When To Use CompressionApril 04, 2012
Compression is one of the most commonly used processes in mixing yet remains to be one of the most misunderstood. This could be due to the large amount of misinformation about dynamic compression that is out there. So when do you use compression? That is a great question and should be the next question once you have learned how to use a compressor, but for most it is not. Well let's see if we can separate fact from fiction and get down to the when......when to use compression.
This article is written with the assumption that you already understand how an audio compressor works. If you are not sure or need a refresher then I have written an article explaining the very basics of a compressor. I would recommend that you start HERE first.
So I have seen everything from folks giving out specific compression settings that you should use to some people giving advice that includes compressing everything on ever track. So first lets talk about what compression is and what it is not.
Compression is not:
A magic wand that you put on everything to make it sound better.
Something you use because you have to use ALL of the effects you have on every mix.
A tool for when you don't know what else to do.
WHAT IS COMPRESSION?
So what is compression as it relates to audio? Well we have two different categories of compression (there are more than two types of compression, but they all fit into one of these two categories).
Audio Data Compression – This type of compression is often used for completed songs. It comes in two forms, either lossy or lossless. In both forms there is a reduction of information that allows for the file to be smaller in size. Audio data compression happens when you take a track in .wav format and reduce it to an .mp3 format for example. This newly created mp3 file would be a compressed file as it would be smaller in size than the original .wav file. This is not the method that is used for a sound within a typical mix.
Dynamic Range Compression- Now this type of compression is the type that you would be use for sounds found in a typical audio mix. Dynamic range compression (also called audio level compression) involves reducing the dynamic range of an audio waveform. This dynamic range is the difference between the loudest parts and the quietest parts of that audio.
Imagine that you are watching your favorite movie on television at 2 o'clock in the morning. Now imagine that there is a part of the movie where the dialog is very quiet. Maybe they have to whisper as part of the plot to the movie. Now imagine there is a commercial break and here comes the loud talking announcer telling you about this great product you must have for only three easy payments of $19.95! If your television was equipped with a compressor then the low sounding dialog as well as the annoying commercial would all be heard at the same volume level. This would be known as dynamic processing.
WHAT IS DYNAMIC PROCESSING?
Dynamic processors come in many different flavors, but in very simple terms a dynamic processor is basically a processor which regulates the audio dynamics that are going through it. This can involve limiting, compressing, using gates and the like but by definition any dynamic effect could be called compression. Think of it like a giant volume knob. But unlike a volume knob it works proactively based on the sound running through it. See with a standard volume knob you would set it to the volume level that you wanted to listen to a given sound at. If that sound became too loud or too quiet you would then have to manually adjust the volume up or down to your desired listening volume. With a compressor it would take that incoming sound, process it and output that sound based on the compressor's settings automatically.
WHEN IS COMPRESSION NEEDED?
First let me say that those that say “compress everything always” seem to missing the point of audio compression. Now I will not say that this method is wrong because a lot of today's modern music is in fact compressed. Maybe even too much so depending upon which side of the loudness war you are on. That being said I think it is important to treat every mix as it's own project and therefore you would want to make your compression choices based on the sounds within that mix not based on some “must use” number system.
So when is compression needed when it comes to your mix? Well I have found that there are 4 reasons to compress a sound within a mix.
Dynamic Range – You are trying to limit the dynamic range in a track. If something is too low or too high this is a good reason to limit your dynamic range.
Add Punch – Compression can be added to sound to give it more punch and power. This is a great way to get your kicks to break through your mix. However punchy drums can also be had through EQ, a gate, a transient designer or distortion and saturation.
Glue – Buss compression is often used to glue sounds together and make them sound like they are from the same cloth.
Special Effect – Using compression as a special effect tool is a great way to get a unique sound. It could be something as simple as a pumping effect or even using a compressor in a musical way.
It is important to decide what you would like to do with your compressor before you start compressing. But all and all the main reason is for control of a sound or sounds whatever that control may involve.
WHAT SHOULD YOU COMPRESS?
That is a tough question to answer because every song is different and therefore your compression needs are going to be different as well. I don't think that certain instruments need compression where other instruments will never need compression, but there are some sounds that receive compression more often then not. Those two would be drums and vocals.
Compressing Drums – The use of compression on drums is a very subjective process. Some drums will require a lot of compression and some drums may need very little compression. It really depends on the genre of the track you are working on and the type of mix you are shooting for. Compression can not only be used like a volume controller but it can also help to shape tone and this is where it really shines when it comes to drums. When you apply compression to a drum the body of that drum can be heard a lot more making it easier to shape the other parts of the drum around it.
Compressing Vocals – Compressing vocals is something that many producers and engineers alike do to recorded vocals even if they don't completely understand why they do. There are many, many reasons you may want to compress a vocal. Sometimes it is for dynamics and sometimes it is more for effect, but if you are shooting for something a little more natural then the reason is simple. The reason is to help control the character of what that singer is saying so that it is consistent throughout the range. For example lets say you have a singer in your studio and you ask them to sing “you-you-you-you-you-you-you” as you play the piano keys gradually going up. With a really good singer the phasing of the word “you” should be easily heard from the bottom to the top without a change in the character of that word. If you are like me you don't just work with really good singers so that is where compression can make this happen for those that can don't do it naturally.
Another reason would be for a singer that has a really large range or the song has a lot of dynamics within it, so compression, vocal riding or animation is needed to make sure that the vocal remains the focal point throughout the whole song and doesn't get lost along the way.
Compression is a very useful and needed tool not only in the studio but also in radio, television, dance clubs and many, many other areas in which we need to hear all of the sound completely. When used correctly it can be your best friend to have around to get you out of a tough situation in the studio. When used incorrectly it can make the listener run as far away from your song as they can possibly get. Take the time to learn about compression. Get a half of dozen compressors that you can really count on and learn them well. This will allow you to make better choices and you mixes will thank you. Oh, and so will your listeners!
Stay tuned for more weekly tips and tutorials every Wednesday.
Article written by Alex Butler
Alex is an audio engineer, studio producer and freelance writer based out of Seattle, WA.