Understanding Audio Compression and Using a Compressor (Easy Way)

 

Welcome to the world where digital things are now incorporated, at this stage, I don’t think you need any additional hardware tools to solve your entire problem when it comes to music production.

The problem new producer encounter is lack of understanding and I wouldn’t even say lack of understanding but would preferably say they follow the wrong path when learning music production, this is normal, I have been in such situation before.

I would have loved to explain all I know about music production, but I want to clear the air once and for all about using Compression rightly.

If you are looking for a short guide on Compression then this guide is not for you, if you have been looking for a complete and easy to understand guide about Compression, then you are at the right spot. Enjoy your stay!

Before I go into the Tofu and Potatoes of an audio compressor, I’ll like to introduce some core concepts which would help in understanding the topic better and also yield in an interesting intensive guide, let’s get cracking 🙂

What Is An Audio Compression?

Audio compression is an effect that is used to control the loudest and the quietest part of an audio signal, simply put, it is a processing tool that is used in controlling the overall dynamics of an audio portion.

Dynamics or Dynamic range in audio is the ratio of the quietest sound, and the loudest sound in an audio sample, the ratio in dynamic is the relationship or the difference between the softest sound and the loudest sound.

View dynamic range as the Lows and highs in an audio sample, and view compression as the “processing boss” altering the dynamic range of a given signal to achieve a consistent sound, you will see why this is important in the coming section.

When To Use Audio Compression

Usually, we can control the volume of a sound with just a volume fader (fader brings the amount of volume higher or lower), but a problem arises.

If the audio is reduced, the loudest part will only be heard while the quietest part dies out and if the volume fader is increased, the loudest part is just heard clearly while the quietest portion is heard a little bit, this makes it sound odd with your overall mix.

With compression, the softer sound would be louder, and the louder sound would be softer automatically, making the overall mix balance.

They are a variety of challenges when recording an audio material, and a perfect example is a noise coming from an adjacent room.

No matter how great an audio material may be, I want you to accept the fact that recordings can never replicate live music.

With compression, a sound can be much more listenable, while also maintaining the audio integrity but this doesn’t mean using compression would solve all audio issues, some sounds won’t just work with compression, basic eqing and levelling would resolve common audio issues most of the time.

Another useful thing to note is the transient of the sound, and this is one of the major factors you should consider before squashing the hell out of your track or music with a compressor.

Loosely speaking, a transient is a spike attack in your sound which occurs as a waveform builds rapidly from silence to a peak, an excellent example of a transient spike is a percussion hit or a drum hitting, etc., you will often find this in a similar snappy instrument or samples.

Transient example in snare sample image

Think of it this way, as a drum sample hit, there’s a rapid peak (the most extreme value or height) in a waveform that slowly dies out, the rapid peak is what is called Transient, the image below explains better.

Showing example of a transient in kick sample
Showing example of a transient in kick sample

Why Do You Need to Understand Transient?

Transient helps to determine if compression is useful or not, although it depends on what you are trying to achieve, for example, if a track has many transients as a drum hit, then the Pros might say its a good sign of audio with a good dynamics.

With a compressor you will be able to reduce the level of the louder signal and also amplifies the softer signal, making the whole audio portion sounds even, and also finding the perfect balance in the audio signal.

A Scenario of How a Compressor Works

Let’s assume we have a “dry broom” which is 10 inches long and a deep bucket containing filled water, suppose you are holding the broom without putting it within the bucket, then we can conclude that the broom is dry ( untouched! ).

Now, imagine putting 2 inches of the “dry broom” within the bucket, we can conclude that we have 2 inches of the broom wet and 8 inches of the broom dry (2-inches touched!), what goes in is exactly what comes out.

Things would become more evident when I explain in compression terms. Mainly we have two parameters which control how the signals are processed, the Threshold and the Ratio, and you will understand what those terms mean and how to use them in the next section

Understanding Threshold and Ratio

The Threshold determines when to start compressing while the Ratio controls the amount of compression that will be applied to the audio signal.

Sending an audio signal into a compressor for processing without specifying how the signal is to be processed would resolve in an uncompressed sound, which applies to the above scenario (untouched!).

For compression to take place, we need to tell the compression when to compress (Threshold) and the amount of compression that will be applied simultaneously (Ratio), they are still more compression parameters I will explain in the coming section.

Telling the compressor when to compress without specifying the amount of compression would yield in an uncompressed signal, what you input is what you get, for the compressor to trigger, we set the amount of threshold and also the amount of ratio.

Practical Use of Threshold and Ratio

For this guide, I have an imaginary Kick peaking at -2db, and as said above that mainly we have two knobs or parameters that control how the signal is processed, one is the Threshold (determines when to start compressing the kick), and the other is Ratio (controls the amount of compression that will be applied to the kick).

Suppose I am unsatisfied with the kick and I want to adjust the dynamics, I first set my threshold to -10db, it tells the compressor I want to work on signal above -10db, and pass through the rest untouched.

Setting the Threshold won’t do anything to the Kick as I haven’t specified how I want the volume to be reduced, and this is where “Mr Ratio” comes in.

Repeating this, Ratio Controls the amount of Compression (how you want the volume to be turned down or let’s say gain reduction) that will be applied to the audio signal (e.g., kick, bass, etc.) when the Threshold point is reached.

If I set the Ratio at 4:1, then I am merely telling the Compressor to turn every 4db above the Threshold to 1db (making the peak/gain to be reduced). Don’t get this? I will simplify that further, all I need is your attention.

The Kick peaks at -2db and I have a threshold of -10db, this just means I have a difference of 8db between the Threshold and the peak(-2db), think of it this way, the threshold tells the Compressor to start compressing when the signal reaches -10db.

How much should the compression be turned down? That is where Ratio comes in, and with a ratio of 4:1, it tells the compressor that every 4db above the threshold should turn to 1db, it would do something like this:

Hey “Kick”, I can see you are peaking at -2db, and I have a threshold of -10db, the difference between the threshold and the Kick peaking at -2db is 8db, so I will only act on 8db.

With my ratio of 4:1, I will only give you 2db out of your 8db (every 4db above the threshold should turn to 1db), subtracting two from -10db, will make our processed kick to peak at -8db, still puzzling with the math? Check out the image below for better understanding and the  formula I used in calculating the processed output!

Threshold and ratio uses in compression image
Threshold and ratio uses in compression

Threshold + ((Peak – (Threshold)) / Ratio)

for example:

Peak =-10db + ((-2db – (-10db)) / 4) = -10db + (+8db / 4) = -10db + 2 = -8db

Now that you understand what a Compression does, when to use, and the main two parameters, Threshold and Ratio, in the next section I will introduce and explain the other useful compression parameters you should use. Let’s get moving on 🙂

Understanding Attack and Release In Compression

Attack determines how quickly the compressor will react to signal or sound above the threshold. You remember I had a Threshold of -10db and a Ratio of 4:1, using an attack parameter will let you set the amount in time you want the compressor to act.

For example, Once the signal reaches threshold point (-10db), the attack will tell the compressor, “hey I want you to start compressing after (n)millisecond “, simple right!

Just as it is necessary for compression to determine when to react to sound, it is also necessary for compression to determine when to release the reaction once it goes below the threshold, this is called Release.

It is the time taken for a compressor to stop compressing after the level has fallen below the threshold.

An easy way to remember this is:

Attack kicks in when a signal goes above the threshold and release triggers when it goes below the threshold.

In the next section, I will explain the practical uses of Attack and Release.

Practical Use of Attack and Release

Building on my imaginary Kick, which peaks at -2db, a threshold of -10db and a ratio of 4:1, to bring out the attack of my kick or let me say to bring out more transient of my kick, I’ll set up a slow attack of about 14ms and a moderate or fast release of approximately 400ms.

Why this technique works on drums or percussive is because percussive sound consists of attack and a body. The attack is the loud initial part of the sound, while the body is the “meaty” or quieter part of the sound.

A slow attack leaves the attack of the sound intact, and reduces the body of the sample, making it sound tighter, nevertheless, your no one goal when compressing a percussive sound is to achieve a good balance between the attack and body of the sound, for better punchiness and a presence.

In the next section, I will introduce parameters you should consider when using compression, and this is the gain knob, let’s clear things up in the next part!

The Gain Knob in Compression

Since Compression is a processing tool that reduces the overall volume of input, you should expect a quieter output, to make things look nice and clean, compensate the lost amount by using the gain knob, it would allow you boost the signal right back up to “make up” for the compression.

Some compressor tools feature an auto-gain option for automatic compensation, test with different tools to see what best fit your work.

I can unequivocally say you understand compression and how to use it in your music production scene, let’s see when compression is not useful in the next section.

When Not To Use Audio Compressor

If you find yourself solving an issue with compression and didn’t turn out the way you want, ask yourself if you can solve or achieve the desired effect with an eq or with just manual volume adjustments.

Most of the time, manual volume adjustment would solve the problem right away, and I want you to know that some audio materials don’t fit for compression, probably because they’ve already been compressed.

Compressors are different, and react to sounds differently, experiment with varying settings of a compressor and see how they affect the sound independently, choose your favourite one and stick to that.

Disclaimer: The above formula won’t perfectly translate or work accordingly, and that is due to various factors in compressor plugins, I highly recommend using your hear to test things out, this guide is just for concept on how compression works, if you follow the guide properly, you would know how the concept works and also how to use it in various aspect of music production.

Good luck with compression and I hope this article will guide you through. Let me know if I am missing anything in the comment section below.

References

1. Carr, J. (2014, January 1). Understanding Bass Compression/Compressors – A Guide to Using Compression Live and When Recording. Retrieved December 10, 2018

2. Steve Savage. (2014). Mixing and Mastering in the Box: The Guide to Making Great Mixes and Final Masters on Your Computer [Kindle Edition]. Retrieved from Amazon.com

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