The main feature of compressors in music is that it reduces the dynamic range of the audio signal. Simply, with its assistance, we can boost a quieter signal or reduce a loud audio signal. This process helps maintain a constant volume of your instrument or vocal. For example, if we hit a snare drum strongly, and the next stroke happens to be a little weaker, with the help of a compressor, we can equalize these two hits in volume. The differences between a loud and weak signal will be reduced. The same rule applies to vocals. If you move away from the microphone, sing a bit quieter, or lower parts of the song, your volume will be equalized.
A compressor, whether you have an external unit, built-in effect in your mixer, or favorite VST plugin in your DAW (digital audio workstation), can be of great use to you in achieving a good relationship between the instruments in your mix. The use of compressors live, and in post-production can be very different. Simply because when performing live, many factors affect the final sound, the dynamics of the instrument or vocals, microphone placement, ambient noise, etc.
Improper use of the compressor, ie its parameters, can lead to catastrophic results. You can use the factory presets and tweak them a bit according to your needs, but don’t rely on them. Learn the meaning of parameters, it will be of incredible benefit to you.
Compression Parameters
Why do we force you to learn the parameters instead of using your favorite presets? Simply, even if you find the perfect compressor preset for your current instrument or vocal track, that preset may not match the next recording or if some of the players change their patch. For example, if you touch the gain knob in the next recording or even worse, the guitarist lowers his volume or bass player touches his tone knob, the compressor will not work the same.
Additionally, if there is a need to work on different external compressor units, different digital mixers, or VST plugins, you will need much more time to handle it. We all know that when you get used to one device, one user interface, especially when you use premade presets, it is very difficult and time-consuming to adapt to another. It is now clearer to you why it is of great value to learn each function of the compression parameters.
Threshold
This parameter function manages the level when the compressor starts operating on the audio signal. This parameter is specified in decibels (dB), and you should set it to affect the high signal peaks.
Ratio
This parameter determines the amount by which the compressor changes (read reduces) the signal. For example, if the ratio is set to 4: 1, it means that for every dB that the signal exceeds the threshold parameter, it will be divided 4 times in dB. Confusing? Actually not at all, let me give you an example. If the signal exceeds 8dB louder over the set threshold, its output from the compressor will be only 2dB louder. So that means (8 / 4 = 2), and we get only 2 dB louder audio signal (instead of starting 8 dB).
Attack
This control determinate when the compressor starts affecting the audio signal. It is specified in milliseconds (ms). If the loud peaks in signal start happening at the beginning of it, you should set the attack parameter act fast (lower ms number).
Release
This parameter commands how long the compressor proceeds to affect the signal after starting compressing it. As an attack, the release function is specified in milliseconds. Since high peaks in audio signals do not last very long (for example in the snare or kick drum) then, you should use a short release time when using compression.
Gain
The gain parameter provides you with the ability to adjust the signal level coming out of the compressor. On some external devices, mixer built-in effects, or VST effect plugins there is an input gain function as well. As the attack and release parameter is specified in decibels. Since adding compression generally reduces the overall loudness of compressed audio signal, use gain control to boost the level back to some point where be equally leveled as input gain.
Knee
Again, depending on the model, but most compressors are equipped with this parameter and will allow you to choose between soft or hard knee. Both refer to how the compressor acts as the input signal meets the threshold. For instruments like drums, when there is a need to quickly compress the high peaks, the hard knee is used. The soft knee should be used on vocals and other instruments where the audio signal does not have that fast and loud peaks.
How should I use compression on various instruments?
There is no one and only, and the right way for applying compression. Everything depends on input signal as well on an instrument, playing style of the performer and, in the end, genre. If you read various “recommended” compressor setups for certain instruments on the web, stop wasting your precious time. That is no different from using a premade preset. Most important of all is to learn how to listen and develop your hearing. It takes time, but it pays off at the end. There is no point in overcompressing any instrument, you will not achieve anything good, especially with live instruments, you have to let it breathe in the mix. The effect chain is very important in this case also.
Additional effects in that chain should, and some should not be placed before the compressor since compression may deform its sound. For instance, the equalizer will play its role the best if you put it before the compressor, while the delay, reverb, and such, will work best if placed after the audio is compressed. Since many audio engineers love it, find it a challenge, and there are a lot of approaches at the same time, let’s start with the drums.
Drums
The dynamics depend on the genre, as well as on the style of playing. So a different setup should be applied. In any case, whatever approach you take, one thing will constantly bother you – bleed. Normally, when you record drums, and while playing kick, snare, hi-hat, other microphones capture the same thing. That bleeding can cause your mix sound poor. Before any tweaks on the compressor, you should get rid of the bleed. You can get rid of it using the gate or manually cut out all unnecessary parts in the recording. Parallel compression is the go-to approach for getting the full sound of the mix. Mostly for kick and snare since these two components are the ones you hear all the time.
Bass
Depending on what tone of your bass guitar you want to achieve there are various approaches to how to achieve this. You will definitely need a compressor for the desired solid sound, in addition to at least EQ. After gain setup and EQ of your favorite bass frequencies, you can head to the compressor. In addition to cutting loud bass peaks (especially those in higher frequencies that can lead to a sloppy sound and not matching the timing with the kick drum) with the help of one trick, we can get that great bass sound. If you don’t want a tight slap bass, but a rich full one, adjust the attack parameter so that you literally can’t hear that “cling” tone from triggering the bass string. That can improve sloppy bass, as well as playing along with kick drum.
Guitar
The settings for electric and acoustic guitar can never be the same. While you can compress the electric (it is even desirable), with the acoustic one you should pay much more attention. In acoustic guitar recording, there is much more dynamic oscillation, and therefore if you miss only 1dB when tuning the threshold, or for a few ms too much while tuning attack and release parameters, you can achieve disastrous results. Squeezed lifeless guitar. Compressing a distorted electric guitar gives it a powerful sound, and it seems to me you can’t overdo it. You might want to check out my other post about how to eq and mix an acoustic guitar.
Piano
The piano can be the most complex instrument for mixing. Guess why? Dynamics! Again, depending on the genre. And above all, the piano is flowing in a wide frequency range. What happens when a piano player hits the chord!? Tons of frequencies and peaks which should be handled somehow. The overall sound if compressed much can be dominated by the loudest tone. Pianos have a great dynamic range that shouldn’t be killed with compression. Don’t ever ruin the piano’s dynamics with overcompressing.
Stings
The same thing as for piano and acoustic guitar, it’s an instrument with great dynamic range. On the one hand, for example for the violin, the chances of harder compression are higher because it works in a smaller frequency range, so it will be more difficult to overpower it with another tone.
Synth
Luckily, most of the synth’s patches already have compression applied, even pianos and strings, so they won’t give us headaches.
Check out my other post about the best monitor headphones for mixing
What is parallel compression?
The simplest explanation of parallel compression is that it is the combination of the dry signal mixed with a compressed one. It is the most commonly used for drums but other instruments as well as vocals do not lag behind. Setting up is pretty simple. Route desired channel you want to apply parallel compression to the next empty channel. Load your compressor on that channel, set parameters to your favorite sound, and start blending with the dry signal. Comparing with compressed signals only, this mixed, parallel method has way more life in it.
Using parallel compression on drums can help keep all the dynamics of the instrument as well as add depth, and power to them. You can additionally utilize multiple parallel compressors to complement different characteristics of the drums. One of the compressors be for a punch of the kick, snare, and toms, one can bring out more the room tones, and one can be used to add excitement for the hiss and favors of the cymbals. Using this method could amplify and enhance all of the poor conditions of the recording. Another common practice for drum parallel compression is just the Kick-Snare setup.
This is a setup that is mainly focused on the kick drum and snare drum. When you blend that compressed signal with a full drums mix, tweak that gain reduction knob to find the perfect balance between and you’ll get rich, defined kick, and snare. Try this method with vocals as well, you will see that you will achieve a very interesting result.
What is side-chain compression?
The most powerful method with which experienced mixing and mastering engineers manage to get a super loud mix is nothing more than side-chain compression. This method is quite popular in EDM (electronic dance music), while it cannot be bypassed in other genres such as rock, metal, pop, and others. Personally, I adore side-chain and tend to practice it all the time. It’s so easy to handle (once you get it) and it will do an amazing job. Kick against all the other instruments in electronic music … or rock, metal, pop anyway, but in EDM it’s the most noticeable.
You’re probably wondering how the kick succeeds to break out and pump through all those instruments (bass, synths, etc) and you feel like when it shows up, everything else goes under it in a mix. If you could isolate all the other instruments you will be able to hear them like laid back waving in a certain tempo and up and down in volume. The answer is so simple: side-chain compression. I will explain to you the simplest and most common example. Kick and bass. You have one kick channel assigned, while another channel is assigned for bass. Route kick channel to bass channel but keep in mind that there should be no output through that channel, only input. We just want the bass channel to get a kick signal.
The next step is easy, just load side-chain compression plugin into the bass effect channel and start tweaking its parameters. You will be able to manage that at the moment when the kick drum is played, there is no bass sound at all. While as soon as the kick signal reaches some lower point, there is bass coming in. So, you may wonder, what is the point of all of this process? Let’s get back to the beginning of this paragraph where I told you how mixing engineers get super loud mixes. How do you think the two audio signals (in this case kick and bass) that dominate the low frequencies will act if they are played at exactly the same time? You are right! You’ll get one big peak and clash of these two sounds.
If you apply compression, you can get rid of that peak, but still, you won’t get that loud kick and loud bass. Trust me, you won’t even notice that slight time offset like 60ms and you will have a punchy kick ass well as rich bass right after it and the whole audio image will still act as they are played at the same time (or not, depending on your taste, read parameters, you used). This method can be used on any instrument or even vocals! Yes, if you want to make more room for vocals you can sidechain all instrumental and when vocals come in, everything will go bellow them. Really useful stuff you must agree. Your mixes can benefit from the side chain, it all depends on your imagination and creativity.
How do you use live sound compression?
Using compression on a live sound can be very tricky but also very helpful for achieving full and rich sound. If you have a lot of instruments on stage, and therefore a lot of microphones, if you utilize the compressor on most of them, you will have to raise the volume fader or even gain knob. That can cause the mic feedback or additional stage noise. Without having a gate, you should pay extra attention while compressing the live mix. The most often compressed instruments during live performances are drums, bass, vocals. Guitars too, but only if played over the guitar amplifier. Since most of the guitarist who has their effect chain pedalboard already has a compression applied.
What about live vocals?
Yes, why not!? Although you may be able to meet some singers who don’t like it. They are usually excused for being “choked”. True, it may be strange in their ears at first, but you have to convince them that they will get used to it. The more, it can help them a lot when performing songs, the less they will be forced. In any case, it will sound better because there will not be too much difference in dynamics, as well as loud peaks that can be irritating to the audience. Singers are used to hearing themselves much more than other instruments on stage, and the only cure to relieve yourself of pressure while making the perfect mix is for them to use in-ear monitors. You might want to check out my other post on vocal reverb and delay and how to get the perfect mix
First, you should do when mixing live vocals is a proper gain setup. After that, focus on equing and when you get the desired tone you may need to step back and finetune gain…again. Now, after you did all of that, use a compressor to achieve the richer sound of vocals without unwanted peaks. You may feel that vocals get a bit quieter, so you must reach after volume fader. If you plan to touch gain knob be extra careful since you may insert additional noise and even mic feedback in your signal.
Sources:
https://en.wikipedia.org/wiki/Dynamic_range_compression
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