Whether you like country, hard rock, funk or metal, chances are a compressor pedal was used.
A compressor pedal makes the life of a guitarist just that little bit easier. The notes come off your fretboard a bit easier, you have more sustain and it all sounds a bit fatter than without a compressor. But what does a compressor pedal actually do? and what are the differences? In this article I explain how a compressor pedal works and which different types there are.
What is a compressor pedal?
To start with the main question, what exactly is a compressor pedal? A compressor pedal controls the dynamic range of your instrument. Hard notes get softer and soft notes get louder. A compressor pedal protects against excessive peaks in your signal and ‘smothers your sound a bit more’. As it were, it glues different notes together, often making it sound just a bit better. It sounds more ‘produced’ and sometimes more professional with a compressor pedal. But you also sacrifice something for this, namely the dynamics of your playing.
What can you do with a compressor pedal?
With a compressor you get less dynamics and more volume without your guitar going overdrive. If your (bass) guitar is lost in the mix, a compressor can offer a solution to become more audible. A compressor works just a little more subtly than increasing the volume on your amplifier or guitar. Furthermore, a compressor helps guitarists to play nice funk rhythm guitar parts. You create a sticky sound with it that also sounds very even. Also with country music you often hear a compressor in combination with a Fender Telecaster. Which chicken pickin’ part is actually played without compression? Finally, compression also adds sustain, which is very useful for solos, for example.
How does a compressor pedal work?
Virtually every compressor works the same way. You set a certain threshold volume. If your signal exceeds this threshold, the compressor will kick in. Depending on the settings on your pedal, this happens quickly or slowly and at a certain value and for a certain period of time. The most commonly used buttons/settings you will encounter on guitar compressor pedals are listed below.
Ratio – Sets the amount by which you attenuate your signal. Common settings are 2:1, 4:1, 8:1 etc. For example, 2:1 means that if your signal goes above the threshold by 8 dB, it will be reduced to 4 dB above the threshold. A ratio of 4:1 in this case means that your signal is even more 2 dB above the threshold. Some pedals have an infinity setting, with which you set that your signal should not exceed the threshold. This is the setting that limiters use by default.
Threshold – With the threshold control you set the volume level that forms the threshold for the compressor. Above this threshold the compressor will operate, below it not. You won’t find a threshold button on many guitar pedals. Often this is already set by the manufacturer and cannot be adjusted. By boosting the volume that goes into the pedal, you can still ‘check’ it.
Attack – The Attack knob controls how quickly the compressor responds to your signal. If you want to make sure the start of your note, the transient, doesn’t rise above the threshold, set a fast attack (knob all the way to the left). For guitar, a slow attack often sounds slightly better because it does not lose the dynamics of the attack.
Release – With the release button you control how long the compressor continues to work. A long release provides extra sustain in your sound, a short release time provides a more ‘pumping’ effect.
Sustain – Many modern compressor pedals have a sustain button. In most cases, this controls how hard the compressor works to keep the signal within the threshold. With this you can let your notes resound for a long time, but you also increase the noise level. Sometimes you also set the ratio with it (Keeley Compressor Plus)
Blend / Mix – Parallel compressors have a blend button on the pedal. A parallel compressor splits the incoming signal into 2’s. One part goes directly to the output and the other part goes through compressor. With the blend button you mix the processed signal with the unprocessed signal.
Level / Volume – With the level knob you set the output volume level. The compression makes the guitar signal softer and you can adjust it with the level knob. Very occasionally you will come across a ‘make-up gain’ button, which is the same.
Soft knee / Hard knee – With the more luxurious pedals you sometimes come across a switch with which you set the ‘knee’. A soft knee means that there is a smooth transition from the signal to the compressor. With a hard knee, this transition is immediate.
What types of compressors are there and what are the differences?
Broadly speaking, there are four different main types of analog compression. Each strain has its own sound and characteristics.
Optical compression
An optical compressor converts audio signal into light (with a light or LED) and a sensor registers the intensity of that light. The louder the guitar signal, the brighter the light, and the brighter the light, the more the gain is reduced. Optical compression is often described as musical, transparent and natural and it usually has a somewhat slower response than other methods. This keeps the attack of your signal well defined even at relatively high compression levels. A few well-known optical compressor pedals are the Strymon OB1 and Electro Harmonix White Finger.
FET (Field Effect Transistor) compression
In a FET compressor, the audio signal passes through a transistor circuit. Transistors have about the same effect as old-fashioned tubes. This type of compression is naturally snappy, has a very fast attack and a lot of focus. FET compression also adds some color to your signal which is less transparent than other shapes. A well-known compressor pedal in this category is the Origin Effects Cali 76.
VCA (Voltage Controlled Amplifier) compression
A voltage controlled compressor uses control voltage to control the amount of your guitar signal. The higher the control voltage, the more signal is transmitted. At a certain voltage level, the entire signal is allowed to pass. Voltage controlled compressors are reliable compressors with a fast attack. VCAs often give slightly less coloration compared to optical compressors. In addition, they have the highest possible compression settings and sound transparent. The Strymon Compadre is a pedal based on VCA compression.
OTA (Operational Transconductance Amplifier) compression
An OTA compressor is similar in operation to a VCA, except that the output is a variable current and not a voltage. This type of compression is by far the most commonly used in guitar pedals. It is not as fast as VCA but faster than optical compression. Well-known guitar pedals in this category are Wampler EGO, Xotic SP, Keeley Compressor Plus and the EHX Tone Corset.
Where in your effect chain do you connect a compressor pedal?
If you have decided to purchase a compressor pedal, or if you already had one lying around, the next question is where in your signal chain you connect the pedal. In this article about the order of guitar effects I explain how to connect your pedals in general. A compressor pedal is usually placed at the beginning of your signal chain, just before or after your gain pedals. If you connect the pedal in front of your gain pedals, you ensure that a limited dynamic signal goes to your overdrives. Connecting pedal after gain pedals maximizes the dynamics of your drives and compresses the overdriven signal. There is no right or wrong way to do it, so I advise you to try both.
What else should you pay attention to?
Each compressor will amplify the noise level in some way. No matter how quiet the pedal itself is, the signal going into the pedal will almost always contain some noise. This noise is further increased by compression. That shouldn’t be a problem, but it’s something to keep in mind.
Bass guitar and compression is a happy marriage
Compression is also a very useful tool for bass players in the studio and on stage. It helps to give the very lowest notes more articulation and definition. Furthermore, it also tames the loud volume peaks in the signal. Compression makes the short notes more punchy and the longer notes get a little more sustain. Your playing will become smoother and perhaps a bit easier.
Popular compressor pedals
There are now dozens of compressor pedals on the market. Every reputable brand sells one or even several. Most pedals are based on the OTA circuit. Two popular pedals in this category from Keeley are the Compressor Plus and the Compressor Pro and for bass players the Bassist Limiting Amplifier. Wampler has the Ego and a smaller version of this pedal , the mini Ego. Xotic has a popular and bestselling compressor in its arsenal, the SP Compressor. Electro Harmonix has a number of them, both for guitarists and bassists. For guitar include the Tone Corset, Platform and White Finger and for bass guitar the Nano Bass Preacher. JHS has the Pulp N Peel V4, Walrus Audio has the Deep Six Compressor V3 and JAM pedals the Dyna-ssoR.