The typical controls on a compressor can be confusing and often misunderstood. At the heart of the MXR Studio Compressor is the ratio control, which offers up four levels of squish.
I was recently listening to three accomplished guitar players discuss the how, when, and where to use compressors in their guitar rigs. All three players had wildly different views on all aspects of compressordom, from where they should be used in a signal chain to whether they are even worth the hardware that holds them together.
Their conversation made me reflect on compressors more generally, and their standing as probably the least understood guitar pedal effect. There is a long-running joke about the guitar player who spends 30 minutes dialing in his compressor before the sudden realization that, for all the knob twisting, the pedal itself has never turned on. Most players have put on the compressor dunce cap for at least 30 seconds—if not 30 minutes.
When compared to effects like distortion and delay, compression can be as esoteric, nuanced, and arcane as a clandestine funk-guitar society’s secret handshake. In my experience, a large swath of guitar players cannot even detect compression until they are sonically beaten over the head with it. And of those who can discern the bludgeoning, many don’t know which knob to turn to achieve a more subtle effect. We guitar players should have known we were in trouble when many professional compressors came with buttons labeled “auto.” If even our know-it-all, front-of-house cousins need a crutch, what hope do we have?
Compression originated in the recording studio, where professional engineers were both its inventors and primary users, so its controls tend to be more technical than your amp’s bass, middle, and treble knobs. Let’s break down some controls in the simplest terms possible.
Introduced in 1972, the Dyna Comp had two simple controls: output and sensitivity. It’s far from transparent, but added a musical coloration that made fans out of Bonnie Raitt and Lowell George.
Threshold: This setting determines what gets squished and what doesn’t. Everything below the threshold passes through unchanged. Everything above the threshold gets squished. This is often labeled “sustain” on many guitar pedals. Sometimes, as the sustain is turned up, the compressor’s threshold point goes down, lowering the bar for what gets compressed, and more effect gets applied to your dry signal.
Ratio: How much compression is applied to signals above the threshold. A 1:1 ratio would mean no compression. At 2:1, for every 2 dB over the threshold, the compressor will only let 1 dB through. Some classic compressors have a ratio around 30:1. This means that above the threshold, you can increase the input signal significantly but receive only a small increase in output. Boom, you’re chickin’ pickin’.
Attack: This adjusts how fast it takes the compressor to get to work. A shorter attack means the clamping action happens immediately, while a longer attack time lets a brief burst of signal through before they start applying the aforementioned compression ratio.
Release: After the signal drops below the threshold, the compressor takes a certain amount of time to stop compressing or release. A longer release lazily hangs on and stops compressing when it gets around to it. Shorter releases get out of the way faster, and the next transient can get through uncompressed before being re-attacked.
Makeup Gain (or Output Level): The compression process naturally limits gain. To match the energy level of your uncompressed signal, you may need to boost the compressor’s output. Compression evens out the peaks, and makeup gain can compensate for any perceived differences in level.
Threshold and ratio are the heart of the compressor’s function. Threshold decides what gets compressed and ratio determines how much it’s compressed. Attack and release are about how fast compression is applied and how quickly it stops being applied. By controlling these, you are controlling how quickly transients are attacked and how slowly transients are released. Every guitar compressor has an attack and release time, but many designs hide these controls via internal, fixed component values. The designer has benevolently dictated what setting you should use. Output level lets you make up for all that crushing by adding level to compensate.
This is just the beginning of compression. We’ve got the knobs, we know the function, and next time we’ll discuss how we can use this dynamic darling
