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Unread 07-27-2004, 04:55 PM   #1
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Lightbulb Know Lots About Compression:

Big List: Here.

Ripped from: samplecraze.com

------

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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Unread 07-27-2004, 04:56 PM   #2
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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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Unread 07-27-2004, 04:59 PM   #3
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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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Unread 02-14-2006, 08:20 PM   #4
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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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Unread 03-22-2006, 07:56 PM   #5
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Quote:
Originally Posted by desertdweller
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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Unread 06-10-2006, 11:14 AM   #6
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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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Unread 06-10-2006, 12:26 PM   #7
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Quote:
Originally Posted by 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?
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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Unread 10-07-2006, 01:50 PM   #8
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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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Unread 12-03-2006, 08:46 PM   #9
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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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Unread 01-11-2008, 04:12 PM   #10
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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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Unread 02-06-2008, 01:29 PM   #11
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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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Unread 02-03-2009, 03:21 PM   #12
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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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Unread 03-22-2009, 02:39 PM   #13
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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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Unread 03-23-2009, 01:24 PM   #14
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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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Unread 09-20-2009, 03:18 AM   #15
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<3 Compression

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Unread 11-16-2009, 02:33 AM   #16
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Thank you, all of you nearly made me understood compression ! Very interesting topic !
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Unread 12-24-2009, 12:09 AM   #17
 
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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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Unread 02-26-2010, 02:14 AM   #18
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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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Unread 06-23-2010, 08:46 PM   #19
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This will help me alot in my mixes, thankyou!
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Unread 06-24-2010, 12:36 AM   #20
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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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Unread 06-24-2010, 03:33 AM   #21
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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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Unread 10-09-2010, 03:07 PM   #22
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This site is killer info!
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Unread 12-24-2010, 11:26 PM   #23
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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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Unread 02-07-2011, 04:40 AM   #24
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I have heard good things about Bombardier.
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Unread 02-09-2011, 01:34 PM   #25
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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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