What are the types of compressor effects? | The Basics

THE GIST

There are six different types of compressor effects—optical, VCA, FET, Valve, Multi-Band, and Parallel—each with its own unique list of attributes prioritizing different things. One basic rule of thumb with all types of compression: If you can hear it, you’re using too much.

What is an optical compressor?

These use an optical isolator circuit made up of a light bulb or LED and a photocell. The light source glows brighter or dimmer depending on the input level. The photocell reads the varying brightness of the light source and changes gain accordingly. The response time of the optical compressor is slower than other types, but I’ve found them to be very natural-sounding, with a smooth attack and release that’s hardly noticeable unless pushed hard.

Examples: Diamond CPR-1 Compressor, EHX White Finger


What is a VCA compressor?

Probably the most common type of compressor is the VCA (Voltage Controlled Amplifier). These are super versatile and can respond to the toughest, most specific conditions needed. A VCA compressor uses an integrated circuit (IC) to give precise control over gain reduction. These are usually less colored and have very little distortion, making them one of the most popular compressor types on the market.

Examples: T-Rex NeoComp


What is a FET compressor?

FET compressors use their namesake field effect transistors to emulate tubes with more reliability. They tend to have a unique sound that is fast and clean. There really aren’t many of them out there due to the extra circuitry needed.

Examples: Origin Cali76


What is a Valve compressor?

Valve compressors are sort of a misnomer in that they do not use a tube for compression. Most valve compressors are based on one of the above circuits with a tube or tubes in the signal path for a warmer, creamier tone.

Examples: Electro-Harmonix Black Finger


What is a Multi-Band compressor?

While not normally associated with pedal-based compressors, the multi-band is nevertheless worth mentioning. A multi-band compressor is exactly what it sounds like—a compressor that works differently on different frequency bands. This allows one to dial in more or less compression on the lows than the highs, or vice versa, by frequency.

The advantage is that compression artifacts on certain frequencies can be dialed out by reducing or increasing the amount of compression in that frequency band. They work by splitting the input through several filters. Each signal is then fed through its own compressor and recombined at the end. These will mostly be found in mastering suites and DAW plugins.


What is a Parallel compressor?

Parallel compression has become more popular in the guitar effects industry over the last few years. Parallel compression involves the dry signal being run in parallel with the compressed signal. The two signals are then blended back together via a Blend knob. This allows the user to dial in the amount of compression wanted and then balance it with the dry signal, eliminating unwanted artifacts from the compression.

A great application of this is when a guitarist wants to increase sustain. Since the amount of compression needed to get large increases in sustain is pretty large in itself, the resulting artifact can be “squashed" attack, where the initial attack of the note is noticeably lower in level than the sustained note. By blending in the dry signal, the initial attack can be retained with all the sweet, singing sustain coming in behind it and blending perfectly.

Examples: Barber Tone Press

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