't be so quick to dismiss it in favor of fancier third-party plug-ins. Now, with the new look making it clearer what circuit types are being emulated, I'm sure it gets more of the attention it deserves, even though the models are the same (except for the new dbx-style model, which is a welcome addition)..

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