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Compression is a type of dynamic range processing that closes the gap between the loudest and quietest parts of a track. It adjusts a signal’s level based on its amplitude; in other words, how loud it is at any moment. It does not, however, just make audio louder. It makes it more consistent.
A compressor monitors the audio constantly. It reduces gain when the level goes over a threshold. The settings the producer or engineer chooses decide how much gain it reduces and how quickly.
In short, a compressor’s primary job is reducing loud peaks. It makes things quieter first. Makeup gain then brings the level back up. The result is a narrower dynamic range: a smaller difference between the loudest and quietest moments in the audio.
Key Takeaways
- Compression is a dynamic process tool that decreases dynamic range (the difference between an audio signal’s loudest and quietest part).
- When a threshold is exceeded, the compressor reduces the signal level. It stops when the level drops back down again to a point below the threshold.
- The four most important controls on a compressor are: threshold, ratio, attack, and release.
- Producers use compressors to smooth out uneven performances.
- Overuse a compressor, and you risk flattening the music and making it sound lifeless.
What Is Audio Compression?
Audio compression is a tool that reduces what’s called the dynamic range of a sound. Dynamic range is the difference between the softest part of an audio signal and the loudest. For example, you can imagine the volume differences between a vocal take that includes both a whisper and a shout.
The compression process all starts with a defined threshold. When any part of the input signal rises above that threshold, the compressor turns it down. How much it turns it down by depends on the ratio. At a 4:1 ratio, for example, a sound that goes 8 dB over the threshold comes out only 2 dB over. The signal is reduced, but it usually stays above the threshold. Only very high ratios keep the signal at or near the threshold. If a sound is below the threshold, it isn’t changed.
The idea is to decrease the dynamic range so the loud and quiet sections are more similar in volume.
Why? Because a smaller dynamic range makes mixing a little easier. The levels are more even from one moment to the next.
What Does a Compressor Do in Music?
In music, a compressor lowers the volume or level of sound when it’s louder than the predetermined thresholds. It monitors the signal constantly, so it can apply gain reduction whenever needed. Here’s how the process unfolds:- First, audio enters the compressor.
- Let’s say a signal crosses the threshold.
- The compressor applies gain reduction.
- The signal is brought down so it’s below the threshold.
- The compressor releases and stops attenuating the signal.
- Makeup gain can restore the overall level, if needed.
- Individual tracks (vocals, drums, bass, and guitar)
- Instrument groups
- The mix bus
How Does a Compressor Work?
A compressor’s controls shape when compression begins, how strongly it acts, and how quickly it responds. Threshold and knee determine the starting point, while ratio sets the intensity. Attack and release establish the timing and makeup gain restores the level afterward. Let’s take a closer look.Threshold
The threshold is the level, in decibels (dB), at which gain reduction begins.- Below the threshold, no gain reduction is applied.
- Above the threshold, gain reduction begins.
Ratio
The ratio determines how much the compressor reduces the signal above the threshold. A 4:1 ratio reduces a 4 dB overshoot to just 1 dB above the threshold. A 2:1 ratio reduces the same overshoot to 2 dB. Low ratios (2:1) produce subtle gain reduction. High ratios (8:1 and above) have a greater effect on loud peaks.Attack
How quickly the compressor begins to reduce gain after the signal crosses the threshold is called attack. The attack time changes how the start of each sound comes through. For example:- Fast attack catches the initial transients and controls them.
- Slow attack lets more of the first hit through before gain reduction begins.
Release
Release is the speed at which the compressor lets go as the signal falls back below the threshold. It interacts closely with the rhythm and tempo of the music. If the release is too fast, the level will bounce. A slow release holds the signal down for too long and masks the following note. Both can produce audible pumping, an unnatural rise and fall in volume. Setting attack and release times properly demands precise listening skills.Knee
The knee is a control that determines how gradually the gain reduction is applied as a sound nears the threshold.- A hard knee reduces the gain as soon as the signal is above the threshold. It’s harsh.
- A soft knee applies gain reduction gradually as the signal nears closer to the threshold. It’s softer and more subtle, and results in a smoother blend.
Makeup Gain
A compressor lowers the overall level; makeup gain brings back the loudness afterward. Makeup gain is a separate volume control, and it plays no part in reducing dynamic range. Our ears typically prefer the louder version of a sound. So, as you evaluate compressed versus uncompressed audio, first make sure their loudness is the same. This level-matched A/B comparison is a good way to find out whether the compressor made the sound better or just made it seem louder.Why Is Compression Used in Music?
Compression is used in music to create a more even sound with greater volume consistency. It smooths dynamics and tames transients.
Here’s a closer look at how producers use it.
Control Dynamic Range
When a singer sings, the volume of their voice goes up and down naturally. In some cases, a word or syllable jumps out of the mix, which may not sound ideal. A compressor smooths out those kinds of variations.
Add Punch and Control Transients
At the start of a sound, there’s a sharp spike. This is called a transient. An example is the smack of a drumstick.
You might want to keep these in. With the right attack and release settings, a compressor leaves the transient untouched before reducing the level of what comes after. This creates a punchy, powerful effect.
A faster attack does the reverse; it softens the impact.
Help Instruments Blend in the Mix
Sudden peaks or loud sections bring an instrument to the forefront of the track. When they soften, the instrument fades back again. You can control those peaks so that each element of the track (like the bass, vocals, and so on) is more stable and balanced. You can hear each part.
Creative Effects
Compressors are creative tools as well:
- Parallel compression. You combine a squashed, compressed version of a sound with the original. This parallel processing adds energy.
- Sidechain compression. The compressor reacts to a different sound. In EDM, producers use sidechaining to make a synth dip every time the kick drum hits. The Ableton Live manual covers sidechain routing for its compressor device.
- Intentional pumping. A fast-reacting compressor with a beat-timed release makes the whole track breathe in and out. Producers in techno and house sometimes set up the release so the level recovers right before the next kick.
That’s why a compressor works as both a corrective tool and a creative one.
Compression Examples: Vocals, Drums, and Bass
Here’s what a compressor does on three instruments:
- Vocals. If you write a song and record your own vocals, using a compressor is an option. It may help the vocal remain present and easy to follow.
- Drums. A compressor can tame a spiky snare or make a kick hit harder.
- Bass. Some bass notes ring out louder than others. A compressor makes the low end solid and even.
- Guitars and the mix bus. In the studio, a compressor can sustain a guitar’s sound. Light mix-bus gain reduction glues the parts together before you master the track.
There are no perfect or one-size-fits-all settings. They depend on the recording, the performance, genre, tempo, and the sound you’re hoping to achieve. Have fun and experiment.
What Does Compression Sound Like?
A compressor isn’t quite as noticeable as things like reverb, delay, or distortion in music. Instead, it’s a little more subtle.
When you next listen to a track, see if you can hear how a compressor:
- Reduces the dynamic range (or the volume differences) between loud and soft moments
- Smooths performances and control peaks
- Affects the punch of each hit of a drum
- Increases sustain so notes ring out a bit longer
- Causes audible pumping with aggressive settings
Try playing the same clip before and after the compressor. Adjust the levels so both versions sound equally loud; that way, you’re comparing the effect of the compression rather than a difference in volume.
A drum loop or vocal tracks are good ones to try. See if you can detect and describe the changes. With a bit of practice, you’ll notice compressors on the songs you listen to every day.
Common Compression Mistakes
If you’re a beginner using compressors, try not to make these all-too-common mistakes:
- Overcompressing everything. Some tracks don’t need a compressor at all.
- Using too much gain reduction. Large amounts of gain reduction remove the natural dynamics of a performance. The result can sound flat.
- Setting attack and release by the numbers. Settings copied from a chart ignore the unique sound you’re working with. Tweak them by ear for each source.
- Confusing louder with better. Raising the makeup gain can make the compressed version seem better only because it’s louder.
- Compressing when volume automation would work better. A few extreme peaks or uneven phrases are easier to fix by hand. Lower their levels with volume automation first; introduce a compressor only if 100% necessary.
As a rule of thumb, use a compressor with a purpose in mind, whether that’s fixing a specific problem or creating a deliberate effect
FAQs About Compression in Music
What are the four types of compressors?
The four major types of analog compressors are:
- VCA
- FET
- Optical
- Variable mu (tube)
These designs respond at a unique rate and have their own character.
Does every track need compression?
Not at all. Some tracks don’t need compression. If a signal is even and controlled already, there’s no need to use a compressor. Only give one a go if you are trying to solve a specific problem or want to create an effect.
What is the difference between compression and limiting?
The difference between compression and limiting is the intensity of the gain reduction. A limiter is a compressor with a high ratio (around 20:1 or higher) and a fast attack.
What songs use compression?
All kinds of songs use compression. In fact, most of the commercial recordings you hear have used compression at some point during tracking, mixing, or mastering.
In pop music, vocals are compressed to allow the listener to hear every word above the beat. In rock and hip-hop, compressors are used in much the same way.
Which audio compression is best?
There’s no one best audio compression type. It all depends on the recording and the kind of sound you’ve set out to achieve. Not sure where to start? Try an optical compressor for vocals. VCA compressors are a popular choice for the mix bus as well.
Conclusion
So, that’s compression in music. It’s a tool that controls the dynamic range of an audio track, which helps sounds blend together in a mix. It leverages a mix of approaches, including threshold, ratio, attack, release, knee, and makeup gain.
There’s no single perfect setting for compression. If you want to get started, decide on the right settings for your track specifically.
And finally, the best way to learn how to best use compression in music is to experiment. Make changes to one control at a time and listen carefully to the result that comes out the other side. Let your ears be the ultimate judge. In time, you’ll know exactly what each control does and how to use it to achieve your sound goals.
