A compressor can seem daunting, but it’s a powerful tool in any audio engineer or musician’s arsenal. By understanding the different types of compressor plugins, their applications, and their creative uses, you can elevate your mixes and recordings to new levels of clarity, punch, and cohesion.
What Is A Compressor?
A compressor is a dynamics processor that smoothens the loudness variations in an audio signal. Imagine you’re driving on a bumpy road with dramatic highs and lows. A compressor is like a skilled engineer smoothing out the terrain. It lowers the signal level when it exceeds a certain threshold.
A compressor can benefit your audio in several ways:
- Increased Perceived Loudness
Our ears perceive longer/constant sounds as louder than short peaks, even if a meter would show that the peak had a high decibel value. So, a compressed track sounds louder overall because a compressor evens out the dynamics without clipping or distortion. - Enhanced Clarity and Punch
Bringing out quieter elements can add detail and nuance while emphasizing transients, which adds punch and attack to instruments like drums and guitars. Likewise, using a compressor on vocals helps it cut through the mix easily. - Improved Mix Cohesion
Compression can help glue instruments together, creating a more unified and polished soundscape. When different instruments seem to “breathe” together due to grouped compression, it makes them sound well together. This “group” is called a bus in audio terms. - Taming Unwanted Peaks
Harsh sibilance or overly loud transients can be tamed with precise compression, resulting in a smoother listening experience.
How To Use A Compressor?
You can use a compressor by understanding it. The threshold controls how loud the signal should be for the compressor to work, whereas attack and release adjust its reaction speed. Finally, the ratio controls the compression strength, where 2:1 is lower, and 4:1 is higher.
Let’s go over the parameters in greater detail:
Threshold
The threshold is a parameter that controls when the compressor starts to work. It is the level of the input signal that triggers the compression. Any signal below the threshold is unaffected, while the compressor reduces any signal above the threshold.
The threshold is usually measured in decibels (dB) and can be adjusted to suit different types of signals and compression effects. For example, a low threshold will apply compression to more of the signal, resulting in a more consistent and controlled sound. A high threshold will apply compression only to the loudest parts of the signal, preserving more of the natural dynamics and transients.
Ratio
The ratio in a compressor is a parameter that controls how much the compressor reduces the dynamic range of a signal. It is expressed as a ratio of input level to output level, such as 2:1 or 10:1. A higher ratio means more compression, while a lower ratio means less compression.
For example, a 2:1 ratio means that for every 2 dB of the signal above the threshold, the compressor will only let 1 dB through. A 10:1 ratio means that for every 10 dB of the signal above the threshold, the compressor will only let 1 dB through.
The ratio of a compressor affects the sound quality and character of the signal. A higher ratio can make the signal sound more consistent, controlled, and punchy but also more processed and unnatural. A lower ratio can preserve more of the natural dynamics and transients of the signal but also allow more peaks and valleys in the volume. The optimal ratio depends on the type of signal, the musical genre, and the desired effect.
Some common starting points for the ratio of a compressor are:
- Vocals: 2:1 to 4:1
- Drums: 4:1 to 10:1
- Bass: 4:1 to 8:1
- Guitars: 2:1 to 6:1
- Piano: 2:1 to 4:1
- Master bus: 1.5:1 to 2:1
Of course, these are only general guidelines, and you should always use your ears and adjust the ratio according to the specific situation and your personal preference.
Attack & Release
The attack and release settings control how fast the compressor reacts to the input signal. The attack setting determines how long it takes for the compressor to start reducing the gain after the signal crosses the threshold. A fast attack (like 5 ms) grabs hold of transients instantly. It can make the signal sound more consistent and controlled but also more processed and unnatural. A slow attack (70 ms) lets transients breathe before squeezing them. It can preserve more of the natural dynamics and transients of the signal but also allow more peaks and valleys in the volume.
The release setting determines how long the compression “hangs on” after a peak. It adjusts how long it takes for the compressor to stop reducing the gain and return to the normal level after the signal falls below the threshold. A fast release (like 10 ms) can make the signal sound more punchy and exciting but might result in distortion. A slow release (150 ms) can make the signal sound smoother and natural.
The optimal attack and release settings depend on the type of signal, the musical genre, and the desired effect. However, here are some starting points you can try:
| Instrument | Attack (ms) | Release (ms) | Comments |
|---|---|---|---|
| Vocals (Pop) | 10-30 | 75 | Preserve transients and control the dynamics. |
| Vocals (Rap) | 0.1-10 | 100-200 | Sound powerful and confident. Cut through the mix. |
| Vocals (Rock) | 0.1-10 | 100-300 | Increase aggression and give an upfront sound. |
| Drums | 0.1-10 | 10-50 | Catch fast transients and add snap. |
| Snare (Ballad) | 20-30 | 40-100 | For the classic sustained snare. Use with room mic/reverb. |
| Bass | 10-40 | 80 | Use a slower attack to retain the punchiness and faster to catch pick noise. |
| Guitars | 10-30 | 100-300 | Enhance smoothness and add body. |
| Piano | 15 | 100-200 | Add depth while increasing the balance. |
| Master Bus | 30 | 300 | Glue compression to make the mix sound cohesive. |
Makeup Gain
The makeup gain of a compressor is a parameter that controls the output level of the compressed signal. It is used to compensate for the volume loss that occurs when the compressor reduces the signal’s dynamic range. By adjusting the makeup gain, you can match the output level of the compressor to the input level or increase it to achieve a louder and more consistent sound.
Some compressors offer an automatic makeup gain feature. This feature first compares the input and output levels. Then, it adjusts the output volume to match the input level. Or, it might use the compression amount to adjust the output level.
Knee
The knee parameter controls how drastically a compressor will start reducing the gain after the signal reaches the threshold level.
A hard knee means that the compressor will start reducing the gain immediately and at the full ratio value as soon as the signal crosses the threshold. This results in a more abrupt and noticeable compression effect.
A soft knee means that the compressor will start reducing the gain gradually and at a lower ratio value before the signal reaches the threshold and will not reach the full ratio value until a point past the threshold. This results in a smoother and more transparent compression effect.
The knee parameter is usually measured in decibels (dB) and can be adjusted to suit different types of signals and compression effects. A lower dB value means a harder knee, while a higher dB value means a softer knee.
Types of Compressors
A compressor shapes the tone and character of a signal depending on how it is designed and, in hardware plugins, what components it uses. Hence, there are different types of compressors, each with its advantages and disadvantages. Some of the most common types of compressors are:
FET Compressor
These compressors use a field effect transistor (FET) as the gain control element. They are fast and aggressive but musical. So, they add punch, presence, and saturation to a signal. They are great for vocals, drums, guitars, and bass. Some examples of FET compressor plugins are UAD 1176 and Softube FET Compressor.
VCA Compressor
These compressors use a voltage-controlled amplifier (VCA) as the gain control element. They are versatile and flexible, with many parameters and modes. Furthermore, they can be smooth and transparent or punchy and colorful. They are great for drums, buses, and mastering. A hardware example of a VCA compressor is the SSL G-Master Buss Compressor, and the IK Multimedia Bus Compressor is an excellent emulation I recommend.
Optical Compressor
These compressors use a light-dependent resistor (LDR) and a light source as the gain control element. They are smooth and musical, with a natural and gentle response. I often use them to add warmth, glue, and smoothness to a signal. They work great for vocals, bass, guitars, and buses. Some emulation examples of optical compressor plugins are Universal Audio LA-2A, UVI Opal, and IK Multimedia White 2A.
Variable-mu Compressor
These compressors use a variable-mu tube as the gain control element. They are warm and rich, with a soft and smooth response. They can add depth, glue, and harmonics to a signal. Hence, they are great for vocals, buses, and mastering. A famous variable-mu compressor is the Fairchild 670. Some examples of emulations are UAD Fairchild 670, Klanghelm MJUC, and IK Multimedia Dyna-Mu.
Digital Compressors
These compressors are designed to offer more flexibility and precision. They might sport features such as lookahead, sidechain, parallel, and multiband compression. Depending on the settings and mode, they can be used for any audio signal and purpose. Some examples of digital compressor plugins are iZotope Ozone Dynamics, Fabfilter Pro-C 2, and Xfer OTT.
When Should I Use A Compressor?
You should use a compressor when your audio isn’t consistent in volume. Likewise, you should use it when you want to change the aggressiveness or power of the sound. You can customize whether the sound is smooth or aggressive by dialing the compressor’s parameters.
A compressor has many uses. Here are some:
- It can control the peaks and transients of a signal, making it more consistent and balanced at levels. For example, a vocal track may have some parts that are too loud and some that are too quiet, making it hard to hear and mix. By applying compression, you can reduce the volume of the loud parts and increase the volume of the quiet parts, making the vocal track more even and clear.
- A compressor can shape the tone and character of a signal, adding punch, presence, warmth, or smoothness. For example, a drum track may sound too thin and weak, lacking in impact and energy. You can enhance the transients and harmonics of the drum track using a compressor, making it sound more punchy and powerful.
- It can enhance the details and clarity of a signal, making it more audible and intelligible. For example, even a well-recorded guitar track can sound dull because of the loss of nuances and articulations. A compressor can bring out the details and brightness of the guitar track, making it sound crisper and defined.
- A compressor can glue together multiple signals, creating a cohesive and harmonious sound. If your mix sounds disjointed and chaotic, applying compression can blend the instruments and create unity and balance in the mix.
- A compressor increases the loudness and perceived volume of your mix. You can reduce the dynamic range of a master track and increase its average level, making it sound louder and fuller. Likewise, a fast compressor on percussive instruments can prevent them from triggering the master limiter too easily.
Tips For Using A Compressor Effectively
Compression can be a powerful tool to improve the sound quality and character of your audio signals, but it can also be tricky to master. Here are some tips and best practices to help you use compression effectively:
Use Your Ears
The most important thing when using compression is to use your ears and listen to the results. Don’t rely too much on the meters, numbers, or presets. Every signal is different, and every situation is different.
Adjust the settings according to the specific signal and the desired effect. Compare the compressed and uncompressed signals and check if the compression improves or worsens the sound. Furthermore, if you can’t hear the difference, you may not need compression at all.
Reference
A good way to learn compression is to use a reference track with a sound and genre similar to your signal. Listen to how the reference track uses compression and try to emulate it on your signal. You can also use a spectrum analyzer or a loudness meter to compare the frequency and level balance of the reference track and your signal. This can help you achieve a more professional and competitive sound.
Makeup Gain
Compression reduces a signal’s dynamic range and peak level, making it sound quieter and weaker. To compensate for this, you can use a makeup gain to increase the output level of the compressor and match it to the input level or increase it to achieve a louder and more consistent sound. However, be careful not to overdo it and overload the signal or lose the natural dynamics.
Bypass
A good way to check if the compression sounds good is to use a bypass switch to turn the compressor on and off. Doing so can help you hear the difference between the compressed and uncompressed signals and evaluate the effect of the compression. You can also use a bypass switch to compare different types of compressors and settings and choose the best one for your signal.
Mix Knob
A mix knob is a parameter that allows you to blend the compressed and uncompressed signals. This can help you achieve a more natural and transparent sound, as well as create some interesting effects. For example, you can use a mix knob to apply:
Parallel Compression
Parallel compression is a technique that involves mixing a heavily compressed signal with the original signal to add punch, presence, and loudness without losing the natural dynamics and transients. This can be useful for drums, vocals, bass, and buses.
With a mix knob, you can easily adjust the balance between the compressed and uncompressed signals without having to create a separate track or bus for the compression. A common starting point is to set the mix knob at 50% and dial in some settings. You can then tweak the mix knob to find the sweet spot between the dry and wet signals.
New York Compression
New York compression is a variation of parallel compression that involves adding some EQ and saturation to the compressed signal to make it brighter and more colorful. This effect adds excitement and energy to the mix, especially for electronic and dance music.
Serial Compression
Serial compression is a technique that involves applying two or more compressors in series to achieve a smoother and more controlled sound without over-compressing the signal. This can be useful for vocals, guitars, pianos, and buses.
The mix knob lets you adjust the amount of compression applied by each compressor without having to create a separate track or bus for each compressor. A common starting point is to set the mix knob at 100% for the first compressor and lower it for the subsequent compressors. You can then tweak the mix knob to find the optimal amount of compression for each stage.
Knee Knob
The knee parameter can be used to fine-tune the compression effect and make it more natural or aggressive, depending on the situation and the desired result. Here are some general guidelines and examples of how to use the knee parameter in a compressor:
- For signals that have fast and sharp peaks, such as drums, guitars, and synths, a hard knee can be useful to control the transients and add some punch and presence to the sound. A hard knee can also be used to create some creative effects, such as distortion, pumping, and ducking.
- For signals that have smooth and gentle peaks, such as vocals, bass, and pianos, a soft knee helps preserve the dynamics and adds some warmth and smoothness to the sound.
Summary
In this article, we learned about compressors, which are plugins that reduce the loudness variations in an audio signal, making it more consistent and balanced. We also learned about the different types of compressors, such as FET, VCA, optical, variable-mu, and digital, and their characteristics. Finally, we learned some tips and best practices for using compression effectively.
Compression can be a powerful tool to improve the sound quality and character of your audio signals, but it can also be tricky to master. I hope this article helps you use a compressor with confidence and creativity.
If you’d like to learn more, check out this article about mixing. Be sure to check out the Learn page to see similar articles.
Insightful!
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