top of page

Compressors and their types!

What is a compressor?

A compressor is a dynamic device whose main function is to reduce the strongest transients / amplitudes to bring them closer to the weakest.

However, a compressor can have other uses, like adding harmonic distortion, extending the sustain of a room etc.

There are several categories of compressors, and each has its own particularity. Today I’ll explain the 5 main types of compressors.

The Vari MU (or Delta MU, Variable Gain etc.) compressor, created in the early 1930’s mostly for radio transmission, is based on a tube gain reduction circuit. The more the tube is fed with amplitude, the more the circuit will reduce the signal.

These compressors can also be composed of a tube amplifier circuit to produce more gain. This naturally adds harmonic distortion to the signal.

The Vari MU has more controllable parameters than the Opto compressor. Most of the time we will have access to a Threshold independent of the input gain, a variable attack and release time (still slower compared to most VCAs and FETs) and an independent gain output. Its use is mainly to create a glue effect (to give coherence between instruments to make them sound together) and add harmonic content to enrich the signal. This is why they are most often found at the end of a mix bus chain or in mastering. We will end up with a smoother and "transparent" compression -> less compression artifact

Occasionally the use of a Variable Mu can add presence while applying RMS compression to the signal. This allows you to adjust the level differences during a performance. For example, a voice that is struggling to come out of the mix or a group of instruments (such as the elements of a drum kit) that create a lot of level differences during the song.

My personal choices:

  • Manley Variable Mu: Awesome as a mix bus/mastering compression

  • Fairchild 670: Efficient on drum bus, vocals, mix bus/mastering

  • Arturia Comp Tube-STA: Very good on bass, vocals, synths, define the Pop radio’s sound in the 1960’s

The Diode Bridge compressor, introduced in the 1940’s, is a very fast, non-linear compressor that adds harmonic distortion. However this compressor handles low volumes and therefore needs to amplify the output signal, which unfortunately can increase the amount of noise present in the signal.

It is one of the least used compressors, however it can be found at the end of a mix chain, on drum buses etc. It is a compressor that is considered by its nature between the VCA and the Opto.

My personal choices:

  • Neve 33609: Awesome on drum bus, mix or master bus

  • Neve 2254E: Great on dynamic vocals, synths

The Opto (optical), developed in the 1950’s, is a very slow compressor, which applies compression to the signal through a light sensitive resistor. The more you feed the circuit, the more the compression ratio increases.

Most Opto compressors have a tube amplifier circuit, adding harmonic distortion to the signal. This makes this compressor one of the least transparent. Ideal for adjusting signal levels and adding color to the signal.

My personal choices:

  • Teletronix LA-2A: Good on vocals, bass, kick and snare bus

  • Tubetech CL1B: Awesome on vocals, synths

  • Universal Audio LA-3A: Ideal for guitars

FET compressors (Field Effect Transistors), introduced by Bill Putman (Universal Audio/UREI) in 1966, are one of the fastest compressors. It uses a circuit with transistors that apply the gain reduction to the signal.

The transistors are known to produce odd order harmonics, giving a so-called more aggressive saturation.

They allow a better response to transients while keeping a certain control on the compression. Ideal on sources that have transient problems, like a snare drum that has too much attack , or a kick that doesn't "breathe". It helps to create articulation in the manipulation of the signal, while it adds punch and brightness.

My personal choices:

  • Urei/Universal Audio 1176 Rev D: Great on vocals to replace the LA-2A and adjust the levels of the track.

  • Urei/Universal Audio 1176 Rev A: Ideal to add punch during the compression, I love it on a snare that miss brightness and “snap”

  • Drawmer 1973: Very efficient on a mix or master bus, perfect on drums, this is a multiband compressor using a FET circuit.

The VCA (Voltage Controlled Amplifier), designed in 1973 by the company DBX, is the fastest and most controllable of all compressors (the most adjustable parameters available). It is ideal for fast compression and is one of the most transparent and efficient.

The VCA is very useful when you want to control fast transients without (or as little as possible) adding colorations/harmonic distortion. Some units are meant to add some harmonic content while applying the compression. Can be defined as one of the most aggressive compressor.

Very efficient on vocals when we need to adjust the peaks of a performance, on an acoustic guitar to control the dynamic or as a “Glue” compressor to create coherence between individual tracks.

My personal choices:

  • API 2500: Tight and punchy, awesome on drum bus, mix or master bus and vocals

  • SSL G bus: THE glue compressor, great on mix bus and drum bus, as well as for acoustic guitars

  • DBX 160: “THE ref” for any applications

  • Bettermaker Mastering Compressor: A very versatile type of compressor for mastering.

10 views0 comments

Recent Posts

See All


bottom of page