Tube Versus Solid-State Compressor Basics

Compress with Finesse:
Learn to Harness Tube & Solid-State Compression

Engineers are often taught to use compression for its most obvious function — leveling dynamics, adding punch, definition, and creating a more cohesive balance between tracks. But what influences our use of compression in the first place? And why would you choose one type of compressor over another?

Here, we’ll dig into the sonic differences of legendary tube and solid-state compressors, plus give you tips for harnessing their individual strengths on your tracks.

Lessons in Compression

Beyond technicalities and feature sets, many engineers prefer to use one type of compressor over another, simply because they understand how it will respond to a given source. This type of relationship with any plug-in or piece of gear will help you make more informed decisions on-the-fly and save you valuable time.

Here, we'll focus on popular tube and solid-state compressor varieties and their basic attack and release characteristics. However, where components are concerned, note that transformers impart their own character to both tube and solid-state designs with subtle distortion and harmonics. But for the sake of this article, we will focus solely on tubes and transistors as the key components. As an additional resource and compression primer, be sure to check out the excellent article, Audio Compression Basics.

“When you want to control dynamics, but don’t want to hear the compressor ‘working,’ use optical compression.”
— W. Shanks, UA Senior Product Manager

Totally Tube

Tube compression is the “glue” that can bring tracks together and inject sources with warmth, harmonics, and timeless analog character.

Arguably the greatest vocal compressor of all time, the Teletronix LA-2A is an iconic valve compressor that revolutionized recording in the 1950s. Its unique, tube-driven electro-optical gain reduction offers a slow attack and warm sonics. Though considered relatively “tame,” and better for subtle leveling than fast dynamics control, the LA-2A is the quintessential example of tube compression, engulfing transients without strangling the source.

The UA 175B and 176 Tube Compressors lend distinctive tube flavors with a dedicated gain reduction tube rather than the optical photocell design of the LA-2A. This gives the 175B/176 units faster attack times and more aggressive character, all while maintaining the complexity and warmth of classic tube compression.

“Something unique to the 175B/176 is their broad transition between clipped and not clipped in the amplifier stage; it’s an enormous range.” — W. Shanks

While the 175B and 176 are known for imparting color, warmth, and harmonics, not all tube compressors are so character-rich. The legendary Fairchild 660 and 670 are among the most coveted compressors in the world — favored for their refined, slightly more polished response rather than edgy, tube grit.

Originally designed to help mastering engineers control dynamics before going to the cutting lathe, these 20-tube titans have a natural, fast attack that you’ve undoubtedly heard on hundreds of hit records from the heyday of classic pop, rock, and Motown. An obvious choice for the mix bus, the Fairchild is equally suitable on drums, bass, and even vocals thanks to its articulate response.

Due to the complex nature of various tube and transformer-based gain stages, valve compressors offer a wide sonic range and variety of setting-dependent textures, grit, and subtleties. They can add unmistakable coloration and punch, but also refined sheen on nearly any source.

Solid State of Mind

The advent of solid-state recording technology in the late 1960s brought about compressors with an entirely new set of sonics and behavior. These FET and VCA-based designs allowed for even faster attack times and controls not available in early tube‑based circuits.

“Compressors can be viewed either as a utilitarian tool or a creative ‘effect’. But an 1176 is unique; it could be used for function, but also creatively as a toneshaper.” — W. Shanks

Not coincidentally, it’s during this time that compression starts being used creatively as an effect to bolster tracks with color, punch, and excitement. In 1968, Bill Putnam Sr.’s vision of a compressor with exceptionally fast attack was fully realized with the release of its solid-state successor, the 1176. And in short time, studios around the world latched on to its immense potential.

The first true peak limiter to feature all-transistor circuitry, and prized for its ultra-fast FET gain reduction, the 1176 Classic Limiting Amplifier yields undeniable character — offering more gain and quicker attack. If you’ve ever wondered how it became so ubiquitous, consider its immense flexibility, in-your-face immediacy, and rock-solid reliability that works on seemingly any source.

“My dad was always looking towards a compressor with faster attack. The 1176 represents his end vision to make a studio-grade compressor with fast attack and bold sonic texture — qualities that began with the 176.”
– Bill Putnam Jr.

Like their valve counterparts, solid-state compressors impart their own special brand of color. They can be snappy and refined, and at times less colorful than their tube counterparts. For example, the VCA-based SSL 4000 G Bus Compressor is a celebrated bus compressor with loads of transparency and headroom potential, though its ability to “glue” tracks together while adding cohesiveness, punch, and definition to a mix are attributes that one might commonly associate with valve compression.

For an even more colorful example of solid state compression, look no further than the Empirical Labs EL8 Distressor. With seemingly limitless versatility — useful on anything from 808s to vocals — and loads of gritty textures on tap, the Distressor takes everything you may have thought about solid-state components and turns it on its head. It’s anything but sterile or uncolored, and massively flexible, making it a modern classic by most standards.

The EL8 Distressor offers unparalleled fast attack times and loads of color and personality.

Going Deeper With Compression

Where forum chatter is concerned, it’s easy to build walls around your concepts of solid-state and tube technology. As creatives, producers, and engineers, it’s important to enlist multiple types of compressors for different uses and to embrace the eccentricities and character of both solid-state and tube varieties. Beyond understanding the functions and technicalities of the circuits, always remember to use your ears when adopting new gear and sounds into your workflow — be bold, break limits, and enjoy the myriad of sounds and textures available to you.

— McCoy Tyler