# Know Lots About Compression:



## Chris

Big List: Here.

Ripped from: samplecraze.com

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Compression is one of the most important elements in modern audio work, but it is perhaps one of the least understood and abused. Compression is used at every stage of the audio process and can be used for many different reasons from the mundane to the extravagant. In the first part of the MPC-Tutor compression series, well be looking at the fundamental controls and theory behind compressors.

*What is a compressor?*

In very simple terms, a compressor is a device that can automatically control the level of an audio signal. Imagine an engineer using the volume fader to keep a singers performance at a constant level, making fine adjustments at the right time  well a compressor does this automatically and a lot more accurately! 

*Type of Compressor*

There are many types of compressor, each one uses different internal components to achieve the desired compression. This leads to each compressor imparting its own unique sound on the effected material. Tube and valve compressors are certainly top of the drool factor, with their ability to add 'warmth' to a signal - and also add a couple more zeros to the price! Most budget compressors use solid state components, Joe Meek tend to use Photo-optical components that again, impart their own sound. Many modern compressors use a combination of technologies (such as the Behringer Tube Composer), and of course there are the software compressors designed to emulate all the aforementioned. What type you use depends on the type of music you make, the way you like to work, and your budget. Always remember that basically, a £100 Joe Meek is doing the same job as a £3000 Uriel - controlling the signal level - but each one will approach the task slightly differently and 'colour' the sound in its own unique way.

*Compressor Controls*

Compressors come with a variety of controls, but these are the most important.

Threshold  This sets the threshold level, measured in dB (decibels). When a signal exceeds this level, compression will be applied.

Ratio  This is the amount that the signal is reduced by the compressor. A compression ratio of 5:1 means that if the signal exceeds the threshold level by 5dB, the output signal only exceeds the threshold by 1dB. As you can see, the higher the ratio, the nearer the output level will be to the threshold level. When this happens (at ratios of around 20:1), we refer to it as limiting.

Attack  This is how long it takes for the compressor to act after a signal has exceeded the threshold level.

Release  This is how long it takes for the compressor to stop acting after the input signal has fallen back below the threshold level.

Output  After reducing the overall level of a signal, the output gain can be increased to bring the whole signal back to its peak level.

Hard knee/soft knee - While attack decides how fast a compressor acts, the compressors hard/soft knee characteristics decide how gradually the full amount of compression is applied. Hard knee compression applies full compression as soon as the attack allows, as shown below.

Soft knee compression actually occurs as the signal reaches the threshold, and is much more gradual than hard knee, as shown below. Soft knee is a much smoother, less noticeable compression over hard knee.

*What can compression do for my music?*

Compression can be used for many purposes, including:

- help instruments 'sit' more comfortably in a mix 
- bring out certain instruments from the rest of the mix 
- even out differences in levels on an individual instrument or whole mix 
- make all the instruments in a mix 'gel' together 
- subtly change the sound of an instrument 
- dramatically change the sound of an instrument 
- impart its own unique character to a sound


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## Chris

*Hooking it up*

A compressor isn't strictly an effect, it is a signal processor. With an effect, we tend to mix the effected signal back with the direct signal via the Aux send and returns on a mixer. With a compressor we want to affect the whole sound and only output the effected version - the original, unprocessed signal must not be heard (but we'll see later that this 'law' is regularly broken to good effect).

The easiest way to hook up a compressor to a signal is to use the insert points on your mixer channel. You'll need a TRS jack-to-Y lead. That is a lead with a stereo jack at one end (Tip, Ring, Sleeve), and two mono jacks at the other end. The stereo jack goes into the insert point on your mixer channel, and the mono ends go into the compressor - one in the input and one in the output. The signal is then re-directed from your mixer, through the compressor and back to the mixer again. If you have a stereo signal, you'll need two leads and a stereo compressor - never use 2 mono compressors on a stereo signal as this can lead to stereo discrepancies.

Now that your compressor is hooked up, let's look at some applications.

*Limiting a signal*

There are many situations where you need to make sure your signal never exceeds a particular level. The most common would be when you are recording vocals or 'real' instruments like bass and guitar - it's not uncommon for the performer to get a bit carried away and start playing too loud, causing your recorder to start distorting (particularly with digital recorders). Remember in the first part that we said that a compressor set to a high ratio like 1 in 20 basically stops your signal exceeding your threshold? Well, that's the exact effect we'd like to see here.

Firstly, set your compressor threshold as high as possible, then set your ratio to 20:1 or infinity:1 if you have it. The compressor wont do anything at the moment, as it's threshold is set so high.

When our signal reaches the threshold, we want the compression to kick in quickly, and then return back to normal as fast as possible once the peak has passed. This means setting a fast attack, a fast release, and preferably using a hard knee setting if you have one. An attack time of 1ms should do that trick, with a release of around 0.1 ms.

All that's left is to set the threshold. This needs to be comfortably above the 'average' playing level, but below the 'danger' level. While someone plays at a comfortable level, start dropping the threshold until you begin to hear a dip in the volume. Then get them to start playing a bit harder, and set your threshold again, but this time back off a little bit more. This should be about right. Get the performer to give it some welly, and note that the level never exceeds the threshold you have set. The idea is to keep most of the player's dynamics, but control the nasty peaks when they hit things a little too hard for your equipment's liking.

*Compressing a vocal*

Vocalists tend to cover quite a large dynamic range, from very quiet part to very loud powerful elements. A compressor can help smooth out the level differences in the performance, making the vocal sit more comfortably in the mix and help it stand out just when it needs to.

We want the compressor to act reasonably fast, but we don't want it to return to normal too quickly as this may sound a bit unnatural. So set the attack quite fast, while the release should be a medium setting around 0.5 seconds. A soft knee compressor will sound the most natural. 

Ratio will vary for different singers. Start with a setting of 2:1. Get your vocalist to sing at a quiet level and start playing with the threshold, until your gain reduction meter shows a gain reduction of 1 or 2dB. finally, adjust your output gain to bring your levels up to normal.

The idea is to bring the up the quiet parts and drop the louder parts so that your vocal becomes tighter and more compact.

*Smoothing out a bass part*

Bass notes tend to have a large initial attack peak that drops rapidly to a more constant, lower level. To decrease this initial peak, we set a fast attack time so that the compressor kicks in immediately, taming the peak. Also set a fast release. A ratio to start with would be around 4:1. Set the threshold so that the compressor only acts on the peaks of the bass part. In most cases a hard knee setting works best, although Jazz bass can sometimes benefit from a soft knee compressor.

After this type of compression, you should find that your bass part feels tighter and less 'all over the place', so it should sit nicely in the mix and have good presence.

*Adding punch to a guitar/bass part*

If you have a recorded guitar or bass that lacks some 'oomf' and isn't cutting through the mix well, you usually need to increase the initial attack transient. Yes, a compressor can do this as well! The idea here is to allow the initial part of the bass note through uncompressed, then compress the rest of the note. The resulting note should then have an increased attack transient compared to the rest of waveform. 

It's important to set a slow attack time - experiment to see what works best. A reasonably slow release works well. Reducing the threshold should increase the punchiness. 

*Increasing guitar sustain*

Sustain refers to the length of time a note lasts after the initial pluck. The higher the ratio setting, the longer the sustain will be. Try a fast attack and a slow release, then play a note on your guitar. While it is playing, adjust the ratio until you are happy with the level of sustain.

*Compressing Snares*

In the same way that we reduced the initial transient on a guitar or bass note, we tend to want the same effect on drum hits. By reducing this initial peak, we bring out the true sound of a snare - the crack - which actually occurs slightly after this peak. A fast attack and release works well, with a starting ratio of around 3:1. 

Experiment with the attack time - by slowing it down very slightly can completely change the sound of a snare, bringing out more of the actual stick than the drum. As with all examples, increasing the threshold increases the squashed sound.

*Cymbals*

A fast attack, but a slow release is necessary here, in order to keep the natural sustain of a cymbal. Try a ratio of 2:1 to start with. On the other hand, a shorter release time with a high ratio and low threshold can lead to the classic 'pumping' effect, where you can hear the compressor actually working - in most situations this sounds bad, but with cymbals it can actually sound good in some songs.

*Using a compressor as an Aux effect*

Compression can even out the levels of a drum performance, but sometimes this can be a bad thing, leaving the drums sounding weak with no feel. By placing the compressor into the send-return loop, we can mix the compressed signal with the uncompressed signal, leaving some of the dynamics, while benefiting from the definition that compression gives us. Try short attack and release time, with a ratio of around 2:1 and a low threshold.


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## Chris

Code:


SOURCE       ATTACK     RELEASE    RATIO     KNEE       GAIN RED. 
Acc guitar   5 - 10ms   0.5s/Auto  5 -10:1   Soft/Hard  5 - 12dB 
Elec guitar  2 - 5ms    0.5s/Auto  8:1       Hard       5-15dB 
Kick/Snare   1 - 5ms    0.2s/Auto  5 - 10:1  Hard       5 - 15 dB 
Bass         2 - 10ms   0.5s/Auto  4 - 12:1  Hard       5 - 15dB 
Brass        1 - 5ms    0.3s/Auto  6 - 15:1  Hard       8 - 15dB 
Vocal        Fast       0.5s/Auto  2:1 -8:1  Soft       3 - 8dB


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## Vince

important fact I learned today....

When mixing drums, apparently compression should come before the EQ. I was having all kinds of problems getting my bass drums to punch through the mix, even though the meter was saying the bass was peaking quite a bit. I pulled the bass drum EQ, put the compressor before the EQ, and BAM!!! The bass drums were loud, boomy, and shook the room. So, I guess it's good to compress the raw sound, then EQ to taste from there.

Also, I don't agree entirely with the matrix in your last post there, Chris. If you were to hit the compressor at 1-5 ms on a kick, snare, or tom, you'll just about completely destroy the attack. I could post some clips A/B-ing if you'd like. The compressor is kind of like a wah, IMO; you have to find the sweet spot. For drum recording, I've found the sweet spot on the compressor to be around 20-30 ms for the attack, and about 100-250 ms for the release. On the drums I'm recording right now, I was using a 12:1 compression on the bass drum with an attack of 25 ms and a release of 100 ms, threshold at about -15 dB. Same for the snare and toms, only the compression ratio drops to 4:1 for those drums because I want a balance between drum sound and attack. The higher the ratio, the more attack & the less the natural drum sound. It's great for added 'click' on bass drums and added snap on snare and toms, but you have to find a happy medium for your own taste.


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## Tombinator

desertdweller said:


> important fact I learned today....
> 
> When mixing drums, apparently compression should come before the EQ. I was having all kinds of problems getting my bass drums to punch through the mix, even though the meter was saying the bass was peaking quite a bit. I pulled the bass drum EQ, put the compressor before the EQ, and BAM!!! The bass drums were loud, boomy, and shook the room. So, I guess it's good to compress the raw sound, then EQ to taste from there.
> 
> Also, I don't agree entirely with the matrix in your last post there, Chris. If you were to hit the compressor at 1-5 ms on a kick, snare, or tom, you'll just about completely destroy the attack. I could post some clips A/B-ing if you'd like. The compressor is kind of like a wah, IMO; you have to find the sweet spot. For drum recording, I've found the sweet spot on the compressor to be around 20-30 ms for the attack, and about 100-250 ms for the release. On the drums I'm recording right now, I was using a 12:1 compression on the bass drum with an attack of 25 ms and a release of 100 ms, threshold at about -15 dB. Same for the snare and toms, only the compression ratio drops to 4:1 for those drums because I want a balance between drum sound and attack. The higher the ratio, the more attack & the less the natural drum sound. It's great for added 'click' on bass drums and added snap on snare and toms, but you have to find a happy medium for your own taste.




On a majority of professional boards; the dynamics section, which includes compression, normally comes before the EQ section in the overall signal chain. For the most part, it would defeat the purpose of adding EQ, and then squash the signal thereafter.

Settings can vary, depending on mics used, SPL's, polar pickup pattern, rolloffs, preamps, pads, etc. I usually stick to the 3:1 ratio rule for safety measures. Many recordings these days lack real dynamics and depth. It's more like a competition for who's the loudest, so many mixing and mastering engineers are asked by the artists, record labels, radio, marketing, etc. to compress the shit of their tracks, bringing up the noise floor: adding unneeded noise and mud. The general public who are oblivious to such, have conditioned their listening experiences to this.


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## irg7620

i'm highly interested in taking mixed material, and mastering it. i know that compression and EQ are used to get it to sound good before it goes to master. can someone point me in the direction to a source that tells me what to do to the audio i have created before i send it off to get it mastered?


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## Vince

irg7620 said:


> i'm highly interested in taking mixed material, and mastering it. i know that compression and EQ are used to get it to sound good before it goes to master. can someone point me in the direction to a source that tells me what to do to the audio i have created before i send it off to get it mastered?



Do NOT compress it. Let the mastering house do that.

All you need to do is properly mix the tracks down to a stereo track. If you want to make an uber compressed version for yourself as a rough master, cool, but that's NOT what a mastering engineer will want. They want UNSQUASHED material because it gives them 100x more room to work with.


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## irg7620

ok, i will do that. i completely forgot about posting in this thread. i should have remembered where all my posts are. thanks for the advice.


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## Jon

cool, must not over compress or you loose the little differences in volume
between the tracks that make the recording more natural and easy on the ear.


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## 7 Strings of Hate

good thread chris 
i can't really tell a big differance with most of these settings, i dont think my ear is listening for the right things


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## drawnQ

REMEMER:

when initially starting to add effects to a signal:
when you use a compressor it will inherently cut some of the lows and highs from the signal. it just happens that way.

its usually good to compress then EQ from there because you will lose some of the EQ'ing effects if EQ is used first. it will make it sound dull again and thus the EQ'ing you just did went to waste.


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## metalheadpunk

Found this on knol, Google's version of wikipedia..sorta

Audio Compression Explained - a knol by Lonnie West 

click the link for pictures

Unless you are a recording musician, you probably are unaware of how much compression used in everyday audio. This is the single most important tool in any engineer's bag of tricks, and it separates the pros from the wannabes.

Unlike other effects (EQ, distortion, reverb, delay, flange, chorus, etc), the compressor does not add coloration or extra material to the audio signal. It simply changes the dynamic properties of the sound. The ironic thing is that if it is used correctly, most people do not know it's even there. However, when used incorrectly (or not used at all) your work screams "amateur." Believe it or not, EVERYONE notices when it is absent or mis-used, even though they would not be able tell you what was missing.

A compressor flattens the dynamic range of a sound. Think of it as an automatic volume control, and you are not far off: it is as if you have an "invisible assistant" with his hand on the volume knob, and his only job is to keep the sound coming loud enough for you to hear well all times. How many times have you watched a movie where there is yelling, screaming, and gunfire, then they cut to a scene where some injured schlup whispers his last words, and you could hear it as well as if he were whispering in your ear?

Compression!

Not convinced? Try this experiment: Have a friend standing about 6 feet away from you scream as loud as possible, fire a gun, and then whisper. I can guarantee you won't hear the whisper.

Compressors use a ratio system to determine how much they flatten the dynamic range. A compression ratio of 1:1 means that for every one decibel of input, you get one decibel of output. Here is a chart showing with some reference volumes:


Figure 1

It is interesting to note that the decibel scale is logarithmic: each 3dB increase is equivalent to doubling the volume. If you compare 60dB (Speech at a foot away) and 120dB (Front row at a rock concert), the first response is typically "There's no WAY a rock concert is only twice as loud as someone talking!" It isn't. It's 20 times as loud.

Looking at the chart above, the Input sound is the vertical axis on the Left side, and the Output (what you hear) is the bottom. At a 1:1 ratio, a 40dB input sounds like 40dB, and 120dB sounds like 120db. Make sense so far?

Now let's look at what happens when we compress it.


Figure 2

This is our same chart, but this time we are putting a 2:1 compressor between the Input source and ourselves. Remember, a 2:1 ratio means that for every 2 decibels in, we get 1 decibel out.

At a 2:1 ratio, a 120dB noise (our front row rock concert) becomes a 60dB noise (conversation at a foot away). Again, there is the logarithmic nature of audio coming to fool us again. We think 2:1 means that it is reducing the volume by a half, but there is really much more going on than that.

Looking at the chart we can see that the dynamic range is reduced through the entire range of sound: everything from a barely audible 0dB to the choking sensation of your chest collapsing at 150db has been reduced to a manageable 0db to 75db.

At a 2:1 ratio: a 40dB input is 20dB, and 120db is now a quiet 60dB.

This is only half of the story, because what we really want to do is make the quiet sounds louder. Right now, we've succeeded only in making the loud sounds much more quiet. This isn't really that useful, so the output of a compressor always has a Gain control that brings the output back up to a "normal" level.

Here is our 2:1 compressor with the gain turned up so the loudest sound (our chest crushing 150db noise) is still 150db on the output:


Figure 3

If you compare the compressed to uncompressed sound, this is the result:
- The loudest uncompressed sound is exactly that same volume after compression,
- The softest uncompressed sound is quite loud after compression

By bringing the Gain up after compression, we have indeed succeeded in making the soft sounds louder. A quiet conversation at 40db is now somewhere between noisy traffic and a New York subway terminal. Nice!

Of course, there is no such thing as a free ride, perpetual motion, free beer, or perfect audio. While we did get our signal into a more manageable range, we also introduced a lot of noise into our formerly pristine recording. Every tiny background noise in the input source has been boosted so that things that were just at the threshold of hearing are now at a volume level louder than conversational speech.

This means that previously "invisible" sounds (say someone coughing in the distance, people breathing, walking, setting a can of soda on a table) are all crystal clear. (This is why they call out "Quiet on the set!" before they roll film!) For music production, the same problem manifests itself in different ways.

Commercial songs are recorded in expensive studios for a reason. Yes, they have top notch gear, but they are also incredibly quiet. Not only are environmental noises reduced past the threshold of hearing, but internal systems like air conditioning and plumbing are also designed to be quiet as possible. This is absolutely necessary because modern popular music is highly compressed. Most individual instrument tracks are processed, and the resulting mix often ends up being run through at least one stage of compression during mastering.

If you isolate a single drum microphone and listen to the track after raw compression is applied, you will hear amazing things. Squeaky foot pedals, noise from the cymbal stands, grunting (you think I'm kidding??), and worst of all: other drums that suddenly sound almost as loud as the one you wanted to isolate.

Take that same track recorded in the typical home environment, and it gets even more interesting. Between beats of this incredibly loud floor tom, you will hear the air conditioner kick in, the TV in the other room, whirring of computer fans, and worst of all: traffic outside.

Suddenly you are faced with the prospect of having given yourself a lot more work trying to ~remove~ these elements from your track, and that's just one track. The typical song will take 16 or more tracks, and the noise on all of them will add up. Is it worth it? Just for kicks you turn off the compressor and listen again: the background noises are once again insignificant, but all those undertones that make the instrument ~jump~ out bigger than life are gone too.

The solution is setting a Threshold level before the compression kicks in. But before we get into that, we need to take a closer look at how the decibel level meters on a recording console differ from the absolute decibel level used in the physical world. 

DECIBELS AND DECIBELS

So far we have been referencing dB as a physical measurement of how loud a sound is. In this realm 0dB is the point where you can just start to hear a sound, and goes up from there. In the recording studio, this scale is inverted.

In audio gear, all meters and equipment are set so that 0dB references the MAXIMUM loudness of a signal, and goes down from there. To get the best signal-to-noise ratio when recording, it is necessary to record a track as loud as possible without overloading the recording medium. Back in the old analog days, this was a no-brainer: if you recorded a track softly and then tried to play it back at a high volume, you'd have a ton of tape hiss.

To make it easy to determine how loud to record a track, the equipment is calibrated so that a constant signal of 0dB represents the loudest signal that the equipment can handle. When recording, the goal is to get the signal level as close to 0dB without going over.

Current CD's play back 16 bit audio. Without going into a lot of math to explain it, this translates to a maximum signal-to-noise ratio of 96dB. (When CD's were introduced to the public in the early 80's, this was a huge improvement over the 60dB that a phonographs were capable of!) Therefore, most audio gear currently in studios have meters that run from -92dB to +3dB. (The +3db is there for those brief peaks over 0dB, so the equipment doesn't distort.)

THRESHOLD AND KNEE

OK, so let's throw up a graph of our good ole 2:1 compression with Gain from Figure 3, but I am going to re-label the scale so that it matches what you will see in the studio:


Figure 4

In this example, we have the Threshold set at the minimum, which means the entire signal is processed. At a 2:1 ratio, for every decibel 2 decibels OVER the Threshold, we increase the output 1 decibel.

Let's assume we are trying to set the compression on a Kick Drum on a standard drum kit. Even at a modest 2:1 ratio, you will notice immediately that undesirable background noises have also been increased greatly. Particularly, bleedover from other drums is very evident after compression.

A lot of this will be solved by setting the Threshold high enough that the compressor doesn't start to work until the signal rises above that level. We've either watched the meters (or opened the track in an audio editor) and have determined that none of the background noise in this track ever rises above -30dB. Setting the Threshold at -30dB yields a chart as show here:


Figure 5

This is a little better. Background noises have dropped back to decent levels, and if we have a good quality recording in either a studio or very quiet home studio, we might be able to stop there. Note that the background noises are still louder than what they would be without compression. (For instance, the -40dB Bleedover is about -25dB or so). This is due to the Gain that we have added to the output of the compressor to bring the 0dB Input signal back up to 0dB on the output.

If the background noise is still a problem, you have a few options:
- Reduce the compression ratio,
- Re-record the track using microphone and isolation techniques to minimize the noises,
- Use a Noise Gate or Expander to reduce signals below the Threshold level to much lower levels.

Looking at Figure 5, you'll notice that the threshold level where the two lines intersect is a "hard" intersection. This means as soon as audio crosses that line it goes from one amplification factor to a totally different one. On subtle compression ratios, say 3:1 and lower, this isn't very noticeable. On higher ratios, and/or certain types of program material, it creates a very harsh sound. This is where the Knee control comes in.

The Knee basically sets a gentle curve between the two amplification lines. Depending on the compressor, your options will vary. Some only have an option of a "Hard Knee / Soft Knee" which means either: A) the Knee is off and you have a hard intersection like in Fig. 5 (Hard Knee) or, B) the Knee is on and there is a curve to ease the transition from one amplification line to the other.

Some units will allow you to specify the amount of knee yourself: the greater the Knee, the wider the curve. The Knee is a very subtle control, and adjustment of this parameter is totally a matter of taste, and what sounds best with the compression and material you are working with.

ATTACK AND RELEASE

The compression ratio and threshold allow you to control the overall volume of the signal. Other than the ability to bring up sounds that are in the background, they really do not change the character of the sound you are working on.

The Attack and Release controls, however, will have a huge impact on the sound. Both the Attack and Release controls are time-based, which means their settings are measured in milliseconds.

This is the short definition of what the controls do:

Attack: The number of milliseconds before the compressor reacts to a signal once it exceeds the Threshold.

Release: The number of milliseconds it takes to return the compressor unity gain (1:1) after the signal falls below the Threshold.

Using our "invisible assistant" analogy from earlier, the Attack time is how long it takes him to react to a change in volume before he starts turning the volume knob: The longer the Attack time, the slower his reaction.

Let's say we are watching our action movie again, and our trusty assistance is sitting there with his hand on the volume knob. We are watching a quiet, tense scene where there is a bomb counting down the last few seconds, and a sweaty guy is sitting there with a pair of wire cutters. Our assistant has the volume cranked to 11 on a scale of 1 to 10, because we've ~got~ to hear the little tick of the clock, hear the guy's nervous breathing, and hear the drop of sweat as it falls from the guy's forehead onto the table.

Oops, surprise! The drop of sweat shorted out something and the bomb exploded 3 seconds before we thought it would. If our trusty assistant has a slow reaction time, our Dolby Digital Certified High-Definition Theatre Surround Sound system with 50,000 watts of body crushing power will likely blow out every speaker, window, and eardrum within a 200ft radius because the volume was still cranked to 11 when the explosion happened.

In this case, we want our assistant to be supernaturally quick, and snap that volume back down to a reasonable level a split second after the beginning of the explosion occurs. That way we get to hear the ticking, hear the breathing, hear the sweat droplet, and experience that fraction of a second of oh-my-God-what-happened intense volume surge that makes us jump when the explosion first starts. Then, we'll get to hear the rest of the explosion and falling debris at a comfortable volume that won't break or damage anything, and won't cause the neighbors to call the police.

This scenario plays out just the same when compressing an audio track. Here is the plot of a single snare drum strike:


Figure 6

Each of the vertical grid lines represents 10mS of time, and this entire sample is only about 210mS long: just shy of a quarter of a second. You can see that the first 15mS or so is the most intense, when the stick strikes the drum head. The rest of it is the decay from that initial hit.

For this example, we really want to bring out the tone of the snare, so we put a 8:1 ratio on it so that spring rattle during the decay comes up nicely. You set up the Threshold to about -30dB so the compressor isn't working on all the other noises coming through. Also, since we are using such a high compression ratio, we will need to boost the output gain to bring the levels up to where we want them. In this case, I put the gain at +16db.

Now it's time to adjust the attack.

If you haven't done it before, it's really instructional to sweep the Attack while the track is playing to listen to how it changes the character. At the minimum Attack setting (mine are digital, so they can go down to 0mS), you lose all of the punch of the initial stick hit. As soon as the signal starts to get loud, the compressor kicks in and squashes it back down. In this case the entire snare sound changes to a very even snare buzz / rattle, which is great for techno or dance music.

But, I like rock, so I need to hear some stick when the drummer hits a drum.

Moving out to about 15mS or so, it sounds nice. We have a solid of the initial hit, because it lets that first 15mS through untouched. Then the compressor starts doing its work, and brings up the rattle and buzz of the snare. At 50mS and higher, the compressor isn't doing much for us anymore because we've let most of the signal through untouched.

Here is the same snare hit, after we've worked with the compression to bring out the rattle:


Figure 7

You will notice that the first portion of the graph (the initial impact) looks identical to what was shown in Figure 6. The difference starts to be noticeable at 60ms (on the graph it's shown at 0.06 seconds) forward to the end of the wave. We now have a LOT more spring rattle than before, which is what we wanted.

Setting the Release time is a different affair. Many engineers rely on the tempo to determine the release time. The thinking behind this is that you want the compressor to just come back to unity (1:1) when it is triggered again, so that it "breathes" with the music.

To do this, play the track and just watch your meters as you slowly increase the Release time. You will hit a point where the compressor is still active when it is triggered again, back it off to the point just before that happens. Done correctly, the compressor will breathe with the music, and add its own character to the sound.

From here, it's time to sit down at the board and start playing! Once you master the compressor, your mixing will start sounding much better!


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## _detox

So I'm trying to figure out if what I hear in some of these songs is compression.

Like for instance in Bulb's Heliovice and Icarus Lives and Inertia with Casey singing, the vocals sound SOO clear and nothing really gets too loud. That IS compression is it not?


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## Fionn

probably a bit, but clarity has more to do with EQing, actually there is quite abit of comp present on the snare, the vocals sound pretty clean if there is compression its good, oh yeah you can notice that the vocal has more power in the choruses but the "volume" remains the same, this may have been done via automation but yeah probably it has compression on. 

The idea of compression (normally) on vocals is to even out any preformance issues concering dynamics. However compression can be used agressivly to emphasize transients not control them... This is the trick to get real punchy kicks and snares.


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## SomeChump

<3 Compression


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## TheGuerilla

Thank you, all of you nearly made me understood compression ! Very interesting topic !


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## JakeRI

thanks, this was so useful. i spent the last month not bothering researching how to fix a particular mixing issue I was having because I thought it would be a bitch to figure out, but this took care of it! (yes, I am a noob)


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## BURY142

Awesome thread, we just covered this in class the other day and this really helped me get a fuller grasp on the concept.


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## eggoboi18

This will help me alot in my mixes, thankyou!


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## MorbidTravis

isnt compression used to limit dynamic range and not audio level? because if you want to control your audio level, just put a limiter on or hand ride.

what i learned in school about compress is, if you took 10db of gain reduction you should add 10db from the output gain, so your levels are the same just dynamic range is limited to what you set it as


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## Fionn

dynamic range and level are so closely related there isnt much point making the differentiation, a level has no meaning if it has nothing to relate to and by having something to relate means there is a dynamic range between the two...

im confusing myself... 

you are right, but sometimes using a comp is an easy way to avoid level automation


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## waynesworld91

This site is killer info!


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## Enselmis

Does anybody have any recommendations for a great software compressor? Free of not, I'm just looking for a nice one to use instead of the standard ReaComp in Reaper.


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## KoenDercksen

I have heard good things about Bombardier.


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## Kurkkuviipale

Bombardier is kind of a mastering compressor plugin... it works well othervice as well, but might be a little costy for an all-around compressor.

Instead, why don't you check their (Stillwell) other compressor "Rocket". It differs a bit from an everyday compressor, but it's a really handy tool when you learn it.


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## manana

Why is it a bad idea to eq before comp? Wouldnt you want to get rid of the unwanted frequencies first?


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## Pendant

I like using maximus, but i'll check out bombardier


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## Zamoht

I like using the Golden Compressor by Kjaerhus Audio*
*


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## TheBotquax

This is a great video I found on compression! It doesn't really add anything new, but it let's you see just how compression affects the sound. Also, the method used in the video of maxing out all the settings at first, then concentrating on ratio, attack, and release separately really helped me find the sound I was looking for. I hope this helps some people 


http://www.youtube.com/watch?v=jhlMQV4PpOQ&feature=related


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## richardgstudios

Awesome thread, thank you all for sharing!!


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## sanus silentium

Existem


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## The Grief Hole

Thanks for the interesting post. I'm still slightly in the dark on one point though. I understand how we can use the compressor as a means of maintaining a consitent level but I was wondering if any one has any tips on using compressors a a means of achieving clarity between instruments in a mix (or this mainly down to eq-ing)?


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## Winspear

The Grief Hole said:


> Thanks for the interesting post. I'm still slightly in the dark on one point though. I understand how we can use the compressor as a means of maintaining a consitent level but I was wondering if any one has any tips on using compressors a a means of achieving clarity between instruments in a mix (or this mainly down to eq-ing)?



Well it kind of helps with that by nature. By bringing down the peaks for example the snappy transient of a bass, you are also allowing the other instruments to cut through more at that point in time.


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## The Grief Hole

EtherealEntity said:


> Well it kind of helps with that by nature. By bringing down the peaks for example the snappy transient of a bass, you are also allowing the other instruments to cut through more at that point in time.



Yes. Thank you. I have been using it more and more in my recordings and can see what you mean. I think the way I was approaching it was with the compressor on 'whatever' settings and then trying to dial in something from there. Now, I'm starting from a set point - no attack. full release. inf knee plus low input. Dial everything from that setting and I can start to hear the differences it is making.


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## bigswifty

manana said:


> Why is it a bad idea to eq before comp? Wouldnt you want to get rid of the unwanted frequencies first?



how I understand it is;

if you EQ before compression, the compression works within the frequencies that still remain. Whereas if you compress before EQ, then you will compress all frequencies, and then fix it to liking using EQ. Basically if you want to change your sound with EQ, then compress first. If your track is in greater need of compression, then EQ first.

hope I was in the ballpark and that it helps 

you guys/this thread are great thanks for the input


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## BaptizedBurning

Here's another great article about compression I found helpful:

Jezar´s compressor



[FONT=Arial, Helvetica] *How To Use a Compressor*

*Introduction*

Most effects processors are fairly simple to use; plug in an equaliser (for example), twiddle the controls, and listen to the output, and you pretty much know what you're doing, and all you need is some experience behind you. 
Compressors don't fall into this category. Plug them in and listen. What's it doing? Unless someone has told you, then you probably won't know. Play with the controls. What do they do? Don't know either. What do the indicators mean? Difficult to tell. It's all a bit frustrating really... 
Unfortunately you need to be *told* what a compressor does. Furthermore - even after you know what it does - someone needs to explain why the things that it does are considered useful. You won't figure it out for yourself. 
Normally - for non-technical people - the explanations of what a compressor does, are so bewildering that they end up even more confused than they were before: "xDBs in, equals yDBs out, over zDb threshold, according to this graph" etc. etc. 
Fortunately, I have a friend who explains it very well, and very succinctly: 
"What does a compressor do, Alan?"
"It makes the loud bits quieter."
"I see... But surely if it just makes the loud bits quieter, can't you then turn EVERYTHING right up, and make get everything really, REALLY loud?" 
"Exactly." 
So there you go. Simple isn't it? A compressor just makes the loud bits quieter, allowing you to crank everything up to maximum volume. But under what situations would this be useful? 
Firstly, there's the obvious application of making your CDs sound as loud as possible. This trend is starting to get a bit silly, and is beginning to prevent people from producing albums of good dynamic range. Nevertheless, if you master a rock or pop album with no compression at all, then the chances are it will sound pitifully quiet compared to the rest of the CDs in peoples record collections. It will probably sound like it has been severely under-recorded. Compression lets you get a much higher average level onto the CD without affecting the music too much. 
A very practical application of compression is in live PA setups such as a rock concert. There is a danger that very, very loud sounds will blow up the loudspeakers as well as risking serious hearing damage for those near the stage. The solution is to put a compressor in place. This makes the loud bits - and in this case only the very loudest of the loud bits - quieter, so as to avoid damage to equipment (and people). Such hard compression of only the very top peaks of music, is called "limiting", and is so useful that many compressors have a "limiting" function in addition to normal compresson, and so you will have to read the manual if you want to use this feature in addition to using the compressor for additional "normal" compression. 
Another example is that many vocalists have poor microphone technique. When they sing quietly, they sing *far* too quietly. When they sing loudly, they are *way* too loud. A compressor can reduce the "dynamic range" of the vocalist to a more managable level, which is why a compressor is sometimes called a "Dynamics Processor". 
Bass guitar is another instrument which can be hard to play consistently throughout a song. Any minor errors in the bass guitarists playing can leave "holes" in the song where the bass seems to disappear. A compressor can help keep the performance at a consistent level. 
There are obviously many other instruments and sounds that could benefit from compression at some time. 
So, as you can see, there are many applications for a compressor. Basically, in any situation where sound volume levels are getting out of control, a compressor can be used to "tame" the extremes of volume and keep it within a reasonable range, entirely according to your needs. Obviously a very powerful tool. 
Using one, on the other hand, is not so simple... 
Why? Because a high-quality compressor, with "good" settings, is designed so that you can't "hear" it working as such - so it's difficult to tell when it is doing the right thing. There have been red-faced moments for many engineers - including myself - when they have spent many minutes carefully adjusting the settings, proudly declaring them "perfect", and then realise that the compressor is in fact, switched off. Very embarrasing. 
There is also the added problem that the markings on the controls of many compressors are not very accurate. They are only there for a "guide" - and to help you restore settings later, so simply looking at the controls may not be a good indication of what the compressor is actually up to. 
Many compressors - including software plugins - don't even have meters on them, and needless to say, this makes it incredibly difficult to know if they are operating correctly. 
*Getting Started*

Because compressors have many different applications, the way that you use a compressor depends very much on what you are trying to achieve with it. In this article, we will look at four main applications of a compressor which are all quite different. Most applications are just variations on these four different uses, so they should serve as a good starting point for most of the things you will want to do. 
The four main applications that we will look at, are: 


Hard limiting - to prevent speakers or digital recordings from overload
Compressing an instrument or vocal
Adding "punch" to bass drums and bass guitars
Compressing a final mix
In addition, we will look at a specialised fifth example: 

De-essing a sibilant vocal
But before we get into these, let's look at the theory behind compressors and what the controls actually do. This is a little difficult to understand at first, so don't worry if you haven't "got it" the first time around. It will make more sense after you've experimented a bit with a real compressor in front of you. Note that not all compressors have all of these controls, and some compressors are very "minimalist" indeed. If you don't have all these controls, then look at the compressors instruction manual to see what preset values the "missing" controls are set to. *What The Controls Do*

Firstly, in order to compress the volume range of something into a more "workable" volume range, you need to have in your mind an idea of what the lowest "normal" volume level is, and what the "loudest" volume level is, and have a mental idea of how "loud" you are prepared to let the loudest get. 
The "Threshold" control, sets the volume level at which the compressor starts to do its work. Below this volume level, the compressor will literally do absolutely nothing. So you basically set the "Threshold" control to the lowest volume level at which you want the compressor to start working. We will discuss in the examples how you actually make this setting. Naturally, if the "Threshold" control is set to maximum, the compressor won't ever do anything at all because the level of the music is usually way below this level, and therefore remains totally unnaffected. 
The "Ratio" control sets how "powerful" the compressor is. At its lowest setting (1:1), the compressor literally does nothing, and is effectively "switched off". On the other hand, at its highest setting (normally marked 20:1 or even infinity-to-one), the compressor is 100% powerful - so powerful in fact that it TOTALLY PREVENTS the volume level getting even the *slightest* bit louder than the threshold level! Hard to believe? Try it and see. Set the compressor ratio at maximum, play some sound through the compressor and start turning the threshold level down until you hear the effect. If you are playing solo drums through the compressor the effect is quite astounding. 
The only problem with doing this is that (naturally) the total volume gets so much quieter, because you are "constraining" it (compressing it) - so very much. That's why compressors are almost always equipped with a powerful gain control marked "Output" or "Gain make-up" in order to boost the volume level back up to a reasonable level after it has been "squashed" down. 
Every time you turn the "Threshold" down, you are "constraining" the sound more and more, and making it quieter, and so you almost always need to use the "Output" control to boost the level back up again. This is a bit irritating, so several compressors have a switch - normally marked something like "Auto gain make-up" or similar - to automatically boost the output as you turn the "Threshold" down. It's not on every compressor, but it is a nice little feature to have, and saves you fiddling about with the "Output" control all the time. For clarity in the following examples though, I have assumed you either don't have this switch, or that it is turned off. 
So far so good. "Threshold", "Ratio", and "Output" are the main controls on an compressor, and "theoretically" give you everything you need. So what are the other controls for? 
Well, sometimes - in the real world - things aren't quite so simple. For example, you can have a vocal that is sometimes too quiet, sometimes too loud, and occasionally, way, way, way, way too loud. Wouldn't it be nice if the compressor somehow had an automatic "Ratio" control? 
That's why many compressors have a "soft-knee" or "over-easy" control. With the "soft-knee" control turned on, the compressor doesn't simply and immediately "kick-in" at the level set by the "Threshold" control - it merely "starts" to work. As the level gets louder and louder, it reaches a level where it is finally reaching the "power" of compression that is set by the "Ratio" control. 
So if you wanted to control a vocal that was wildy out-of-control in terms of levels, you could switch on the "soft-knee" control, set a "Ratio" much higher than normal, and set the "Threshold" control to the quietest "acceptable" vocal sound level. When the vocal exceeds this level with the "Soft-knee" control switched on, the compressor starts to compress at fairly moderate levels. If however, the vocal gets wildly out of control and attempts to get *seriously* loud, then the compressor starts working much harder to pull it back to sensible levels. It's a bit like having an automatic "Ratio" control, with the maximum compression "power" controlled by the setting of the "Ratio" knob on the front panel. 
Then there are the "Attack" and "Release" controls. So what do these do? 
If you've followed this explanation so far, you'll realise that a compressor is a bit like having a smart guy hanging onto a volume control and adjusting it by hand according to the music. But how quickly can this "person" respond? Well, the "Attack" control, adjusts how quickly this "person" is, at turning down the volume when things get too loud. The "Release" control is how quickly that same "person" can turn the volume back up again when things have calmed down. 
But why would you want to adjust this? Surely you would want it to be instantaneous? (after all, it *is* supposed to by an automatic system...) 
It turns out that in practice, in many situations, you don't want the volume to be "instantly" cranked down the moment things get too loud. Under certain conditions you can really *hear* the volume being pulled down, and this is very undesireable. Instead, it *sometimes* sounds better if the "person" is a bit sloppy and slow at yanking the volume down. The "Attack" control affects this sloppyness. 
What about the "Release" control? Well, in a similar way, if the compressor is too fast at turning the volume control back up again, you can hear it working (the audible effect is known as "pumping"). It just sounds "artificial". So the "Release" control adjusts the speed at which the compressor "recovers" after yanking down the volume. The exact speed which sounds "correct" depends on the music, so that's why you can adjust it by hand. The examples following in a moment give some suggested settings, but by all means experiment in order to find the most "natural" sounding setting. 
And that leads us to another control. It is a switch, and it is sometimes marked "Automatic" and sometimes marked "Peak/RMS". So what does this switch do? 
Well, as I mentioned before, the "Attack" and "Release" settings really depend on the music you are using the compressor on. But music continually changes. What the "Automatic" or "Peak/RMS" switch does, is to switch on an automatic setting that attempts to "listen" to the music and continually set the correct "Attack" and "Release" settings for you. Of course it doesn't always do the best job, and that is why you also have manual control if you want it. It is important to realise that with this switch turned on, the "Attack" and "Release" controls are disabled and will do nothing. Some compressors (unfortunately) don't have "Attack" and "Release" controls at all, and are either set to preset values, or permanently set to RMS (automatic). 
There is also an IN/OUT switch (often marked BYPASS). This is essential. It is there so you can switch the compressing action on and off and thus hear the difference your changes have made. To make best use of this switch, you need to set the "Output" control such that the sound appears to be at roughly the same level irrespective of whether the compressor is switched IN or OUT - this allows you to easilly make comparisons by listening. 
The final control on most stereo or two-channel compressors is called "Link". What is this for? 
Whenever you adjust the volume control on a stereo mix, you always expect both left and right volume levels to change at the same time don't you? (otherwise the mix would wander off to one side or the other). That's what the "Link" control is for. It makes sure that both left and right hand volumes always change in time with each other, so the mix stays "in the middle". 
As an added bonus, the "Link" control *usually* (although, not always) disables one set of compressor controls on a two-channel unit, and takes all of its settings from just one set of controls. This is because on a stereo signal you normally want *exactly* the same settings on both sides - as well as keeping the volume levels equal. This is not the case on all compressors though, so it is important that you check your manual to find out whether you need to set the controls on both channels to be the same, or whether you only need to use one set of controls (the other ones being disabled). 
On some compressors, even if one set of controls is disabled, the "Output" controls for each side may be independant (don't ask me why - it does seem a bit silly) - again, you *must* check the manual, as it is not always easy to tell simply by playing with the settings and listening. 
That completes our "tour" of the controls. I hope you understood it. Read it a couple of more times if you don't, and if you're still feeling lost, perhaps it might come to you after you've tried these examples. 
So: Now onto the examples... 
*Example 1: Hard Limiting*

The problem: You are doing a live gig or an important digital recording. You want to leave the music completely untouched, but what you don't want, is totally unexpected loud peaks causing damage or distortion. 
The solution: You want to stop TOTALLY any music or sound exceeding your expected maximum level. This is an emergency situation! But this is also quite simple to do with a compressor. Set the "Attack" and "Release" controls to their fastest - after all, it will only "kick-in" during cases of emergency, and you want it to respond immediately (to prevent distortion), and you also want it to recover immediately (so no-one notices anything happened). Make sure that any "Automatic" or "Peak/RMS" switch is turned off - so that the "Attack" and "Release" controls actually work and are not in automatic mode. The "over-easy" or "soft-knee" switch (if present) should be turned off too. 
Then set the "Threshold" control to maximum (probably marked +10Db or +20Db, but on some digital plugins it may be marked as zero). This will prevent the compressor doing anything just yet. 
Then set the "Ratio" control to maximum (normally marked 20:1 or even infinity-to-one). You won't hear anything happening just yet, because the "Threshold" control is set to maximum - effectively bypassing the unit. 
Now, play the LOUDEST MUSIC SIGNAL YOU EVER EXPECT TO HEAR through the compressor, and look at the levels. 
Now, slowly turn down the "Threshold" control, carefully listening and looking at the levels. The moment you even *start* to hear a decrease in volume or see it on the meters then stop, and back off a tiny bit. You have found your optimum settings. 
Just to check, try playing some excessively loud music through the compressor. You will find that it refuses to exceed the maximum level you have set, no matter how loud the input! 
Needless to say, if you get a bit silly and try to blast the compressor with INCREDIBLY loud music, you may indeed hear the compressor start to distort (it still won't exceed that maximum level though!). But this is just unrealistic. You are setting it up to handle only the most unusual, unexpected and extreme cases, which will be well below the level of distortion. 
*Example 2: Compression of an Instrument or Vocal*

The problem: You are working with a fairly good vocalist. Normally when they sing loudly everything is fine - but every now and again they sing their little heart out so much that the recording either distorts, or is simply just way too loud. Unfortunately the vocalist is so unpredicatable that when this happens you don't have time to adjust the recording levels because it happens almost at random, and is difficult to predict. 
The solution: An ideal application for a compressor! Start with a good recording level for normal recording, and with a fast "Attack" and a moderately slow "Release" on the compressor (ensuring these controls are on a "manual" setting). Also switch ON the "Over-easy" or "Soft-knee" button (if the compressor has one). 
As before, begin with both the "Threshold" and "Ratio" at maximum. Whilst the vocalist is singing at a fairly QUIET to moderate level, slowly turn down the "Threshold" control until either your ears or the meters detect the slightest faint drop in level. If your compressor has a "Gain reduction" meter it should *just* begin to indicate a change. Turn up the "Output" control until the quiet part is at a good level for you. 
Now go to the LOUDEST part of the song and get the vocalist to sing (or play back a recording). With the ratio at maximum, you should now find that - ironically - the sound is far too quiet! Simply turn the ratio control down until the level is just about as loud as seems reasonable. The "Gain reduction" meter - if you have one - will probably be lighting up lots of pretty lamps at this point (unless it is just a boring moving pointer  
As a final pass on this example, you might want to get the artist to perform the song once through (or playback a "take" if you are compressing on playback), and at this point you might want to play with the "Attack" or "Release" settings to get the most "natural" sound. Be careful if choosing an slow "Attack" though, as it might allow the compressor to "overshoot" and exceed the levels which you so carefully set previously. 
*Example 3: Adding "Punch" to a Sound*

(normally bass instruments like bass guitar or bass drum) 
The problem: The artist is performing a fairly rhythmic pattern, but somehow they don't seem to be "punching" through the mix, even though their sound is basically quite good. Every time they play a riff you know you really want to "feel" the "impact" - but it is simply not there. 
The solution: Although compressors are normally associated with *reducing* peak levels, did you know that they are capable of actually GENERATING amazing peaks? 
This technique generally only works with "percussive" sounding instruments like drums, guitar (including bass), and spiky keyboard sounds like "clavinet", that are playing a rhythmically "pulsating" part. 
The technique relies on the fact that the "Attack" control can be used to make the compressor respond in a sloppy way - thereby allowing lound signals to "overshoot" and generate peaks that weren't even there in the first place! 
To do this, start with a moderately slow release, a SLOW attack, and with the ratio and threshold at maximum. The "Soft-knee" or "Over-easy" control (if present) should be OFF. 
Play back the quietest part of the performance, and as before, turn down the "Threshold" gradually. You should find a setting where although the instrument is starting to get a bit quieter, it is starting to have more "punch" to it. Use the "Output" control to restore the level to a good volume. 
Now go to the loudest part of the song. You will find at these settings that the instrument is - surpringly - too quiet. Turn down the ratio until the sound is loud enough. 
Now check out the quiet part of the song again. You might now find that it is not as punchy anymore, and you might have to turn down the "Threshold" some more (and of course boost the "Output" to compensate). 
Finally, rehearse the part (or playback), and adjust the "Attack" to give you the "punchiness" you need overall. 
The "Release" control is quite critical in this scenario too. If you have it set too fast, you can hear the compressor "breathing" or "pumping" (you'll know what I mean when you hear it!). On the other hand, if you set "Release" too slow, then you will start to lose the "punchiness" - it is a tricky balance. 
*Example 4: Compressing a Final Mix*

Ooooh! This is the trickiest one of the bunch! You will probably have one of two problems. Either (a) the mix overall doesn't sound "punchy" enough - which requires slightly different settings to the previous example, OR - (b) you have the more common problem - you simply can't get your mix to sound "loud" enough compared to other recordings that you have in your collection. 
The problem (a): The mix overall doesn't sound "punchy" enough 
The solution (a): If your mix doesn't sound punchy enough you have to start with some "preset" settings on your compressor as follows: 
Start with the "Automatic" or "Peak/RMS" switch turned ON (RMS setting). Music is a complex thing, and a "final mix" even more so. The "Automatic" or "RMS" setting will literally "listen" to your music and try to find the "ideal" settings for both the "Attack" and "Release" controls and disable them. If your compressor doesn't have an "Automatic" or "RMS" setting, then set both the "Attack" and "Release" settings to medium. In both cases we will end up adjusting them manually later so don't worry too much. 
Set (as before), the "Threshold" setting to maximum (which "bypasses" the compressor), but this time pre-set the "Ratio" control to about 3:1 or thereabouts. Now, whilst playing the mix gradually turn down the "Threshold" level until you start to get a more punchy sound. You will (as always) have to turn up the output to compensate. 
When you can hear the compressor making a difference, try experimenting with the "Attack" and "Release" settings. If you previously set "RMS" or "Automatic" ON, then try to match both "Attack" and "Release" to the same sound as "Automatic" and use that as your starting point. The slower the "Attack" the longer the overshoot. Sometimes a short attack will sound good (making quick transients), other times, a slower attack will sound more appropriate. 
It's a good idea to go around ALL the controls in turn, making slight changes until you believe that you have the best settings on all of them. Use the IN/OUT button to compare results with the original - using the "Output" control to match the sound level between the IN and OUT settings, so they are at the same volume - this greatly helps make a good comparison. 
The problem (b): You can't get your mix to sound "loud" enough compared to other recordings 
The solution (b): You really need TWO sorts of compression here. Firstly, you need "limiting" set up as per example (1) previously. Turn down the "Threshold" until you can start to hear the limiter making an unpleasant difference to the mix. Then turn it back up a bit, and try to find the position where you have the best balance between cutting down the peaks, and making an undesireable change to the music. In most cases it should be possible to apply quite a lot of limiting without any significant difference to the sound of the track. 
Now that you have trimmed off the peaks, you can crank up the "Output" to a much more respectable level for mastering on CD. But you might want your CD to sound louder still. If that's the case, then apply another compressor BEFORE the limiter and just try some conventional compression as in solution (b) above (but probably with a faster attack). Many mastering compressors have a compressor AND a limiter combined in one unit for this very purpose. 
As an alternative approach, set quite a fierce compression (5:1 or more), and switch on the "over-easy" or "soft-knee" button, and with fast attack. Start (as always) with the "Threshold" high, and slowly turn it down until you achieve the balance between a good amount of compression, and best sound quality. Adjust the "Release" control to help minimise how much you can "hear" the compressor working. The speed of "Release" setting is different depending on the speed and type of music - let your ears judge it. 
That concludes our four main examples. 
*Advanced Use*

Most analog compressors have a "Side-chain" socket on the back, and now some plugins are offering a similar facility too. So what's it for? 
The compressor works by feeding the sound through the compressor itself, but also by feeding the sound to the compressor "control system". The control system "listens" to the sound and controls the compressor volume. 
The side-chain is a system that lets you insert something - like a graphic equaliser for example - immediately before the compressors control system. Note this is NOT in the main audio path and doesn't affect the sound as such - just the way the compressor responds. This system lets you over-emphasise a certain frequency that you want the compressor to listen out for. For example: 
*Example 5: De-essing a Vocal*

The problem: You have a vocal, but sounds such as the letters "S" and "T" are sounding really harsh, and burst through the mix too much. You don't want to equalise them out of the vocal sound, because the vocal sound is actually quite nice apart from those explosive "S" and "T" sounds. 
The solution: Using fast "Attack" and quite fast "Release", set the compressor at about 3:1 and then place an equaliser into the side-chain. Suck out all bottom end, and middle, and apply a boost at around 3 to 6KHz. You will find that adjusting the "Threshold" will control how powerful the "S" and "T" sounds can get. Overdo it and the vocal can sound very strange. Set it so that it gets the "S" and "T" sounds just how you like them. 
Note: It is understandable to think that you might need two compressors on a vocal - one to perform de-essing, followed by another one doing "normal" compression. This is not so. One compressor can do the two jobs at the same time! Simply compress the vocal as normal. Then insert an equaliser into the side chain, and apply a small boost around the sibilant region (around 3KHz-6KHz). This will cause the compressor to over-react on sibilant sounds, thereby de-essing at the same time as compressing. Use the EQ BOOST to control how much sibilant sounds are CUT. 
It is VERY, VERY IMPORTANT not to overdo de-essing. If you do, the singer will sound like they have a lisp. Or should that be lithp?  In any case, once you've screwed it up by overdoing it during recording, then there is little you can do to rescue it later - so go easy on it! (you can always de-ess some more during mixing if required). 
It's important to understand that the equaliser you choose to place in the side-chain does NOT affect the frequency response of the sound going THROUGH the compressor, just what the compressor internally LISTENS to. It therefore effects how the overall volume responds to changes in volume at certain frequencies. This is known as "Frequency SENSITIVE compression". It is also possible to purchase more complex compressors that actually DO affect the frequency response in different bands, and this is known as "Frequency SELECTIVE" compression - there is a big difference between the two, although the names are similar, and even professionals get the two terms mixed up sometimes. 
The example above isn't the only use for the side-chain - and indeed you don't even have to feed the same sound into the side-chain as you are feeding into the main input. You could for example feed the sound of your voice into the side-chain. In that way you can create a system that automatically fades down music when you speak, and fades it back up when you stop speaking - the same feature that some disco consoles have - except you have full control over the fade in/out rates using the "Attack" and "Release" controls. 
In a similar way, you could feed the reverb returns from your lead vocal reverb through the compressor, but plug the dry vocal into the side-chain. That gives you a system where the reverb fades down when the vocalist sings, giving quite a "dry" sound, but returns to a strong "wet" reverb inbetween words and phrases in the song. It keeps the reverb from messing up the vocal in the parts when the words get busy. Such a technique is also useful for controlling the level of repeat "echo" effects at the end of phrases. 
*Summary*

In all of the above examples, the settings and approaches suggested are merely a guide. Your best teacher of compression is your own ears, and the compressors that you own. When you find a setting that really works on a certain instrument, write it down - it will save you a lot of time later when you next record that same instrument. You need to work with your compressor for a long time, and develop a good working relationship with it, until you can really trust what it is up to. 
Every model of compressor on sale sounds different. That's why people talk with great affection about certain old valve compressors, or perhaps a particular model of DBX compressor that they love (DBX are the world leaders in sound compression harware, and make by far most of the chips in the world that achieve it. This means that many compressors not even made by DBX, often contain DBX chips at the center inside them). 
Settings vary between equipment. A setting that sounds great on one compressor, often sounds terrible on another. This applies to software plugins too, which is surprising, as one would expect the maths and figures to be identical in each one. 
The fact that people have a personal preference for different types of compressed sound, means that there will always be a market for compressors from different manufacturers. There will always be the "classic" compressors that almost everyone likes, and there will also be a number of obscure quirky units and plugins that only appeal to a select few. 
Compression is an extremely difficult thing to describe in writing, and you really need to hear compression - in all its different forms - to get an understanding of how it can help you. Never apply compression to something simply because other people do. Apply it because you KNOW that you really NEED it and that you UNDERSTAND exactly what it is DOING to the sound. If in doubt, compress too little rather than too much (it is very difficult - indeed, often impossible - to undo bad compression later), and remember that too little compression during recording can always be made up for when mixing later (at the expense of a little quality). 
As always, practice makes perfect, and I hope that this article has gone some way towards demystifying the process for you. 
[/FONT]


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## Ambit

Im self-sufficient in mixing, but I have not really played around with mastering too much, all of my songs are only mixed except for this one which isn't really a guitar oriented song but it IS mastered.... Ides (Instrumental) by MikeIsMe on SoundCloud - Create, record and share your sounds for free But anyways, if I am already very satisfied with the mix, what do I add to the master? I understand that compression is used in a master but I'm not sure what ratios and stuff to start at to begin playing around with it...


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## ShadowAMD

manana said:


> Why is it a bad idea to eq before comp? Wouldnt you want to get rid of the unwanted frequencies first?


 
It's not a bad idea, it can be more difficult to work with.. Less is more in mixing in many cases and every time you change EQ you have to adjust settings on the comp to match.

Sometimes you have to do PRE EQ, let's say you get a singer tapping on a stand, it might cause the compressor to suddenly duck in places due to LF boom. So in that case you would have to HPF before the compressor... 

But still after that I would reccomend the HPF then the compressor and another EQ plug..

It will make life easier.


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## noodle6491

Nothing useful to add, I'd just like to give out a massive thanks to all you guys because this thread has been silly useful. I knew basically next to nothing about compression before, and now my sounds are on their way to improved happiness.


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## GatherTheArsenal

Big time kudos to all who contributed to this thread  been struggling trying to understand compression and wrap my head around it, this is helping a lot! Cheers.


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## imaginary

manana said:


> Why is it a bad idea to eq before comp? Wouldnt you want to get rid of the unwanted frequencies first?



This is a good question. I saw two responses to this agreeing to EQ then Compress. I also agree.

Here is my case. I recorded two albums in the same studio. I used an old Marshall Head through a jcm800 4x12 cab. That cab has a killer low end resonance. It sounds bad ass and totally killer. I love it. The engineer was like,"way too much bass!". And I was like,"no,no,no please let me keep it I love it, f*&k the mix and f&%k everybody else in the band!"... So, we tried to keep it. But, I know nothing and I didn't want to ruin the album so we decided to run a high-pass filter on the guitars. A good choice... Except for that the cab mics went straight into a Joe Meek compressor before hitting the board! All my tracks were recorded compressed already. I agree. The high-passed guitars fit the mix better. But, they also sounded pretty wimpy. The worst damage was, our palm mute sections disappeared! Into nothingness. What is metal without palm mute sections?

It was an expensive learning experience for me, so I'm passing it on.

Here is what happened. Especially in the case of the palm mute sections, the wicked low end resonance was pumping that compressor big time. The Joe Meek is not a multi-band compressor, so that big low end resonance causes the compressor to lower the gain of ALL frequencies. Once the high-pass filter was engaged, the very frequency range that was pumping the compressor, wasn't even there anymore. What was left was getting compressed, even though it wasn't guilty of being loud!

The second album we High passed the cab mics, THEN compressed them. the guitars were so much more fierce and... the palm mutes could not only be heard, but pleased me very much


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## Sferic

Guys, any simple tips/recommendations for side-chaining/ducking to get that "eardrum overload" sound? Strapping Young Lad's track "Love?" comes to mind as an example of the effect.


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## DavePiatek

Vince said:


> important fact I learned today....
> 
> When mixing drums, apparently compression should come before the EQ.



Not necessarily. If I'm compressing a snare, and I'm trying to notch out a nasty ring, it's WAY easier to get it sounding good if I notch before the compressor. My rule of thumb is narrow cuts = before compressor, boosts = post compressor.


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## BrandyWalch

Im new to recording and mixing and I'd just like to say I think having a thread like this is really great and incredibly useful


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## DavePiatek

This might help some folks who are trying to tackle drum compression

https://www.youtube.com/watch?v=aBG4xvlq6gM


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## thedukewestern

yes travis you are right. Dynamic range and level can be considered the same thing - however we use these two phrases as they refer to two different points in our signal chain when using compression. 

heres a couple of quick pointers to help out.

1) if your having trouble hearing what your compressor is doing to a track - crank down on the threshold untill you are clearly overdoing it - this will really shed light on all of your attack, release, and ratio settings and help you really understand how these will effect your work.

its very common to use eq before and after a compressor for the following reason. The EQ in front of compression can be useful for corrective purposes: a Hi Pass filter, pulling out a ring in a tom, a singer who is a ittle too close to a mic and theres some proximity effect low end, a brittle pick attack on an acoustic.. or finger slides on wound strings. The reason for this is to clean things up the way you want - if needed - before you compress the whole thing and bring it forward with compression. 

An eq after this would be used in say to add aesthetic choices. Usually a high/low shelf where we can make the now much more sonically focused track sit in the mix how we desire. 

simple way of thinking about it - Cut before comp - boost after.


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## col

Here's a good show about compression: BBC Radio 4 - Compression versus Art


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