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Compressors vs. Limiters vs. Volume Automation: What’s the Difference?

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No matter how carefully you set up your microphones, position your instruments, orient the projection of your vocals, or select a virtual instrument or audio loop for your mix, there will always be volume level inconsistencies in your tracks. It’s a fact of life.

An occasional dynamic passage may suddenly cut through the whole mix, or an especially soft sound will get lost here and there, or some of your tracks will turn out smooth and consistent and others bouncy and frenetic. Either way, putting time and effort into smoothing out the dynamics within your volume levels is par for the course in any mixing project.

Obviously you will spend time setting relative volume levels between your various tracks until you achieve the right balance of sound for each component sound in your song. But, before you do this, you’ll save yourself a lot of grief and produce more solid sounding results if you spend a little time working on creating consistent volume dynamics in each track first.

Dynamics refer to the degree of the “up and down” in the volume level changes, as opposed to the overall average volume level of a track. You can easily modify the overall volume level of a track simply by adjusting its fader. Adjusting the dynamics, on the other hand, takes a bit more finesse.

The three primary ways you can control dynamics in a track are:

  • Volume Level Automation
  • Compression
  • Limiting

Let’s take a look at how all these methods work, and consider in which situations they would each be of greatest value to us.

Volume Level Automation

The easiest, most accessible method to control volume dynamics in a track is through the use of volume level automation. This is a very literal process in which you guide the volume fader louder and softer as needed in order to smooth out the apparent sound level produced by a track at any given time.

In most modern digital mixing platforms, this can be done by either recording your manual real-time motions of the volume level fader for a particular track, or by drawing in the instructions for the fader motion in a special volume level automation lane associated with the track of interest. They both produce the same net results, so you can use whichever suits you best.

Often you can view a recorded waveform and easily see where there are notably loud or quiet sections and add in appropriate volume level automation in those regions in order to even out the resulting sound output. However, not all sounds are created equal.  Certain sounds might come across quite clearly even if they appear to have small waveforms, while other sounds may have large waveforms and produce relatively quiet sounding results.

So, if you want to even out the dynamics with volume level automation, it’s usually in your best interest to listen through the entire song and make adjustments all the way through each and every track one at a time. If you put in the time and effort to do this, you may be able to make a very nice, clear, even presentation of sound for each track, which can then all be leveled balanced relative to each other for a beautifully blended natural sounding mix.

So what are the downsides?

Well this takes time. Unless you work with automating volume faders all day every day, you’re probably going to have to redo, revise, and refine all your automation for each track a number of times until you get it just right. If you have a large number of tracks in your mix, this whole process can become incredibly time consuming.

That brings us to our second method.

Compression

With the use of a compressor, you can quickly damp down excessive volume level peaks in any of your tracks. By setting the compressor threshold properly for each track, you can effectively control all dynamic bursts from that track that reach above a certain volume level. Then setting the compression ratio allows you to dial in exactly how strongly you want to dampen those spots with volume levels above the threshold you set.

With a little practice you can use these features of a compressor to mimic your volume automation efforts that bring down loud volume sections in each track, and do so in a much more efficient manner.

Compressors also offer other features to provide further adjustments to the sound of your tracks. In particular, you may want to also try adjusting the attack of the compressor, which when applied in conjunction with properly aligned threshold and ratio settings, can alter the sense of dynamic attack for the entire track. This means you could potentially add a little pizzazz to a track that feels a bit lackluster compared to other tracks, or soften a track that’s a bit too lively feeling relative to the other tracks in the mix.

In addition, you can adjust the makeup gain on your compressor to raise the overall volume level of a track. By boosting the makeup gain you can make quieter portions of the track stand out more clearly, and then readjust the threshold and ratio settings to further dampen down those portions of the track that may now start to sound too dynamic.

So, with the ability to mimic volume level automation, plus add additional sound characterizations to your tracks, why not just use a compressor every time and call it a day?

There are certainly many cases when using a compressor is a great solution, but there are almost always going to be outliers in any recorded track that don’t quite fit your “one size fits all” compression settings. Those outliers require you to still utilize good old fashioned volume level automation in order to manually place them close enough in line with the rest of the track to work well with your compression settings.

Also, there are often tell-tale sonic signs of the use of compressors that may be undesirable in certain tracks or certain genres of sound or music. Specifically, there’s often a sudden clamping down feeling or squashed sound to your music whenever a compressor kicks in strongly. And while clear and present sound may be nice in some instances, sometimes your listener would like to hear a little space in the sound, rather than everything pushed right up into their faces all the time.

Now with the pros and cons of both of these methods in mind, let’s consider the final means for controlling dynamics in your mix.

Limiting

In reality, a limiter is essentially another type of compressor. The difference is that you mainly only use a limiter for catching very tiny peaks or very brief peaks. Unlike regular compressors, which begin to smooth out any dynamic volume level peaks above a certain amplitude, a limiter will “limit” the amplitude to no more than the level you set.

Because it tries to chop off the volume level at a certain point, you need to be careful how much you apply it and basically save it to control only the last little bit of excess dynamics in a track. In other words, think of it as your final volume dynamics safety net.

There are certain sounds in which it’s possible to use a limiter more heavily; this would be anything that has extremely fast attack/decay, such as percussion hits from a single drum, or sound effects with quick bursts of sound in them. For these types of sounds you can generally use a limiter more heavily to greater effect than a compressor, since they come and go so quickly that there may not be time for a compressor to ease into the dynamic level control. Limiters tend to sound more natural, too, since they make fewer alterations to the original audio waveforms.

You’ve probably already come to the punch line regarding the use of volume automation vs compression vs limiting. That is, many tracks in your mixes will benefit from using all three in combination.

  • Use volume level automation to smooth out the most blaring quiet and loud sections in the track
  • Use compression to further smooth out the dynamic range in an even and consistent manner with the addition of presence control.
  • And use limiting as the final volume peak control for any remaining little peaks that may remain.

However, each track and each mix is going to be unique, and you will certainly want to apply whichever individual or combination of volume level dynamic range control provides the right feel for every unique situation. Good luck!

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Erik Veach
Erik Veach

Erik Veach is the owner and lead audio engineer at Crazy Daisy Productions, providing mixing, mastering, and sound editing services since 2001. He is the original pioneer of automated intelligent mastering systems, introducing them for use in professional music production in 2003.