Mixing With Compression
Compression is one of the most powerful tools in your mixing toolbox. Applying it to your mixes is almost always a great way to improve them.
Compression isn’t the easiest effect to use, but having the right approach helps. If you understand the fundamentals and have a clear game plan, leveraging the power of compression is very achievable.
What is Compression?
Compression is a way to make the volume level of your tracks more consistent. It takes the louder parts of a track and makes them quieter, resulting in a more consistent level of volume.
Figure 1: A simple snare sample. By adding compression, the loud parts of the audio are turned down in volume and the quiet parts are left alone.
By applying compression, you reduce your track’s dynamic range. Dynamic range is the difference in level between the louder and quieter parts of your tracks.
Compression usually accomplishes one of two things. It either reduces the dynamics of your track, or it enhances the tone.
When To Use Compression
When you think about compression, think about dynamic range. The more dynamic range your track has, the more impact compression will potentially have.
If your track doesn’t have much dynamic range, compression won’t be as effective. There might be an opportunity for compression, but it will be more subtle.
Figure 2: A very dynamic sound (left) and a much less dynamic sound (right). If you applied compression to both, which sound would be effected the most?
Compression is usually more impactful for vocals and drums, which both have a lot of dynamic range. For instruments like guitar, bass, and synth, compression will usually be more subtle.
In any given situation, think about your tracks and what dynamic and tonal adjustments might be useful for them. If you aren’t sure what you can achieve with compression, don’t be afraid to experiment. You never know what great results you might come up with.
How to Use Compression
Most compressors have five fundamental settings: threshold, ratio, attack, release, and make up gain. If you focus on mastering these variables, you will get the most out of using compression.
Figure 3: Logic Pro’s Compressor with the most important settings boxed in red.
There isn’t a universal order of operations for applying compression, but I like to use the following order when I add compression to my tracks.
Step 1: Set the Threshold
Threshold determines what (or how much) sound will be compressed. The threshold is the level (measured in decibels) where everything louder than it will be compressed, leaving the quieter parts of the track in their original form.
If the threshold is set to -10 dB, then everything louder than -10 dB will be compressed. If the threshold is set to -20 dB, everything louder than -20 dB will be compressed.
Figure 4: Different threshold levels.
The lower the threshold, the more aggressive the compression will be, since more of the track will be effected by the compressor. As a good starting point, I like to set a threshold level that applies to just the peaks – maybe 25% of the overall track. This keeps the focus on only the louder parts, keeping the compression more natural.
Step 2: Choose a Ratio
Ratio determines how much volume reduction will be appliedto the portions of the track selected by the threshold. Ratios are formatted as 2:1, 3:1, 4:1, 10:1, etc. This is a relationship between the amount of volume reduction for every decibel of signal above the threshold.
If the ratio is 2:1, then the sound above the threshold will be divided by two (half of the original level). If the ratio is 4:1, then the compressed sound is divided by four (one fourth of the original level). A ratio of 1:1 indicates no compression.
Figure 5: Different ratios.
The higher the ratio, the more dramatic of an effect the compressor will have on your track. To keep the compression gentle but noticeable, I usually start with a ratio between 2:1 and 6:1 to start.
Step 3: Find the Right Attack
Attackdetermineshow quickly compression will be applied after the audio level exceeds the threshold. This is a question of delay. Do you want to lower the volume immediately, or wait a little bit? Attack is measured in milliseconds.
Figure 6: Different attack times.
Fast attack settings (under 10ms) will give your the most control over the sound and the dynamic range of your track. Slower attack settings (tens of milliseconds) will allow the initial sound to come through untouched before compressing the rest of the sound, creating a punchier effect.
Step 4: Dial in the Release
Release determines how quickly the audio will stop being compressed after it returns to a level beneath the threshold. This is similar to the attack, except it applies to the end of the compression process. It is also measured in milliseconds.
Figure 7: Different release times.
The shorter the release, the more immediate the compressor will stop working. In some situations, this will make the compression sound unnatural as the signal level snaps back into place.
A slower release will result in a smoother, more gradual transition. This might make your track sound better, but too long of a release will mean that some of the quieter parts of your track may get even quieter.
Step 5: Balance with Make Up Gain
Make up gain adds or reduces gain to the track signal after compression is complete to adjust its overall level. Compression often turns down the track volume since it is reducing the loudest parts of the track.
Make up gain is used to bring the level back up to a similar level as it was initially, meaning that only the compression effect is left and no changes to the overall volume are made within the plugin.
As you apply compression, play with different combinations of settings and listen to the results. If you are struggling to create a meaningful, beneficial change to the track, it’s okay to skip compression. It isn’t required on every track.
There are no “correct” compressor settings that can be applied universally. The numbers will be different for every situation, and even trying to establish certain ranges can be difficult. To find the right settings, you have to listen to the changes made by the compressor. Here are some tips to help you through this:
- Always remember what you are doing, both technically and artistically. What are you doing when you adjust the dials? What artistic effect are you looking to achieve?
- Use extreme settings to understand what you can do with compression on a particular track. Once you hear those extremes, you can dial them back to more nuanced levels.
- Watch the gain reduction meter in your compressor. Are you actually compressing, and when is it happening?
- Close your eyes and listen to the differences, particularly by bypassing the plugin and going back and forth. Hone in on the difference and and hear it with your ears. If you can’t hear anything, that’s okay. Not everything needs compression, and with more experience, subtle changes will become more noticeable.
- Listen at lower levels. It makes it easier to hear the subtle tonal changes on a track.
- Listen to your compressed tracks within the mix and in solo. Both perspectives will help you understand what you are doing and how the changes effect the overall song.
Practice Makes Perfect
Just like anything in music production, using compression is a skill. Compression is often more difficult to become proficient at than other things, but that doesn’t mean you should avoid it.
When you’re just starting out with compression, it’s important to be patient and practice with it as much as you can. Try it on different instruments, try it in situations that you think will and will not work, and focus on hearing the differences.
Over time, your ears will become accustomed to hearing what compression does, and it will quickly become a powerful tool in your arsenal.
Now it’s your turn. Take one of your songs, and look for ways to improve it with compression.
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