Compressors 101: A Guide to Compression Types and When to Use Them

A compressor is an audio signal processing tool that reduces the dynamic range of an audio signal. In other words, it reduces the difference between the loudest and quietest parts of a recording.

When a compressor is applied to an audio signal, it detects when the level of the signal exceeds a certain threshold and applies gain reduction to bring down the level of the louder parts. This results in a more even and controlled sound, where quieter parts of the recording can be heard more clearly, and louder parts are prevented from overpowering the mix.

Compressors can be used for a variety of purposes in music production, such as:

1. To even out the levels of a performance, like a drum kit, where some hits are louder than others
2. To add sustain to an instrument like a guitar or a vocal
3. To bring out quieter parts of a recording, like a whisper in a vocal track
4. To prevent certain elements from overpowering the mix, like a bass guitar that is too loud compared to the rest of the mix.

Using a compressor can be a delicate balancing act, and too much compression can lead to a loss of natural dynamics and a squashed sound. In some genres that is the desired sound, but in others it might be perceived as lifeless. A skilled audio engineer will use compression judiciously and in conjunction with other tools like EQ to achieve a balanced and professional-sounding mix.

Rick Beato has made a brilliant video about compressioncalled “How The Pros Use Compression – Audio Compression Instruments and Mixes”

Here are some of the most common types of compression and terms related to them:

1. Optical Compression: This type of compression uses an optical element like a light-dependent resistor to vary the amount of gain reduction applied to the signal. Optical compressors are often used for their warm, smooth sound and subtle compression.
2. VCA Compression: VCA (Voltage Controlled Amplifier) compression is a popular type of compression that uses an amplifier with a voltage-controlled gain element to apply compression to the signal. VCA compressors are known for their fast, precise response and transparent sound.
3. FET Compression: FET (Field Effect Transistor) compressors use a transistor to vary the gain of the signal, resulting in a punchy, aggressive sound. FET compressors are often used on drums and other percussion instruments.
4. Tube Compression: Tube compressors use vacuum tubes to apply compression to the signal. Tube compressors are prized for their warm, musical sound and can add harmonic distortion to the signal, which can be desirable in certain applications.
5. Multiband Compression: Multiband compression is a type of compression that allows for different compression settings to be applied to different frequency ranges of the signal. This allows for precise control over the balance of the mix and can be useful in situations where certain frequency ranges need to be controlled more than others.
6. RMS Compression: RMS (Root Mean Square) compression is a type of compression that applies gain reduction based on the average level of the signal over time, rather than the peak level. RMS compression is often used for more subtle, transparent compression.
7. Peak Compression: Peak compression is a type of compression that applies gain reduction based on the peak level of the signal. Peak compression is often used for more aggressive, “in your face” compression.
8. Parallel Compression: Parallel compression, also known as “New York” compression, is a technique where a compressed signal is mixed with an uncompressed signal. This allows for a compressed signal to be added to the mix without losing the natural dynamics of the uncompressed signal.
9. Sidechain Compression: Sidechain compression is a technique where the compression is triggered by a separate audio signal, rather than the signal being compressed. Sidechain compression is often used in electronic music to create pumping effects and rhythmic patterns.

Each type of compression has its own unique characteristics and applications, and the choice of which type to use will depend on the specific needs of the mix and the desired sound. 

Interested in a deep dive? Read this on Wikipedia about: Dynamic Range Compression