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CLA-2A vs. CLA-3A: Classic Compressor Match-Up

May 12, 2021

The LA-2A and LA-3A are two of the most famous compressors of all time and have long been favorites for vocals, bass and other instruments. See our comparison between the tube and solid-state models and learn how to best use them for your tracks.

By Craig Anderton

CLA-2A vs. CLA-3A: Classic Compressor Match-Up

The LA-2A (CLA-2A) is one of the most well-known, coveted and popular hardware compressors ever made. Its successor, the LA-3A (CLA-3A), never achieved quite the same cachet; perhaps this was because people were taken aback that the LA-3A didn’t sound quite like the LA-2A. Regardless, those engineers who checked out the LA-3A in-depth appreciated its unique attributes. “Different” didn’t mean better or worse—it simply meant it was up to the engineer to use the right tool for the job.

Superficially, the two compressors have more similarities than differences. Consider the gloriously simple user interface: peak reduction sets the amount of compression applied and gain determines the output level. You can also choose compress (low ratio) or limit (high ratio) modes—and don’t ignore the limiting mode just because these units are best-known as compressors. The remaining user-adjustable control varies the response from flat compression over the entire frequency range, to more compression at higher frequencies. Although some treat this as a primitive de-esser, it can also push a sound further back in a mix by reducing apparent brightness.

CLA-2A Compressor / Limiter
CLA-3A Compressor / Limiter

The user interface for both of these classic compressors, the CLA-2A and CLA-3A, is a paragon of simplicity.

Both the CLA-2A and CLA-3A plugins include an “analog” option to emulate the noise floor and hum (50 or 60 Hz) from the original hardware units. I prefer no hum, but this option does give a more “vintage” sound for those who consider hardware imperfections essential to a unit’s character.

The Opto Factor

A compressor’s primary, distinguishing characteristic is the technology used to compress the signal. Both the LA-2A and LA-3A hardware units are based on the T4 opto-isolator, which combines a photo-resistor and electro-luminescent panel. Audio driving the panel changes the amount of light that shines on the photo-resistor, which alters the level and therefore, the gain. The opto-isolator’s inherent response is a “happy accident” for audio—it’s almost as if it comes with a built-in auto-attack/release switch. The fixed, non-linear attack doesn’t remove all the punch, and the release occurs in two stages, where the release time decelerates over time. (Even some modern hardware designs that use LEDs instead of electro-luminescent panels have a similar response.) Note that a major CLA-2A and CLA-3A advantage over the hardware is that their virtual electro-luminescent panels don’t deteriorate over time.

However, the two hardware compressors don’t drive the electro-luminescent panel in the same way so their attack/release characteristics are different. With higher-level transients, the LA-3A can react more quickly because its circuitry lights up the electro-luminescent panel more rapidly than the LA-2A (after the initial transient, the response is more alike). The CLA-2A and CLA-3A model this difference, which you’ll hear if you A-B the two compressors on drums and add heavy compression. The drums will sound tighter, punchier and sharper with the CLA-3A. Transients with the CLA-2A will sound less distinct, and the release will reduce punch somewhat; however, the sound will be warmer and sometimes fatter as well.

These same characteristics explain why many engineers prefer the CLA-2A’s smoothing effect on vocals. The fixed attack is long enough to let consonants through, so while the vocals retain clarity, the peaks and valleys are smoother. Others prefer the CLA-3A for vocals that need a lot of compression because that much compression with the CLA-2A would sound more “processed.”

Although the release characteristics do seem to have an uncanny, program-dependent ability to produce the right release at the right time, there are a couple of fine points. With strong signals where the release lasts longer, the release time may not go back to its quiescent state before the compressor gets hit again with signal, so the attack time will be shorter than expected. Conversely, if the release does play out all the way, then there will be the full attack time when the next audio hits.

The Tube Difference

There’s also a sonic difference between the LA-2A’s tube-based circuitry and the LA-3A’s solid-state design. Tube-based circuitry colors the sound more than solid-state due to a variety of factors, one of which is the Miller effect. This limits gain at high frequencies and is most pronounced in triode tubes (the LA-2A used dual triode tubes) compared to solid-state circuitry. The CLA-3A has an overall less colored sound than the CLA-2A, but of course, choose the appropriate tool for the scenario. Also note that the higher the CLA-2A’s gain, the more it takes advantage of the sound of running the source through a tube.

Joe Chiccarelli would use the LA-2A (CLA-2A) on Jack White’s vocals when mixing the White Stripes to take advantage of the tube distortion on the output stage.

When Do I Use What?

If your audio doesn’t have high-level transients or need a fast compressor response, then it might benefit from the CLA-2A’s warmth and smooth compression action. The CLA-3A won’t give the same kind of warmth but will provide a tighter, punchier sound—especially in the midrange frequencies inhabited by guitars, rotating speaker cabinets, electric pianos and the like.

However, there’s no one-size-fits-all solution, and electric bass underscores that. Some swear by the CLA-2A while others swear by the CLA-3A, and... they’re both right. For a smoother, warmer bass, the CLA-2A usually gets the nod. For a cleaner, tighter sound with more punch, the CLA-3A is more appropriate. This is also why some engineers prefer the CLA-3A for electric guitar and male vocals—you don’t necessarily want those sounds to be “smooth.” (If you play electric guitar, you’ll know what I mean when I say the CLA-2A is like nickel strings, while the CLA-3A is more like stainless steel strings.)

Similarly, overhead mics have partisans for both compressor types. Those who want the overheads to blend in with the drums may try the CLA-2A first. Those who want the overheads to supplement the drums will likely go for the CLA-3A.

Consider acoustic guitar. Do you want the articulation and string attack to stand out in the mix? The CLA-3A will preserve that articulation and focus the midrange frequencies. If you prefer to have the acoustic strumming in the background, then the CLA-2A will probably be the right choice.

Additionally, the CLA-2A and CLA-3A complement each other well. Many engineers recognize the value of using two compressors in series, whether to obtain gentler compression effects by setting each for very subtle compression or to exploit the different characteristics of two compressors. For vocals, try the CLA-2A for some gentle warmth and smoothness, then compress that with a CLA-3A to give the vocals punch in a mix. Some do the reverse; tame the vocal with the CLA-3A, then add warmth with the CLA-2A.

Overall, you’ll notice that the differences between these two compressors aren’t really all that subtle—when you experiment with them on different signal sources, after a couple of A-B comparisons your ears will have no problem telling you which is the right choice.

Want more on different types of compressors? Check out which compressor sounds best on the mix bus in this shootout.

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