Gating and Compression for n00bs

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kcearl

I see deaf people
Number 2 in a series of none lol :)


didnt find any copywrite on this so its unaltered


Guide To Gating

by Trevor Curwen


Basic operation

A gate's basic function is to remove unwanted noise between the sections of wanted material. It is usually connected via a mixing desk's channel insert points or in-line with the sound source so the whole signal passes through it. In live sound applications gates are used primarily on drums to ensure each individual drum's mic picks up sound from that drum only. In recording applications, using a gate while actually recording can be dangerous as you could accidentally gate out part of the performance. Therefore, gates are more likely used at mixdown.

A typical example of a gate's more conventional role is to clean up an individual track of a multitrack recording. If, say, a recording of a miked up guitar amp has amplifier hiss plus low -level bleed from other instruments, the gate could be used to shut down the track when the guitar isn't playing so the unwanted sound won't clutter up the mix.
At its simplest, a gate acts as an automatic switch, separating the louder sounds from the quieter ones. You can set a threshold above which sound is kept, and below which it is rejected. The sound to be treated - known as the
program material - is fed into the noisegate's channel input and the gate will remain closed, effectively silencing the sound until it rises above the threshold and opens the gate.
The action of the gate is determined by its sidechain circuitry. In normal use this is fed by a split of the signal from the input, known as the key signal. The circuitry senses the strength of the incoming signal and when the signal
exceeds the threshold, the sidechain circuitry opens the gate.

Open the envelope


How quickly the gate opens and closes and how long it remains open is set by its envelope controls. The attack control sets how quickly the gate opens after the threshold has been reached. In the majority of cases a fast
attack time will be the norm, but the attack control can also be used as a creative tool; by setting a slow time sounds will swell in slowly for a 'bowed' effect. The hold control keeps the gate open for a preset time after the
signal has passed the threshold and the decay control sets how quickly the gate closes once the signal has dropped below the threshold level.
All three envelope controls are usually found on dedicated noisegates but some basic gates, especially those found in channel strip type units alongside other processing, have more limited control or envelopes that are set automatically depending on the program material.
A rudimentary gate's sidechain senses level changes alone, but a more fully specified gate such as the industry standard Drawmer DS201 has key filters that can be used in conjunction with the threshold control to prevent
sounds that fall outside a set frequency range from opening the gate. Filtering usually involves rolling off high and low frequencies to zero in on the wanted sound and eliminate as much of the unwanted sound as possible. It is only applied to the sidechain key signal and not to the program material, which remains unaffected. By putting the gate in Key Listen mode, which routes the key signal directly to the output, the effect of the filters can be heardwhile you adjust them.

A typical example of using the filters would be when using multiple mics on a drumkit. You may want to gate a particular drum, say the snare, but are having problems because the hi -hats bleed into the snare mic and are
opening the gate. A gate opens whenever the incoming signal exceeds the set threshold, so reducing the threshold level goes some way to helping this problem but you run the risk of gating out some of the quieter snare
hits. Hi-hats inhabit a higher frequency range than snares, so bringing the filters into play in this instance and rolling off the top end will allow you to reduce or eliminate the possibility of a hi -hat opening the gate.
This technique can also be used to separate the kick or snare in a drum loop so it can undergo further processing or EQ before mixing it back in with the original to change the sound of the loop. If you have no need to use a gate
in a gating role you can use the filters purely to EQ any signal passing through it. To do this, just put the gate in its Key listen mode. The filters can now be used to merely remove a little top, bottom or both from the signal or to severely limit its bandwidth.
Finally, the range control determines how much signal can be heard when a gate is closed. For many applications, setting the range to its extreme setting so that the closed gate totally silences the sound would be
the norm but in some circumstances this may sound unnatural, so the control can be adjusted to ensure the sound is only attenuated to a set level when the gate closes.

External key

Some of the more unusual effects gates can be used for are achieved by using one signal to gate another. A gate's sidechain circuitry can be switched, so that instead of sensing the strength of the incoming (internal) signal entering the channel input it will sense the strength of any external signal plugged into the gate's key input, a socket usually situated on the rear panel.
With a gate's key source switch set to External mode, any signal present at the key input, as long as it is above the threshold level, will open the gate, making it possible to use this key input as a 'switch' to open and shut the
gate regardless of the characteristics of the program material being put through the unit. This feature can be used to add an extra element of sound to certain drum hits and is the way to add real gated reverb, if that's your thing. To add reverb to specific snare hits on a recorded drumkit, a track of the room ambience recorded by a distant mic is used as the gate's program material. A split from the snare drum signal is then patched into the key input so the gate opens for a burst of ambience every time the snare hits. The sound of the ambience can be shaped using the envelope controls.
The same basic technique can be used to add some real low end into a weak bass drum sound. This technique may not be too relevant to anyone sequencing a bass drum as there is always the option of using whatever
sample you wish, but for a live recorded bass drum it's a different matter. The trick is to have a deep continuous sine wave such as those produced by Akai samplers as the gate's program material and use a version of the
existing bass drum at the key input.
The gate will open every time the bass drum plays, creating a low bass note that, with carefully set hold and release settings, can be mixed in with the original bass drum.

Ducking

Ducking is another gate function that relies on the key input for its implementation. Everybody who listens to the radio will hear ducking in action at some time or other when the music is made to drop in level whenever the DJ speaks over it. This is achieved by having the music as the gate's program material and taking a feed from the DJ's microphone signal into the key input of the gate. If the gate was set up for normal gating it would open when the DJ started talking, but in Duck mode the gate's action is reversed so it closes when faced with a key input signal. The degree to which the gate closes is set by the range control and this can be adjusted to create a subtle drop in level if required.
From a musical point of view, this can give a rudimentary automation of an instrument's volume. Take the example where a synth pad is playing as part of a backing track but needs to drop slightly in volume to make
space for vocals. This can be achieved by putting the pad through the gate and feeding a version of the vocal into the key input. Whenever the vocalist is singing the pad will drop in volume and the gate's envelope controls can
be set so that it fades back up at the end of the vocal phrase.

A similar thing can be done with effects. If the effects returns are fed through the gate, any reverb or delay can be subdued while the vocal is present only to swell back up at the end of phrases.
 
Understanding Compressors and Compression

from an article by Barry Rudolph


A compressor consists of four basic parameters:


Ratio


Ratio is a way to express the degree to which the compressor is reducing dynamic range. Ratio indicates the difference between the signal increase coming into the compressor and the increase at the output level. A ratio of 10:1 would mean that it would take an increase of 10 dB coming into the compressor to cause the output to only increase 1 dB. Ratio is a constant value, as it doesn't matter how much compression is taking place; the ratio of the input change to output change is always the same. Compressors and limiters are really separated only by a loose definition: Generally, compressors have compression ratios up to 8:1, while limiters have ratios higher than 8:1. Most professional compressors have either fixed selectable ratios (such as UREI's 1176 with presets of 4:1, 8:1, 12:1 and 20:1) or continuous variable
ratios (such as the dbx line of professional compressors).
Some recent compressor designs instantaneously change ratio depending on the program's dynamic content and the constraints of the front panel control
settings.


Threshold

Threshold is the level of the incoming signal at which the compressor amplifier changes from a unity gain amplifier (like a straight piece of wire, theoretically) into a compressor reducing gain. The compressor has no effect on the signal below the threshold level setting. Once threshold is reached, the compressor starts reducing gain according to the amount the signal exceeds threshold and according to the ratio control setting. Threshold level could be thought of as the "sensitivity" of the compressor and is expressed as a specific level in dB. The exact moment the compressor starts gain reduction is called the "knee."
"Hard knee" compression describes this moment as sudden and certain. "Soft knee" or smooth knee compression is a less obtrusive change from simple
amplifier to compressor. Soft knee widens or broadens the range of threshold values necessary for the onset of compression. On quality compressors you can switch between hard and soft knee compression. The amount of gain reduction is measured and read on a standard VU meter whose needle rests on the 0 VU mark. The needle will deflect negatively downward to indicate how much gain reduction is occurring in dB. VU meters are RMS or average level responding and do not indicate fast or peak gain changes. LEDs are also used for VU meters, and they will better indicate peak levels. A well-designed
compressor will have a good meter that reads input level, output level, gain reduction and any excessive peak output with an LED clip indicator. Once the amount of gain reduction is determined, the recording or operating
level is readjusted with the output or make-up gain control on the compressor.

Attack

Attack time refers to the time it takes the compressor to start compressing after threshold has been reached. Typical attack times range from less than
1 millisecond at the fastest to more than 100 milliseconds at the slowest. Attack time settings affect the sound quality in terms of overall perceived brightness or high-frequency content. If you use very fast attack time settings, the compressor will activate very quickly, reducing gain instantly at the waveform level of the sound. Since transient information at the front or attack portion conveys brightness character, especially with percussive sounds, immediately reducing it with the compressor will dull the sound. Selecting a slower attack time will allow the transient portion of the sound to pass through before the compressor starts clamping. However, if the attack time is too slow, ineffective and tardy compressor action may result.
If you compress a snare drum track with a fast attack, you may notice a diminished or shortened attack of the front portion of the snare drum sound. Instead of a good "hit" at the beginning, you will hear a very short "blip." If
the attack time were even faster, you wouldn't hear any snare attack at all. Adjusting the attack control to a slightly slower attack time will lengthen this blip back to the original snare attack length. Engineers use a compressor to get more attack out of a snare drum by using a low threshold and a high ratio. After making up gain with the output level control of the compressor, the attack portion ends up greatly amplified just before the compressor starts squashing the trailing portion of the snare drum sound. I like to mix this "twacked" sound with the original un-processed snare drum track.

Release

Release time is the time the compressor uses to return to unity gain after the input signal has fallen below threshold. The compressor is said to "release" from gain reduction. Typical release times on popular compressors go from as fast as 20 milliseconds to over 5 seconds. Most engineers envision their compressors doing their job of gain reduction quickly
and then releasing quickly to get out of the way. For the most part this holds up for pop recordings, but super fast release times, along with a fast attack time setting, will distort low-frequency sounds, as the compressor is capable of gain change within the period of the sound's waveform. You can demonstrate this by using a very fast release on a bass guitar compressor and have the player play loud and sustained notes. Over-long release time settings are another form of distortion, since gain reduction is "stuck" clamping the sound down for an unnaturally long time. "Pumping" and "breathing" are engineer jargon words for obvious compressor artifacts or side effects with maximum compression. Sudden and usually unwanted
deep gain reduction is called pumping, while a slower return (release) to operating level with a noticeable rise of the noise floor is called breathing. Newer compressor designs have clever predictive and adaptive schemes that reduce these side effects, making the compressor's action nearly undetectable or at least tolerable in most intense gain reduction situations.
 
Using Compressors in music


Trying to arrive at proper recording level can be like chasing a moving target, especially if you are working with inexperienced musicians or singers. It is easy to just "pack" the signal from a widely dynamic singer into a compressor, crank it way up and call it a day! On the other hand, the creative and caring engineer may use an equalizer in the sidechain of a compressor to selectively compress certain problem frequencies of the singer's voice. The sidechain input is a direct path to the compressor's detector circuitry, where an external signal can also trigger compressor action. Using an equalizer in the sidechain makes the compressor more (or less) sensitive to sounds within the EQ's frequency passband. Other sidechain compressor applications are de-essing and ducking. De-essing is accomplished by connecting an equalizer to the sidechain of a peak limiter and boosting, with a medium to high Q, the "s" frequencies anywhere from 1.5 to 6 kHz (depending on the singer). Strong "s" sounds are quickly reduced
without (one hopes) too much consequence to the rest of the vocal sound's signal. Ducking is gain reduction that is triggered from a different audio source altogether. The most common usage is to "duck" or lower a music bed (track) whenever a narrative voice-over is active.


Bass guitar

Generally, bass guitars seem to sound better when using some compression. I sometimes rely on the compressor to pull up some additional bottom end and warmth. I like to use a leveling amplifier for bass guitar such as an LA-2, Anthony DeMaria Labs or a Tube-Tech CL-1B compressor set up as a leveling amp. Based on the song's tempo and/or the bass player's style of playing, I might start with ratios of 5:1 with a medium threshold setting, medium attack and a slower release time. Unless you are looking for a pumpy effect or have a very wild bass player that the producer would like to squash, I rarely compress bass guitar more than about 5 dB max VU.


Vocals


A lot of anguish and pain surround the recording of vocals. Maybe some singer
insecurities, producer apprehensions and overall great expectations weigh on the arrival of a stellar vocal sound. It's about preferences, and vocal sound is subjective and contextual within the backing track. It does not exist on its own unless you are recording an a cappella performance. What I might think is a great vocal recording on a certain CD may be not be what the singer and producer are looking for to convey the emotional import of the artist, the song's lyric or the vibe of the song. At the first vocal recording session, you will want a starting point vocal sound that fits the singer, the song and the production. This starting point sound will work well to capture the immediacy of the moment and hold up later in mixdown. After mic selection, mic preamp selection and EQ setting, a compressor type is decided. Although there is much interaction between all these components, my starting point settings are predicated upon a +4dB level coming from this mic/preamp/EQ chain. For vocals, I tend to use compressors with adjustable attack and release time controls. I like tube-based compressors, although for more difficult control problems I would go to a VCA-based unit. If you were to set the threshold at
about 0 dB, the ratio at 4:1, the attack and release at middle positions and adjust the output level for a good recording level, you'd have about 3 to 6 dB of compression and probably make most people happy. This is just a good starting point, and you should get in there and change those settings to your own taste.


Stereo mix compression


A popular place to apply compression is on the entire stereo mix as it is going to the master tape. Stereo compression is also applied "after the fact," such as in mastering, but there is a big difference. If you are mixing your record into a compressor ahead of the master tape recorder (or DAW or whatever), then you are mixing many sources (tracks or elements), each with its individual dynamic content. Making mix moves (especially big gain
changes) directly affects the compressor's action, which, of course, affects the relationship of all the other mix elements, that is, the whole mix! If you do not use a stereo compressor at mix and compress at mastering, then you have just the dynamics of a 2-channel stereo mix for the compressor to react to. Many engineers and producers mix into a compressor and then have
the mastering engineer compress again, while others prefer to wait until mastering to compress digitally. A good starting place for the stereo mix compressor is a lower ratio with medium attack and release time settings. Set the threshold (and output level) so that you can hear an increase in level (average loudness) when you A/B the compressor in and out of circuit.


Remember, this is just a starting point! You may want to use a higher ratio to control peaks better and/or a lower threshold for more compression and denser overall finished sound.
 
no probs Steve..I never wrote it ;)


If there's anything else you can think of gimme a yell...I've collected tonnes of stuff scanned and PDF'd it...mostly aimed at a n00b level

Im thinking one on vocal recording next to go with Kim Lagoie's excellent blog
 
Vocal recording would be great. I always have trouble getting good vocal tracks. I usually just assume my gear is the biggest problem but the more I record the more I feel like I could get more out of it.
 
Any suggestions on how to compress distored metal guitar? I've done a lot of testing to get a good metal sound and I've never really liked the sound of compressors on the guitar. I play pretty heavy modern style metal and for some reason the compression always seems to deaden the sound too much. However, I've heard a lot of people swear by compression for metal guitar.
 
Any suggestions on how to compress distored metal guitar? I've done a lot of testing to get a good metal sound and I've never really liked the sound of compressors on the guitar. I play pretty heavy modern style metal and for some reason the compression always seems to deaden the sound too much. However, I've heard a lot of people swear by compression for metal guitar.

Heavy distortion is a form of compression in of itself, if you look at the wave form of distorted guitar it's usually pretty undynamic to start with.
Also are you using a compressor stomp at the begining of your guitar FX rig that is going to further level the signal

Post recording you could use a compressor to emphasize the punch of the guitar (at the expense of sustain) by setting a relatively long attack time and release time to taste.

If you have a short attack time then you will be further compressing an already fairly compressed signal which will leave it pretty lifeless in a lot of cases

Volume automation may give you more what you are looking for

Of course YMMV
 
Thanks for the help! I usually dont need a lot of sustain but I've heard a lot of people say it tightens up their guitar. Maybe I'll just have to mess around with it some more but I haven't like the sound yet.
 
Any suggestions on how to compress distored metal guitar? I've done a lot of testing to get a good metal sound and I've never really liked the sound of compressors on the guitar. I play pretty heavy modern style metal and for some reason the compression always seems to deaden the sound too much. However, I've heard a lot of people swear by compression for metal guitar.

In general I like compression before distortion so the sustain makes my distorted tone is more consistent. If you put the compressor after the distortion you can bring up parts where the guitar wasn't hitting the distortion as much, which usually sounds a little weird to me.
 
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