All About Bass Compressor

7/27/2019 All About Bass Compressor

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What is compression, and how do I use a compressor?

Please read these very useful articles, they explain everything with nice graphics:

From GuitarNoise.com

From Harmony Central

From Electronic Musician

From Mix Magazine

From Jim Carr

From Rane

A .pdf from dbx, "Compression 101"

A .pdf from TC Electronic, "Compressor Applications"

A .pdf from Rane, "Dynamics Processors"

A compressor is just an automatic volume control. At a basic level, it reacts to volume spikes from your

music, and turns down the volume a bit as your input levels go up. That's really all there is to it. The

reason compression is so widely misunderstood and confusing is because the various circuits that

actually do the volume control almost always have some other impact on the tone which you may like or

dislike, and also because it can honestly be quite difficult to set up any unit so it compresses your signal

enough but not too much.

People (including me) talk about compressors fattening their tone, increasing sustain, making their

sound "punchy", or other improvements; while those effects are possible, they are really just side

effects that maybe achieved, depending on your settings and the particular unit being used. But simply

putting a comp in your signal path will not necessarily give you any of those desired effects--you have to

make some educated choices.

You need to decide first which effects (such as sustain, peak limiting, or more consistent levels) you

want to achieve; and what you are willing to pay--or put up with--to get those results. One key thing to

know is that compression is always a compromise of some kind. Everycompressor, from the cheapest to

the most expensive, is a compromise. Selecting a compressor is largely about choosing the compromises

that work best for you. For example, if you want a compressor that can give you both a natural

transparent sound anda funky/dirty fat sound, be prepared to carry a rack unit that costs a lot of money

and has a dozen knobs. Or if you want something very simple to use, be prepared to accept the fact that

the sound and response of that simpler unit may not ideally match your instrument or your playing

style. If you want lots of sustain, understand that sustain usually comes with a lot of noise. For every

benefit there is a cost. But it's like anything else in life, the benefits are totally worth the trouble if you

choose wisely.

There are a few core elements to compression; once you understand them, you'll have an easier time

setting up anycompressor with your rig. In fact, to use a compressor well and get good results at all, you

must first familiarize yourself with these concepts:
http://www.guitarnoise.com/article.php?id=313http://www.guitarnoise.com/article.php?id=313http://www.guitarnoise.com/article.php?id=313http://www.harmony-central.com/Effects/Articles/Compression/http://www.harmony-central.com/Effects/Articles/Compression/http://www.harmony-central.com/Effects/Articles/Compression/http://emusician.com/mag/emusic_big_squeeze/index.htmlhttp://emusician.com/mag/emusic_big_squeeze/index.htmlhttp://emusician.com/mag/emusic_big_squeeze/index.htmlhttp://www.barryrudolph.com/mix/comp.htmlhttp://www.barryrudolph.com/mix/comp.htmlhttp://www.barryrudolph.com/mix/comp.htmlhttp://www.azwebpages.com/bass/basscompression.htmhttp://www.azwebpages.com/bass/basscompression.htmhttp://www.azwebpages.com/bass/basscompression.htmhttp://www.rane.com/note134.html#dynamicshttp://www.rane.com/note134.html#dynamicshttp://www.rane.com/note134.html#dynamicsftp://ftp.dbxpro.com/pub/PDFs/WhitePapers/Compression%20101.pdfftp://ftp.dbxpro.com/pub/PDFs/WhitePapers/Compression%20101.pdfftp://ftp.dbxpro.com/pub/PDFs/WhitePapers/Compression%20101.pdfhttp://www.harmony-central.com/Effects/Articles/Misc/compression-applications.pdfhttp://www.harmony-central.com/Effects/Articles/Misc/compression-applications.pdfhttp://www.harmony-central.com/Effects/Articles/Misc/compression-applications.pdfhttp://www.rane.com/pdf/ranenotes/Dynamics%20Processors.pdfhttp://www.rane.com/pdf/ranenotes/Dynamics%20Processors.pdfhttp://www.rane.com/pdf/ranenotes/Dynamics%20Processors.pdfhttp://www.rane.com/pdf/ranenotes/Dynamics%20Processors.pdfhttp://www.harmony-central.com/Effects/Articles/Misc/compression-applications.pdfftp://ftp.dbxpro.com/pub/PDFs/WhitePapers/Compression%20101.pdfhttp://www.rane.com/note134.html#dynamicshttp://www.azwebpages.com/bass/basscompression.htmhttp://www.barryrudolph.com/mix/comp.htmlhttp://emusician.com/mag/emusic_big_squeeze/index.htmlhttp://www.harmony-central.com/Effects/Articles/Compression/http://www.guitarnoise.com/article.php?id=313


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Input level is critical because it determines the range of signal that the compressor "hears" and reacts

to. Some comps don't have an input level control, so you'd have to use the output volume controls on

your instrument, preamp, or another pedal to regulate the level going into the compressor. Finding and

setting the correct input level is probably the number one problem that frustrates compressor pedal

users; the wrong levels will make your new pedal seem like a noisy waste of time.

Threshold is how loud your signal has to get before the compression kicks in. This is essential because

you may not want your entire signal to be compressed. Some units have no threshold knob- for them,

the threshold is "fixed" and can only be adjusted by changing the input level of your signal.

Ratio is how much your signal gets compressed once it passes the threshold. Ratios are figured in

decibels (dB); a dB is a unit of how much a signal increases or decreases relative to where it started.

With a ratio of 4:1 for example, the idea is that for every 4 dB your signal goes over the threshold, the

output level will only go up by 1 dB. Generally, ratios of 2:1 to 4:1 are considered light or moderate

compression, and ratios of 10:1 or higher are considered heavy compression or limiting. A hard "brick

wall" limiter has a ratio of infinity:1, meaning that once your signal crosses the threshold, the output will

not increase more than 1 dB no matter how high the input signal spikes.

Attack controls how quickly the compression reacts to your signal, and Release controls how long it

takes to "let up" and stop compressing after it's triggered. These controls are interactive, and the right

settings for them will vary depending on the music and your playing style. You'll have to experiment, but

a decent rule of thumb is to start with the attack and release knobs in their middle position, and adjust

from there.

Output Gain controls how much the volume of your signal is increased coming out of the comp, and

this is necessary because compression lowers the overall average levels of your signal. So almost all

compressors have a booster at the end, which provides "makeup gain" to bring your signal back up to

the level you want. This is what accounts for both the increase in audible sustain and harmonics, and

also the increase in the noise floor.

For compressors with only two knobs, "Compress" (or "Sustain") and "Level", the Level knob controls

the output gain, while the Compress knob may control the ratio, the threshold, or the gain of your signal

being boosted into a fixed threshold. It varies with different circuit designs, so you'll need to find out

which function it is for any specific pedal you're using.

Please seethis articlefor further discussion of how to set up each of these parameters, as well as an

explanation of "hard knee" versus "soft knee". And check outthis articleif you are still wondering

whether you even need a compressor at all.
http://www.ovnilab.com/articles/setup.shtmlhttp://www.ovnilab.com/articles/setup.shtmlhttp://www.ovnilab.com/articles/setup.shtmlhttp://www.ovnilab.com/articles/necessary.shtmlhttp://www.ovnilab.com/articles/necessary.shtmlhttp://www.ovnilab.com/articles/necessary.shtmlhttp://www.ovnilab.com/articles/necessary.shtmlhttp://www.ovnilab.com/articles/setup.shtml


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What is the difference between a compressor and a limiter?

Limiting is a type of compression- a limiter is a compressor. However not all compressors are limiters.

The primary deciding factor is that a very high ratio, typically 20:1 all the way to infinity:1, doesn't allow

much of your signal past the threshold- which limits the signal to a certain peak level. A lower ratio

allows a wider range of your signal past the threshold, compressing it but not capping it off so

extremely.

The threshold setting is also very important. When using a "limiter", typically you want to set the

threshold fairly high, so that only the biggest peaks of your signal cross the threshold and get squashed

flat, leaving the rest of your dynamics untouched. But just because a certain pedal has the word

"limiter" painted on it does not mean you can assume anything about its threshold setting- you still

must take care to adjust either the threshold or input level in order to match the threshold with your

specific signal peaks. Otherwise you may find that it does not work at all, or it squahes your signal too

much.

So "compression" in general is associated with a lower ratio, reducing but not killing the dynamic range

of the signal that crosses the threshold. Because of the lower ratio, you can get a much wider range of

effects by adjusting the threshold, even to the point where your entire signal is above the threshold. Of

course the results will depend on the specific signal and settings.

A lot of pedals have no ratio control, and a lot of them don't even state their ratio range (or fixed

setting) in the specs advertised by the manufacturer. So you may have to do some research to find out

whether a given pedal will work as a limiter. A lot of popular compressors for bass today are pre-set with

a very low ratio, and are not suited for limiting big peaks. And you can't make any assumptions just

based on whether the pedal has the word "compressor" or "limiter" painted on it. For example, the Boss

LMB-3 is marketed as a limiter, but it has a wide range of control over the ratio, so it can be used for any

sort of compression; whereas the Boss CS-3 is marketed as a compressor, but it has an extremely high

ratio, so it is really more of a limiter.

So the difference boils down to the pre-set or adjustable amount of the ratio, and whether you are able

to adjust the other parameters to achieve a specific compression goal.


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How to set up a compressor:

You want to know how to set the knobs on your compressor, or at least some good settings to start

with. OK. Here's a very simplified starting point:

If your compressor has just two knobs, typically labeled "comp" or "sustain", and "level" or "gain", then

just set both knobs at 12:00, their midpoint. Then adjust to taste. If the result is too noisy or extreme,

then turn the comp/sustain knob down to a much lower setting.

If your comp has more than two knobs, make sure all non-compression functions are turned off. That

includes expansion, gating, enhancing, and de-essing; and if there is a separate limiter function, turn it

off too. Read the manual if it is not clear how to turn these functions off--some knobs need to be turned

fully clockwise, but others need to be fully anticlockwise. Now looking at the compressor-specific

functions (such as attack, release, threshold, and ratio), set all of the knobs to 12:00. This will be a

reasonable starting place for most comps. Once you've got the compressor working normally, then you

can experiment with the other available functions. Always keep the limiter threshold higher than the

compressor threshold.

Of course you'll need to dial all of these controls in appropriately for your individual signal in order to

get good results--so the real truth is that you have to learn what each of the knobs does, and how each

of the functions reacts to your individual situation. All settings will be heavily dependent on the output

level of your instrument, the dynamic range of your playing style, and the results you want from the

compression.

Also be aware that every compressor works a bit differently from others, so you will have to learn the

individual features, quirks, and limitations of whatever comp you're working with. Even if you copy

specific ratio and attack settings etc., different units will not act identically due to the wide variance in

components and circuit design. The reason I do not give you more specific control knob settings to try is

that settings that work well for one person will not necessarily work for someone else.

Having taken all those factors into account, here is how to dig in deeper to set your controls correctly:

The very first and most important setting to consider is the level of the signal you're feeding into the

compressor. Some comps have controls for input level and/or threshold, but many (especially pedals) do

not. You need to have complete control over the point when your signal crosses the threshold, or else

you are just gambling and hoping that the compressor was designed in a way that just happens to match

your personal signal. Too often people buy a comp pedal and hate it because it squashed their signal too

much, or it didn't do anything appreciable, and then they say compression sucks. But 99% of the time

the problem was that their instrument signal level was not matched to the ideal operating range of the

compressor. When setting input level and threshold, remember that raising the input level is the same

as lowering the threshold. Also note that the threshold knob on some comps may be "backwards", so

that turning it clockwise lowers the threshold, increasing the amount the signal is compressed. If your


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comp has no input level or threshold controls, then you have to use the volume knob on your

instrument, or maybe another pedal that can boost or cut levels, in order to bring your signal into the

best operating range for the comp you're using.

The next parameter to consider is the ratio. Of course the usual thinking is that a low ratio (under 5:1) is

for gentle compression and a high ratio (above 10:1) is for peak limiting; but even those ideas are

dependent on the threshold and the results you want. For example a low ratio and a very low threshold

can result in a lot of extra sustain, while retaining fairly natural dynamics. A high ratio and a low

threshold results in a super-squashed signal. The ideal setting for peak limiting would be a very high

ratio and a high threshold, so that only the biggest signal peaks get touched at all, and they get capped

off completely. If you want to rein in a loud/boomy low string, choose a high ratio and then set the

threshold so that only those boomy notes cross the threshold and get squashed. It's all interactive with

your specific instrument signal, so you have to experiment and balance all these factors together. Some

comps have a fixed ratio; in that case, the only way to control the ratio is to select a comp that has the

ratio you need.

Attack and release are the trickiest settings, as they are completely dependent on personal taste and

playing style and expectations. A slow attack will allow more of your natural note attack though,

allowing for the greatest articulation and pick/pluck crispness; but it also allows more sharp peaks (from

aggro playing, boomy low notes, etc.) through at the beginning of each note, so you may need to

shorten the attack in order to catch those spikes. It's a balancing act. The release time not only affects

how each note sustains and trails off, but also affects the attack of the next note you play. If the release

time from one note crossing the threshold has not completely passed by the time you play the next

note, then the compressor will still be reducing your signal level overall when you hit that next note.

This can be useful if you want consistent smoothness and your playing is steady with no long rests;

inconsistent playing will result in inconsistent signal levels and weird peaks after a long rest. If you want

the comp to react only to each note, you have to choose a very short release time; but this can result in

a choppy or unnatural sound, with undesirable artifacts known as "pumping and breathing". So the

release time is the parameter that will require the most experimentation to get decent results. As with

the ratio, sometimes the only "control" over these parameters is to buy a pedal that is preset with

attack/release times that just happen to meet your needs. Also note that some comps will distort bass

signals if the attack or release times are too short.

Some comps will refer to "hard knee" or "soft knee". A hard knee means the comp will apply 100% of

the ratio you set immediatelywhen any of your signal crosses the threshold. A soft knee means a signal

that crosses the threshold by only a little bit will only be compressed by a low ratio; and the higher the

signal crosses past the threshold, the higher the ratio that will be applied. With a soft knee, the ratio

number you choose will be the maximum ratio applied to only the strongestsignals crossing the

threshold. A soft knee is generally considered to be a more "natural" sound, more like the response of a

tube amp for example, but a hard knee is often necessary for corrective compression like peak limiting.

The reason so many pedals only have two knobs, "compress" and "level", is because this keeps the cost


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down for both manufacturers and consumers. Fewer parts, simpler circuit, smaller box. Also it makes

the pedal seem easier to use. However, two-knob control is a problematic compromise because it

seriously limits your ability to dial the compressor in to work well for you. As with any circumstance with

a lot of compromises, you basically have to suck it up and live with those compromises, or change your

circumstances. If you are stuck using a two-knob compressor and you don't get the results you want, the

best thing you can do is adjust the level of the signal you feed it. That can really make a huge difference

in results, turning a cruddy noisemaker into a useful tool. If cutting or boosting your levels into the comp

still doesn't get you what you hoped, then your best bet may be to look for a different unit; at that point

you should be able to describe what exactly was not working for you (e.g. not enough peak limiting,

mushy note attack, etc.) and ask around for a comp that will work better for you.

Another thing to try: remove the compressor from your chain! Listen to your raw signal for a while and

maybe you'll find you didn't want compression after all, or maybe you'll find it helps you articulate

exactly what you were hoping the compressor would do for you. This will help others make useful

recommendations.

Good luck!


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What are Dynamics?

To an acoustic or classical musician the meaning is simple: dynamics are therange of how gently or strongly you play your instrument, from the quietest

possible sound to the loudest. But I recently saw a huffy dispute between two

electric guitarist/bassists about the meaning of this word as it relates toamplifiers, and I realized several interesting things. One, their views werenearly opposites, but they were both correct. Two, there is no standardized

and accepted language to describe the dynamic response of an amplifier.

Three, seeing all the pieces of this puzzle can help people understand moreabout why they like or dislike specific amplifiers. And four, the same

understanding could help clear up some problems people have with

compression.

The components inside any amplifier or processor have a set amount of

headroom, meaning there is a point where if your signal peaks reach a certain

level, the components will clip and deform the wave shapes of the signal. Inthe case of an amp or processor designed for ultra high fidelity, the idea is to

have the highest possible headroom. In the case of a distortion channel, the

idea is to have extremely low headroom, because you specifically want lots of

clipping. But clipping is not the whole story--the wave shapes get altered incountless different ways, and a "good sounding" distortion is one where the

specific deformation of the waves just happens to sound good to you.

Those are the extremes, but most amplifiers are somewhere in the middle,

neither super high fidelity nor heavily distorted all the time. Most amps and

preamps progressively alter the wave shapes in a wide range of response

depending on the strength of your signal and its dynamic peaks. When peopletalk about a preamp having "fat tone" or they say an amp is "very responsive

when you dig in", they are talking about these progressive alterations of the

amplitude and shape of your signal. All of these impressions of tonal responseare highly subjective, and we often don't know exactly what it is we're

hearing. We can only say what it sounds like to us using really vague terms

like "warm", "quick", "flabby", "tight", "modern", and so on.

Here's where it gets interesting! This is where the old story of the blind men

describing an elephant comes in, and why the two guys I saw bickering had

different stances on what makes an amp "dynamic". For one of them, an ampor DI with very high headroom is more dynamic, because the waves from

your instrument are conveyed transparently, without flattening the peaks

(compression) or other alterations. The other guy said that a transparent DI

sounded dull and lifeless to him, and he preferred hearing and feeling thedynamic tonal changes you get from a colorfully responsive amp. For him, an

amp that reacts more to your signalis more dynamic. These seemingly

opposite views are both right, of course, in that they are describing whathappens as you play softer or harder.


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To make matters more complicated, a person who likes an amplifier's tonal

response may think (or even believe with conviction) that it's because of theamp's high fidelity, though often the reality is the other way around. When

someone hears an amp or gain pedal that has a great "feel", but isn't adding

obvious distortion, they very often describe it as "transparent, doesn't color thesignal" yet at the same time "it just sounds better, warmer, phatter, morelively". No matter how great our ears are, and how experienced we are as

musicians or audio professionals, we often misattribute the reasons why we

hear what we think we hear.

This brings up the simultaneous blessing and curse of compression. On the

one hand, big fast-moving transient peaks in the low frequencies are the

source of our perception of depth and power, so an amp that doesn't hinderthose transients will have a hefty, strong sound with a broad dynamic range of

amplitude (actual level of the output). And overcompressing those transients

can make the lows sound gutless. On the other hand, the more "responsive"amp both adds and emphasises upper harmonic content in your tone, and this

inherently means some compression, even though it "sounds more dynamic".

At the more noticeable end of the range, this includes "grit", "grind",

"crunch", and other descriptions of light-to-strong clipping, which again is aform of compression with added harmonics. Those reactive changes, whether

clean or dirty, are what makes an amp sound or feel more responsive.

Another element is "sag", where the sound waves are altered by a drop in

voltage as your signal peaks demand more power than the amp's components

can deliver in that moment. Even without clipping, this is another type of

headroom interaction; the higher-fidelity amp/preamp will have a much higherreserve of power available so there will be no sag. Again, these seemingly

opposite behaviors can both be described as "dynamics".

Going back to your instrument, and the dynamics of your physical playing,

there too you'll find it's not as simple as it seems. When you change your

playing strength, you don't just change the volume of your signal, you alsochange the tone quite significantly. The amount your strings rattle on the frets

or whine against a fretless fingerboard; the quick pitch shift (twang) of strings

snapping back from a strong pluck; the sawing sound when you dig in with a

bow. All instruments and voices, even drums, change in tone across thedynamic range. I emphasize this point because a compressor should only turn

your volume up and down, and should not take anything away from those

tonal qualities!

In other words, when people say they don't like compression because they are

"a dynamic player", they fail to realize that what makes their dynamics worth

listening to is the tone and feel, not the amplitude. A sound that is too quietwill not be heard well, and a sound that is too loud will be unpleasant to hear,


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and neither of them will make your band sound good. Instead the ideal is for a

listener to be able to heareverything you have to say, from the softest whisper

to the angriest SMASH, and for them to enjoy hearing it, and for the wholespectrum to suit the mix with the rest of your band. You want to have every

nuance of your playing dynamics occupy a less extreme range of amplitude.

That is what compression is for: not killing your dynamics, but helping theaudience hear your dynamics even better!

Of course it's easier to get bad results than good ones. There is a steep

learning curve to using a compressor well, and frankly many compressors(especially the one-knob deals stuck in many amp heads) are just not very

good. A lot of them flat-out suck. So one option is to shop for a better comp,

and spend the time to learn its tricks. But many musicians don't have the

money for a really nice compressor, or they don't have the spare time to fusswith all the knob-twiddling and learning a piece of gear that they find

frustrating anyway. For them, the clear and popular choice is to buy an amp

that happens to enhance their dynamics by its inherent design and nature. Andthere's nothing wrong with that.

All that remains is to experiment and decide whether, for you, the

amp/preamp dynamics that suit you best are more like the power-hungry highfidelity of high headroom, or the interactive/responsive tones and soft clipping

of lower headroom. Both are valid interpretations of the word, and both are

musically useful means of transmitting the dynamics of your playing.


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Should you put your EQ before or after your compressor? Or both?

Both EQ (equalizers) and compressors are tools for controlling signal levels. EQ controls the relative

levels of specific frequencies; most often the levels set by the EQ are fixed at the one setting, not

dynamic. Compression controls levels dynamically, in response to your incoming signal level; most often

the levels set by a compressor are not specific to any particular frequencies- the increase or decrease in

level happens to the entire frequency range.

There are exceptions: there are a rare few dynamic EQ units, and there are a number of compressors

which can be set to affect only specific frequency ranges. Regardless of these exceptions though, it is

important to understand the general principle of how equalization and compression are different, and

how they can work together.

If you place the EQ first in the chain, then you can regulate the relative strength of different frequencies

in order to get a less obvious, more consistent and natural response across all notes. This can be

especially notable if you turn down the lowest lows a bit, since they have the strongest signal peaks. If

you want you can instead create a more dramatic squish in a certain range by adjusting the EQ to feed

higher spikes in that range into the comp. The downside of "EQ first" is that any later changes you make

to the EQ, changing tones between songs for example, will affect the response of the compressor.

If you place the compressor first in the chain, that allows you to make as many dramatic changes to the

EQ settings as you want, without having to adjust your compression settings too. The downside there is

just that you may sometimes wish for EQ to adjust the balance of your low end and high end levels into

the compressor.

So should you have two EQ's, both before andafter the comp? It's not actually recommended because

each stage can add noise and unwanted changes to your tone, and it all adds up. So sometimes the

added control over your signal is not worth the degradation of the signal quality. You have to balance

the benefits against the penalties with your specific gear.

To simplify and generalize, I'd say if you change your EQ settings a lot, you may benefit most from

putting the EQafterthe comp; whereas if you set your EQ once and forget it, then you could benefit

more from putting the EQ in front.


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Where to put a compressor in the fx chain:

It's almost entirely just a question of personal preference, but here are some considerations:

An envelope filter, or any other effect that relies on dynamic control from your instrument, will

usually go before the compressor since a compressed signal may not trigger the envelope

follower properly. Also, many filters put out volume spikes that can't be restrained just usinghand technique. On the other hand, some people want a more consistent, even response from

their filter; so in that case they may benefit from putting the compressor first. Both compression

and envelope effects are dependent on the levels of the signal feeding into them, so you have toanalyze your own case to see which way makes the most sense for you.

Overdrive, distortion, and fuzz compress your signal already, so additional compression is

often unnecessary. Additionally, compression can often roll off the "edge" of the distorted signal,

even to the point of nearly canceling out the dirt effect altogether (in extreme cases). So youdon'twant to place the compressor after the dirt. On the other hand, many overdrives work/sound

best if your signal has a wide dynamic range going into them, so in that case you wouldn't wantthe compressorbefore the dirt either! It's often best to just switch the compression off while

using OD/distortion. If that's not an option, just experiment to find the compromise that sounds

OK to you.

Most phasers, flangers, wah-wahs, vibratos, choruses, vocoders, and talkboxes are not too

particular about whether there is compression before or after; however some of them may put out

strong resonant peaks which could be kept in line by putting the compressor after.

Pitch-shifters often track better after a compressor, since the incoming signal is kept at a

steadier level.

Tremolo is an amplitude effect, where the whole point is a steep difference between the high

and low levels. So putting a compressor after tremolo is pretty much pointless. If your tremolo

needs a less extreme range, then turn down its "depth" knob.

With delay and reverb, if you put a comp after an echo effect the compression will increase the

presence of the trailing echoes, but on the other hand it will also increase any noise (for examplefrom an analog delay). If you use the noise gate feature built in to some compressors, though, it

will cut off the trailing ends of the echoes--so switch off the gate, or put it aheadof the echo

effect.

In the case of using a line-level rack compressor, your choices are fewer: it generally has to go

between your preamp and power amp, or in a line-level loop, which usually means it is going

afterall of your pedals. So you'll have to weigh the pros and cons of the effect of the

compression on yourwhole signalwith and without your other effects. Unless you just preferhaving the compression or limiting at the end of your signal chain anyway, I'd suggest that


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rackmount comps are better for people who don't change their tone around a whole lot, or where

your main use for compression is just peak limiting rather than sustain or a "squish effect".

"It killed my tone and my dynamics."

I see this line pretty often. There are several factors that can cause this experience:

First, it really is an unfortunate reality that many compressors roll off some of your high frequencies,

and our ears/minds hear that as a deadening of the tone. With units like that, the only easy solution for

brighter, livelier sound is to get a different compressor. The more challenging solution would be to

modify the unit you have with a better op-amp or wider-range input or output filtering, if you are

experienced in that sort of work. Don't bother adding an EQ or an enhancer/maximizer after the

compressor, as those devices cannot actually "put back" any frequencies that have been cut off.

Second, some compressors can alter your tone when you set them to heavier compression settings. If

you don't like the tone you hear from your comp, try using a lower ratio and a higher threshold. How

much that helps will vary widely depending on the specific unit you're using. Also, try lowering the level

of the signal going into the comp- that can help because some units use the input gain to determine the

threshold. I find that the majority of complaints about dead tone result from not understanding the

relationship between the output level of your instrument and the threshold (sensitivity) and ratio of thepedal.

Another aspect of the heavy-compression problem is that a large part of what we hear/feel as "huge

deep low end" is actually due to very tall amplitude spikes in the very low frequencies, because it takes

exponentially more energy to make a low frequency wave "sound loud" compared to a higher

frequency. If your speakers can take the resulting power spikes, then there's nothing wrong with rocking


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those huge wave peaks as much as you like. If you're at all concerned about blowing speakers, then

strong compression (limiting) is the tool you need to use, and losing the sound/feel of a pants-flapping

low end is a necessary sacrifice. But even if the speakers are not such a concern, you may like what a

"medium" amount of compression does for your tone in the highs and mids, but hate what it does to

your lows. That's why multi-band compression was invented; see my article about that. It's also

something that can be corrected by putting an EQ in the sidechain of the comp, to make the comp less

sensitive to low frequencies.

Most people who have had these problems with comps robbing the low end of its strength have never

spent time working with either the multi-band or sidechain systems. That's a normal situation, so my

point here is not to put those people down, but instead to let you know that not all comps behave the

same way, and there are better tools out there than the ones you may have used before.

As far as "killing the dynamics"... that is 100% a result of using too much compression. Compression is all

about modifying your dynamics, that's the point. But if it "kills them", for your purposes or tastes, then

you've got it set too strongly. Raise the threshold and lower the ratio. Or if your pedal just has two

knobs, dial back the one that controls the amount of compression. In the case of something like the Boss

CS-3, you'd dial back the "Sustain" knob, and also reduce the level of the signal going into the pedal in

order to raise the threshold. You may have to turn down the output volume on your bass to make that

happen.

Part of the problem is that people expect to hear the compression working, or hear some magic

improvement to their tone (extra "fatness" for example), so they turn it up until they can hear a big

change. But most of the time the correct setting of a compressor is found when you can'thear it

working. Extreme compression can be useful and cool-sounding in some specialized circumstances; but

the vast majority of the time you'd actually benefit most from a transparent "invisible hand" keeping

your levels under control without messing things up. And that requires lighter settings. If there will be

any tonal improvements from the compressor, expect them to be very subtle.

When people post that they hate compression because they are "very dynamic players", or because

they prefer to "really hear the difference between light playing and loud playing", I respond that if they

were using compression properly, the audience would actually hear their dynamicseven better, that in

fact compression is a tool not for killing dynamics (unless you want it to) but for making dynamics even

more articulate and audible. Here's how that works:

When playing with wide dynamics, there are two main things that "change sound" going from light

touch to heavy strike: the strings, and the clipping of the amp rig (for example tube/transistor

distortion/compression, speaker driver compression, and transformer sag).

The strings obviously vibrate differently as you play differently, and may rattle against the frets. They

will make all of their tone changes completely regardless of whether you have a compressor in line--

those changes are controlled entirely by your hands, and have no direct relationship to the level of the


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signal. You can change the volume without altering the tonal effect of dynamic playing of the strings.

The amp gets more or less distorted or compressed in normal operation, without necessarily having any

obvious overdrive effect or compressor feature. The amp will clip/sag based entirely on the level of the

signal. So for people who play tube amps loudly for example, a compressor really will have a negative

impacton the dynamic sound that player is accustomed to. But for people who play clean, expecting no

amp distortion, there's no impact. So my comment about making dynamics easier to hear is aimed at

clean-tone playing, not clipped-amp playing.

Given a clean amp, with all dynamic tonal changes coming from the strings, you then have your "quiet

tone" playing at a very low actual volume level, and your "aggro/strong tone" playing at a very loud

actual volume level. But you want the audience to hear both of those equally well! You don't want the

quiet stuff to be lost unheard, and from a practical standpoint you don't want the loud stuff to blow

your speakers. Compression, done properly, brings up the audible level of the quieter playing, making it

easier to hear subtle details, without taking away the "feel" and tone of softer plucking. And by reducing

the height of the stronger signal peaks, you get the freedom of really digging in to the strings for an even

more dramatic dynamic string tone, without as much concern about damaging your cones, and without

"making" the soundman turn you down in the PA mix.

In other words dynamic playing is as much about tone as it is about volume, and getting the most out of

your dynamic playing can mean maximizing the amount of tonal change your audience actually hears

and appreciates--and that can mean reducing the changes from maximum to minimum volume, with

compression.

What to do if your compressor seems to kill the "energetic tone" of your

dynamic peaks


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This question was sent to me recently, and even though I sort of answer it

with other acticles here, I felt this one specific situation deserved to be

highlighted:

"I've found that when I go from a heavy hand to a light hand it is a really

effective tool to draw out the nuances of the light hand. My style is tonormally play with a reasonably light touch ...and then when I want to get amore extreme sound, I dig in. Having a compression level set low enough that

it effects my standard playing seems to kill my 'extra' that I give. I've yet to

ind that balance where I can hear the difference without feeling squashed."

There are actually a myriad of possible answers/approaches to this. One thing

to listen for, and experiment with, is the actual soundof the "extra" that you

give. For one example, theoretically if the only thing that really changes is thelevel of the signal, with no clipping anywhere, then that "extra" effectively

has no distinguishing sound. It's just louder. If that is (or is close to) the case,

and you find that the extra burst of loudness is really what you miss, then thebest solution is to get an amp with more headroom, and speakers that can

handle higher wattage. That way you have greater dynamic range with no

clipping, and a greater ability to use the louder peaks cleanly and without fear

of speaker harm, with little or no compression needed.

If you want the compression benefit of increased articulation of your lighter

playing, without the penalty of excessively squashing your heavier playing,then unfortunately you are battling against the physical realities of most of the

devices available to us--it's a very tall order. Your best bet is a comp with a

very low ratio (2:1 or 3:1) and a low threshold. This is where a pedal like the

Diamond BCP-1 really shines. It allows you to spread the benefits aroundyour whole dynamic range, yet it is not capable of squashing. Another option

would be to combine any comp with a product by Toadworks called the

"Enveloope". What it does is blend your clean signal with your effected(compressed) signal, in dynamic response to the levels of your playing. In

"reverse" mode, it would blend in more compression when you play more

lightly, and reduce the amount of compressed signal when you dig in. Atleast, it should--I haven't actually tested that idea.

If you use an amp that overdrives nicely, and gives you a gritty or crunchy

breakup whenever you hit those big peaks, and if you want that sound; thenyou'd probably benefit from either turning up the output gain of your

compressor so that your overall signal is closer to that breaking-up point at all

times, or you'd want to use a line-level peak limiter after the preamp section

of the amp. A lot of amp heads have such a thing built in, but those usuallydon't sound very good. Or you might be in one of those cases where you really

don't benefit from compression at all. That's completely legitimate.

Another (very common and likely) scenario is if the biggest tone change from


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that "extra" digging in is actually from the strings themselves, or the fret buzz

and general clatter of a moment of heavy playing--in other words all in the

bass itself, rather than the amp. A lot of that zing, grind, clatter, and buzz is inthe upper frequency range--so if the comp you use happens to attenuate the

highs when compressing heavily, then yep, it "kills" that extra tone. This is

very common, especially from dbx rack units and cheap pedals. There arethree main solutions:--Use a comp that doesn't attenuate the highs so much, under heavy

compression.

--Use a dual-band comp, so the highs aren't necessarily attenuated at all whenyou hit a big slap or pop or pluck with a lot of low-frequency energy;

--Use a comp that naturally enhances the high frequencies. Some of my

reviews mention a particularly "zingy" or "bright" or "cutting" tone, and those

would probably suit you.

Another angle is to use a setting that I use more often than not: a high ratio

with a very high threshold, and a very fast release time. That's a peak limiter,and if you dial it carefully, your signal is not affected at all until you hit peaks

that you do not want to pass. A "better quality" pedal or rack capable of this

setting should be able to do it without much noticeable tone loss. If there is

still some amount of amp overdriving you want to achieve, you just set themake-up gain so the limited peaks still get up into the drive range you need.

Remember that many comp pedals have a relatively low ratio, so you only getpeak limiting or an audible "effect" from them if you crank the "sustain" or

"comp" knob up high. In those cases, that usually results in yourwhole signal

being squashed badly. Since so many comps tend to roll off highs when

compressing heavily, and since it is squashing your whole signal all the timein this case, the net result is that your tone sounds dull, dark, lifeless, or

crappy. To avoid this, you must take care to observe the threshold and ratio of

the compression; observe the tone "behavior" of the comp when it's workingheavily; and try to keep your signal from being overwhelmed and abused.

When all else fails, you may just have to try a different compressor--one that

doesn't kill tone.


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How does a compressor increase sustain?

With a typical comp, there are two components: one that provides gainreduction, and one that provides "make-up gain". The gain reduction element

is what drops the level of your signal as it crosses the threshold. Since the

peaks are reduced, and since what out ears/brains actually hearis the averagelevels (averaged between the quietest and loudest moments), that means whenthe peaks are reduced, the average is reduced too, and the signal sounds

quieter to us. So the second element, "make-up gain", is a simple clean boost

of the overall signal level to bring the average levels back up to the level theywere at before compression.

So now the average levels are back to normal, but the dynamic range has been

reduced, so the net result is that the noise floor (and the "floor" of lower-levelsignal from your instrument) has gotten louder. Anything that was previously

quieter, has now been turned up by the amount of make-up gain you applied.

For instance, as your notes trail off, they naturally get quieter; but now thattrailing-off happens at a much shallower slope than before, because it has less

distance to go, from high to low level. So your notes last longer--more sustain.

It's just because you are turning up the volume of the whole signal, while

turning down the level of the peaks.

The higher the ratio =

the more the peaks are compressed (reduced in output level) =the narrower the dynamic range (from loudest to quietest sound) =

the shallower the slope as your note trails away =

the more your note stays "near" its peak level while decaying (increased

sustain).The lower the threshold, the more of your signal gets compressed--again

reducing the dynamic range, etc.

What makes one comp better than another for increasing sustain is a

combination of those two elements, plus (ideally) having low noise. Since the

noise floor of your signal is usually increased to about the same degree thatyou increase the sustain, any extra noise from the comp becomes especially

noticeable. There are a few comps that minimize this problem by skillful and

crafty engineering; and there are a few that manage to increase the noise

much more than you'd expect, or where they actually introduce their ownoperating noise. Bear these extreme cases in mind, when trying out any

sustainer.


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UNCH!

People use the word "punchy" to mean different things, so often there isconfusion when somebody says a particular pedal or sound is "punchy" and

the next person doesn't hear it that way. For some people, it is a sharp clear

attack at the leading edge of each note; for others it is the "hump" ofamplitude peak that comes a few milliseconds afterthe leading edge. So forexample, comparing the EBS MultiComp with the Demeter Compulator, each

of them will sound "more punchy" or "less punchy" compared to the other,

depending on the expectations of the person listening. Either way though,compressors in general improve punchiness by increasing the amount of time

the signal stays near its peak amplitude. That way there is a greater perception

of "loudness" at or near the beginning of each note, without raising the overall

level of the signal, which helps your sound punch through the mix withoutoverwhelming the other instruments.

You can achieve a more punchy sound with your comp by carefully listeningto the way your signal is being compressed, and using whatever controls and

indicators are available to adjust the response so that the first moment of each

note, maybe around 200 to 400 mS, is being compressed and held at a steady

level for that short time. Ideally you would use a high ratio (maybe 8:1 or so)and a hard knee, and a slow attack may also help depending on your playing

style. I find that it helps to visualize the wave shape of the signal: try to

picture a line showing the envelope of each note rising and falling, and adjustthat line in your mind as you adjust the controls of the compressor, trying to

match what you see with what you hear. Ideally you will achieve a signal that

has a high plateau at the beginning, then drops off sharply, and then trails

away with a smooth slope.


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Is it true that compressors are noisy? Can the noise be avoided?

All compressors, even the really expensive ones, have the potential to add noise. Most of themwilladd

a bit of noise in normal applications. The reason is that compression reduces the peaks of your signal,

which also brings down the average signal level. Our brains focus on the average levels, not the peaks,

so reducing the peaks makes the whole signal seem quieter. To make up for that, nearly every

compressor has a boost stage at the end, called "make up gain" (sometimes just labeled "level"). This

gain stage boosts the level of the entire signal, including any noise that may have been in the signal path

already from your pickups, preamp, pedals, room wiring, or a variety of other sources. You may not have

noticed the noise before, but it was there- and the gain stage on the compressor just turned up the

volume on it.

Additionally, anyactive signal processor may create a bit of its own noise, depending on how well it was

designed and the quality of the parts used. So with compressors you get a combination of those two

noise sources: noise that was already there in the signal, now amplified; and noise created by the actual

circuit design and components of the compressor. That second noise source is where you can see

improvement between a crummy cheap compressor and one of better quality. That's one factor in my

reviews when I say a compressor has "low noise" or "more noise than I'd like". Good comps and bad

ones will both amplify existing noise, but good ones are well-designed and made using high-quality

components, and ideally should not add much noise of their own.

Now, to complicate matters a bit, there are many different types of compression circuit, and some types

may be inherently more prone to amplifying noise. But it's hard to predict the results when shopping for

a specific type of processor, as again it will vary depending on the way that particular model was built.

Sometimes a comp may be designed to boost the high frequencies, which will result in more noise

heard. Sometimes a pedal circuit will be sensitive to grounding issues anywhere else in the instrument-

pedal-amp chain, resulting in hiss that's hard to solve. Some comps are designed with such low

thresholds and high ratios that they can't help but boost noise a lot under normal use, even if the circuit

itself is supposedly not noisy.

Another issue that I've run into many times is that some designs are very prone to picking up ambient

electro-magnetic noise in the room. Tube compressors in particular give me endless problems this way.

You may have a compressor that I say is "too noisy", but you don't hear any noise at all, and it's partly

because you're in a different room, a different building and neighborhood, with different electro-

magnetic fields.

Most often though, noise from any kind of signal processor is caused by ground loops or other


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grounding (earthing) problems. There is no universal standard for the way circuits/devices are designed

in terms of grounding, which means that some devices which work great on their own, or with certain

other gear, will work terribly in connection to gear which was just designed a bit differently. The

ground/common of any one device is connected to grounds of all the other devices in the rig via several

possible routes: the shield of the patch cords, the negative wire of non-isolated power lines, or metal

rack rails for example.

Is there any way to combat the noise? Well, you can turn down the highs on your rig. You can eliminate

other noise sources in your signal chain, such as overdrive pedals or any sort of extra

amplification/gain/EQ/boost stages. You can put any noisy items afterthe compressor instead of in front

of it. You can check for ground loops in your rig- they can be hard to track down, but ground loops are a

major source of noise that most people do not even realize is going on in their system. Here is a very

good article on that subject:Rane Note 110.

As a last resort, you can use a noise suppressor or a noise gate- but honestly I would strongly

recommend doing what you can to reduce the sources of noise before adding any gear that will alter

your signal even more. Seethis article for more about noise gates. Many people consider buying a

rackmount compressor because certain models contain a noise gate as a feature, but this is a bad idea--

the gate is a very poor solution to most noise problems.

Did somebody tell you that a compressor would help reduce noise in your rig? They were wrong! :-)

Is a compressor necessary? ("Another guy told me he never uses compression.")

Short answer: No, it's not for everyone. A compressor is a very useful tool, and just as with any other

tool, the better you understand how to use it the more useful it can be. There are a lot of circumstancesin which a compressor is the right tool for the job. But that doesn't mean you have to use one. Many

people prefer to regulate their signal peaks as much as they can strictly through playing technique. And

many amplifiers (especially tube amps) compress your instrument signal a little or a lot just by the

nature of the amp design.Read herefor more about that. Overdrive and other types of distortion also

compress your signal considerably. So under many circumstances it may not be "necessary" to use an

external compressor. It's up to you to analyze your particular situation and determine if a compressor,
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as a tool, can be useful to you. Remember too that misusing a compressor will get you bad results,

exactly the same as misusing any other sort of tool. If you apply a chainsaw when you needed a fine

dovetail saw, it'll be bad news for your woodworking project. But don't blame the chainsaw!

So why would somebody want to use a compressor? What is it good for, and when? Here are the basic

benefits, which vary from one comp to another:

-Peak limiting, to avoid blowing your speakers or hearing unwanted distortion.

-Evening out levels between strings or between soft and strong playing.

-Changing the attack and other envelope qualities of your notes, making them squishier, rubberier,

crisper, or other amplitude effects which may be difficult to achieve just with your fingers.

-Emulating some of the tone and envelope qualities associated with older recordings (Motown, early

rock and funk, etc.) in which tube and transformer-based recording equipment and reel-to-reel tape

recorders got "saturated" by the bass signal. That saturation compressed the recorded tracks.

-Increasing sustain orpunchby increasing the average level of the signal without increasing the peaks.

This can provide greater perceived loudness, fatter tone, more audible harmonics, and better placement

in the mix.

Also, even though some people say they don't like compression because they play with a wide range of

dynamics, the fact is that carefully applied compression will actually make the entire dynamic range

easier to hear, rather than making your signal sound "less dynamic". This is partially about the quality of

the compressor, partly about the type of compressor it is, and partly about how the compressor is being

used. Failing to adjust the level of the signal going into the compressor can make anyone hate

compression. And some compressors just suck.

Some amount of dynamic control can be achieved just using your fingers, and that is a really important

goal to work towards while practicing. However some signal spikes can't be prevented with your hands,

such as a resonant peak from an envelope filter, or a flanger or delay set to high resonance. And some

players like to rock out with wild abandon, which means they need a limiter to keep their signal in check,

to avoidunwanted speaker distortion.

As far as the various tone and envelope changes for flavor or fatness, they are completely subjective.

Either you want those changes or you don't, and that's fine either way. Sometimes that rubbery thump,

or boosted harmonics, are exactly what the song needed! And one compressor may be good for getting

the tone/envelope changes you like, while another seems to do nothing but deaden your sound and add

noise. That's normal. Read my article about good settings, and if that doesn't help then try a different

compressor. But don't assume that because you have good dynamic control with your hands, or because

you tried a pedal in 1985 that sucked, that compression is no good for anyone. It's a very useful and

powerful (yet subtle) tool, but you must pick the right tool for the job and learn how to use it properly. I

don't think compression is for everyone all the time, but I do think a professional musician should have

the ability to use a compressor well, as part of their tool box of skills.
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Dual-band or multi-band compression:

The basic idea is that your instrument signal gets split into two or more frequency ranges using a

crossover. So for example it gets divided into lows and highs, with little overlap between them. Then

each "band" runs through separate, independent compressor circuits. Then the compressed signals get

recombined back into one mono signal of full frequency range. The benefit is that strong signal peaks in

one range, passing the threshold and triggering the compression, will not cause the otherfrequency

range to also be compressed. It is common with regular single-band compressors for the highs to be

"swallowed" (attenuated too much) when a low note triggers the compression, as the compressor will

reduce the signal levels ofeverything at that moment.

So if you play quickly up and down the fretboard or keyboard, or if you mix strong aggressive playing on

a low string with more nuanced playing on the higher strings, then a multi-band compressor will allow

greater articulation, clearer tone, and more even signal levels across the full range of the instrument.

However there are "cons" as well: there may be audible artifacts if the crossover component is not well-

designed. The lows of a bass will often seem cut back, less deep or powerful, due to the greater relative

presence of the highs and mids. And some compressor users just prefer the sonic effect of the

traditional single-band comps.

In general I recommend multi-band compression for tappers, slappers who want a bright sound, people

who play a lot of harmonics and ghost notes, extended-range instrumentalists, and others who find

compression takes too much away from the detail of their sound while playing across a wide frequency

range. For most other players -especially ones who prefer smooth squish, deep boom, or a more "glued

together" sound quality- I recommend traditional single-band compression.

Here are the dual/multi-band comps I can think of at the moment:

Rane DC24

EBS MultiComp

Trace Elliot SMX

FEA Dual Band

Digitech Bass Squeeze

TC Electronic C300, Nova Dynamics, and Triple C

BSS DPR-901II

Ashdown Bass Comp

Aphex Dominator 720

Rocksonics MB-3X

Many other rack comps have a feature that allows you to leave the low frequencies uncompressed, via a

sidechain, and this can offer results somewhat like dual-band compression... as long as you wanted less

compressed lows. A common example is the dbx 166A/XL "Contour" button. The Focusrite Compounder

has a similar feature with its "Huge" button, mixing uncompressed lows in with the compressed full-


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range signal. Again, several other manufacturers make units with this type of function--you just have to

figure out the "hidden meaning" of whatever cryptic name they gave that button or knob.

Parallel (blended) compression:

You'll see some compressors with a "blend" knob, or read about certain recording engineers using

parallel compression, and perhaps you'll wonder "what's the point?" since mixing the compressed signal

with the original uncompressed signal essentially undoes some of the effect of the compressor. Fair

question!

The idea is that sometimes you may want the thickening or increased sustain that can be gotten with

compression, but you may not like the way it flattens your dynamic peaks. Sometimes those peaks are

what gives your sound its "feel", its sense of depth, power, or vitality. So blending can be a good

compromise. This can be done subtly, or as a huge and interesting effect, depending on your

compressor settings.

One method is to use the "aux loop" on a mixer, which is typically mixed in parallel with your dry signal.

Or you can use a second mixer channel input instead of the aux loop return, giving the compressed

signal its own EQ etc. alongside the dry channel. Another approach is if you have an amp or pedal with a

parallel effects loop. Such a loop may be fixed at a 50/50 blend, or it may have a blend percentage knob.

Unfortunately you can't assume that every effects loop runs in parallel, if you don't see a blend knob, so

read the manual. In either case, mixer loop or amp loop, be sure to choose a compressor that will

operate correctly at the signal level your specific device's loop was designed for, instrument level or line

level.

The other method is to use a comp that has a blend built in. There are increasing numbers of those,

especially in pedal form. Some, like the Barber Tone Press or Guyatone ST2, blend the whole frequency

range; while others, like the Seymour Duncan Double Back, have the option of blending in only part of

the dry frequency range, like highs or mids. Some rack comps, like the Focusrite Compounder, blend in

some uncompressed lows in order to make the bottom end sound bigger.

Be aware that whenever you mix a signal with a processed copy of itself, the two waves will interact

with each other, and their differences in phase or polarity can sometimes result in a thin sound with

weak lows. Any time you add processing to a signal, its phase will be altered or its polarity may be

flipped 180 degrees; but this only matters IF the blended result doesn't sound good. If that happens, you

can try a different compressor, or add a device that has a phase switch/knob such as the Xotic X-Blender

or the Radial Phazer. With a comp that has blend built in, the circuit designer will generally have

addressed any phase problems already, so you don't have to worry about it.


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Low frequency notes tend to have bigger amplitude spikes, so the trick is to let them be big enough to

sound full and strong, while controlling them enough that they don't cause clipping in your amp or

mixer. Compression is all about compromise, and blending is all about compromise; so the bottom line

about blended compression is you have to experiment with it and find the right balance of

compromises, to find out whether it suits your tastes and does what you want.

What is an expander, a gate, or a noise suppressor? What should you do about noise?

An expander and a gate are two versions of one type of processor--basically the opposite of a

compressor. Their sensors respond to incoming signal levels just like a compressor does, but they affect

the levels in the reverse manner, increasing the dynamic range of your signal rather than decreasing it.

The controls, and the meaning/function of those controls, are otherwise the same as the ones on a

compressor. The threshold controls when your signal will trigger the effect, and the ratio controls how

much the signal is increased upon crossing the threshold.

Typically an expander is used to improve the signal-to-noise ratio of a recording, but it can also be used

for special dynamic effects like making a bass line more percussive, or helping vocals pop out in the mix.

A gate is a type of expander; the difference is that when your signal level reaches the threshold, a gate

goes from "closed" (no signal passes through) to "open" (all of your signal passes through). It's all or

nothing, on/off. Some gates offer more advanced control such as ratio or attack/decay, but basic ones

are just open or closed. This is a common way of controlling noise and hum from high-gain distortions,

single-coil pickups, and other noisy circumstances; when you pluck your note, the gate opens, and when

the note dies down the gate closes, keeping quiet until the next note. Of course this means that while

you are playing, any noise you had will still be there, at full volume. I don't recommend this unless you

are making intentionally choppy-sounding music.

A noise suppressor will either be a gate or a filter that cuts out the high frequency range where noise is

usually found (up near 20 KHz)--or sometimes both a gate anda filter. In either case, they work by

removing part of your signal, cutting out highs or cutting off the beginning and end of your notes. A few

of them do this cutting with less brutality, more elegance, but there is no getting around the fact that

they will remove more of your signal than just the noise. Because of this I do not recommend ANY noise

suppressor, at any price, unless you have no other option.

Many guitarists will find that with a high-gain amp setup and high-gain pedals there is just no way to

prevent getting a wash of noise and feedback; so for them a noise gate may be a necessary and normal

part of working with that big distortion sound onstage.

For anyone else who isn'tcascading high-gain stages, there is usually a better way to reduce or eliminate

noise. Try shielding the cavities of your instrument, or making sure it is grounded properly. Identify


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inherently noisy pedals, and replace them with non-noisy ones. Try using isolated power supplies for

your pedals.Search for ground loops. Check out your gain staging to be sure you have each stage set as

clean as possible, often by setting the input gain low and the output level high. This is because input

level (gain) is usually an active boost and will add or amplify noise; while output ("master") volume is

typically a passive cut from the maximum internal gain, and does not add extra noise. One way or

another, it is almost always better to solve the source of noise problems rather than spending money on

anotherpiece of equipment just to do a mediocre job of hiding the noise!

About tube (valve) compressors:

For people seeking fat, warm, "vintage" tones, the idea of a tube compressor is very compelling. Afterall, tubes and compressors on their own are each advertised as making everything sound fat and warm,

so the two of them together must be amazing; and The Beatles and most other famous bands of that era

were recorded with tube compression, so let's go buy a tube compressor, right?

Unfortunately, it's not so easy. There are several issues:

Most so-called tube comps on the market are really just a solid-state optical comp followed by a tube

make-up gain stage. So really they are the same as using any optical comp fed into any single-tube

preamp. This can sometimes sound good or even fantastic, but let's not mistake what we are actually

getting. Nearly always, in modern products, the tube has nothing to do with the compression part of thedevice. So if you have an optical comp andeither a hybrid amp or a tube gain pedal, you've already got

the same thing as what's typically sold as a "tube compressor".

The legendary studio devices used in vintage recordings had a lot more going on inside them than that:

multiple stages of different kinds of tubes, not just a single 12AU7; and audio transformers and opto

cells that had their own tone and action that is hard to replicate using off-the-shelf components. A single

preamp tube can never sound entirely like a more complex all-tube circuit with input and output

transformers. Again it may sound great, depending on the particular device and your personal tastes,

but one tube is only a small part of the overall tone picture of a vintage recording. You may even be

better off using a digital or solid state tone shaper that emulates more of the sound qualities of the

whole device or system, rather than relying on just a single component like a preamp tube.

With tubes, voltage and current make a big difference in how the device will sound. Electronic

designers have to carefully choose how the tube will be powered in their circuit, to optimize its

performance; but all too often the Accounting Department makes them choose the powering system

that is cheapest, not the one that will sound best. Cheaper usually means lower voltage, lower current,

and DC instead of AC. It is possible to make a tube device that sounds good with low voltage DC power,

but that is an extra design effort that many manufacturers do not bother with. They seem to reckon that
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if the tube produces gain at all, that's good enough.

Realistically, there are many tube-containing devices out there where the tube does nothing good to

your sound. They can make your tone mushy and indistinct, or they may do nothing audible at all. Again

this is about marketing and accounting: they want to sell you the idea of "fat, vintage warmth" without

actually providing anything but a weak, poorly-executed gain stage. NOTE: This is in no way a criticism of

alltube devices, just a warning about some of them, especially at the lower price points.

Many tube devices are vulnerable to picking up ambient noise from household wiring, nearby power

transformers, flourescent lights, ground loops, and so on. Noise problems like this can be a real pain to

try to solve. That's the one thing that keeps me from using a tube comp very often--I can't stand hiss,

and I get frustrated by trying to hunt for mysterious noise sources. I've gotten multiple emails from

people saying their tube comp is not noisy; I suspect instead it was their electro-magnetic environment

which was not noisy. Sometimes it's even due to a differently-designed grounding system inside your

amp or another processor, something that cannot be easily changed. The tube comps that I have

reviewed positively happen to be ones that showed some resistance to outside noise.

So what's the answer? Honestly, all you can do is use your ears, and don't believe the hype. Don't

believe the advertising text about fat vintage tone, and don't fool yourself into thinking any device that

has the right specs/features "on paper" will actually sound the way you hope. Try before you buy, or buy

from a place that has a good returns policy, whenever possible.

All that said, there are some great-sounding tube comps out there. My favorites are the Effectrode PC-

2A, Retrospec Squeezebox, CAE V-Comp, and Markbass Compressore, they're amazing. The ART Levelar

is not too bad for its low price. And note that with a rackmounttube comp you are more likely to get a

properly-designed circuit with appropriate power, compared to most pedals. I just haven't covered the

rack units so much because they tend to be large or expensive--I will try to provide more reviews and

information on those in the future.

What are the differences between various types of compressor?

Compressors are often described with category names like VCA, optical, FET, feed-forward, OTA, and so

forth. These names are for different circuit designs, for the part that actually follows and reacts to your

signal level, and the way in which it reacts. Naturally you will wonder "how do they sound", and why

would you pick one type over the others.

The first thing I should say is that it's like the difference between lime green, grass green, Kelly green,

forest green, etc. They are all different enough that you would have reason to pick one over another if

you're painting a room, but you can't make a useful comparison without actually seeing them next to

each other, in context; and whether they are "very different" or "very similar" just depends on your

perspective. Also bear in mind that while comps certainly can affect your tone, the type of compression

circuit doesn't actually tell you anything about the tonal effect.


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VCA stands for Voltage Controlled Amplifier. Technically most comp circuits could be described as VCA's

in a sense, but in practical usage it means an IC chip that contains transistors that follow your incoming

signal level (voltage) to determine how much gain to apply. VCA's are typically associated with fast,

clean compression with precise controls over attack and release. Symetrix, dbx, Boss CS-3, Maxon

CP9Pro+, and Alesis 3630 are examples of VCA comps. Most cheaper rack comps are VCA controlled. The

THAT Corporation, originally a division of dbx, produces most of the VCA chips you'll encounter.

FET stands for Field Effect Transistor, and FET comps are essentially a subset of VCA's, with their own

particular qualities. FETs are often used as a solid-state emulation of tubes, but the main reason a comp

will be advertised as FET-based is so you'll associate it with the famous and coveted UREI 1176. So it's

mostly about the marketing, but you can expect more "color" in the effect than from a clean VCA. Aside

from the 1176, the other examples of FET comps are mostly expensive rack units by brands like Vintech,

Daking, Purple, and Chandler. The MXR M87 pedal is supposedly a FET comp, but it sounds just like any

regular VCA unit.

OTA stands for Operational Transconductance Amplifier, which is a chip like a VCA except its output is

variable current, not voltage. In this context it refers to a specific circuit design based around the

CA3080 chip, which is the basis for the Ross, Dynacomp, Keeley, Wampler, and probably 90% of all comp

pedals on the market. Most "boutique" comps, with all their claims about refinements and

developments for ultimate tone, are just versions of this one very simple circuit--sometimes with no

improvements other than a fancy paint job and a 3PDT footswitch. Its envelope is a bit hard to describe,

but it happens to work really well for guitars.

Optical comps contain a light source that gets brighter as your signal gets louder, and a light-sensitive

resistor that reacts to the brightness of the light by increasing its resistance, to cut the level of your

signal. In some older designs these were separate components, but in 99% of modern designs the light

and the resistor are encased in one small black cylinder. Optos are generally described as very smooth,

slow, and "organic". They can be very neutral/invisible, or very squashy/effecty, depending on how the

circuit is designed. Optical examples include Demeter, Diamond, EHX Black Finger, Retrospec, and

Joemeek. ELOP is just a trademark of the brand Manley, for their opto comp design.

Tube compressors, almost always, are really optical comps with a simple 12AX7 tube gain stage added

on the end. However vari-mu (short for Variable Mu, also a Manley trademark) designs use a vacuum

tube in place of a transistor, where the variable voltage input changes a tube's bias instead of a

transistor's gain. It has a somewhat different action, generally described as very smooth or even

"creamy". Aside from the Manley and some very old Fairchild units, the only other vari-mu-style

example I know of is the Markbass Compressore.

Feed-forward means the control circuit will receive ("hear") your signal before the signal goes through

the amplifier stage; this is the more modern approach. Feed-back means the controller receives the

signal afterthe amplifier stage, and this is more associated with older designs. "How they sound" is a


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very subtle shade of distinction, you'd have to try both to have a feel for it. Most of the previously-

named circuit designs can be built to feed forward or back.

There are lots of other circuits for compression that don't necessarily fall into a named category. The

Orange Squeezer is its own thing, based around the JRC4558 chip, with a unique action. The TLC (Trans

Linear Conductance) circuit by Aguilar is its own thing, similar to a VCA but not one exactly. Advanced

electronic designers like Rupert Neve develop circuits that are either completely original, or they use

pieces of earlier designs but in a new way that doesn't have a name yet. So not every comp fits a neat

category.

Pressed for a short and easy simplification, you'd probably be OK generalizing that VCA comps are fast

and modern and precise, while optical comps are slow and vintagey and organic. But remember there

are plenty of exceptions to those descriptions. And all the rest of the "types" have their own subtle

differences in action that are really hard to put into words--you would just have to compare them in

person, to get a feel for it. So this still doesn't tell you how they sound, but at least now you have an idea

what it all means.

What is a sidechain? How is it used for ducking, noise suppression, or bass emphasis?

Normally a compressor or other dynamic effect will react directly to the audio signal you feed it, the

same signal that will then be compressed or processed. A side chain is an extra input that allows thedynamic processor to react to a different signal, allowing a wider range of possible effects on the audio

signal at the output. Some sidechains have an external in/output jack, while others may only be

connected to an internal parallel signal path.

I've been struggling to come up with a decent analogy to help explain sidechains, and so far the best I've

come up with is a "fake ID". Imagine a youth who wants to buy alcohol, but the local laws prohibit sales


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to people under a certain age. So the kid acquires a fake ID card that says he is of the legal age to buy

booze. So for the purpose of the liquor store transaction, he is an adult; but when he drinks the liquor,

he is still a youth. Now let's imagine the ID card says he is actually Itzhak Perlman or even Aretha

Franklin, and this gets him or her into the VIP rooms of a fancy concert hall. He's treated like musical

royalty, but he's really still the same youth, and he experiences all these different treatments as his

original self, not as the person he's pretending to be.

The most common way to use a sidechain is to take a Y split from the input signal and process it with an

external device like an EQ. Then the EQ'd signal returns to the sidechain input of the dynamic processor,

which then performs its effect on the original non-EQ'd signal. Again, the signal at the output has not

been touched by the EQ, but the compressor/processor did its dynamic reaction to a copyof the signal

that was run through the EQ.

For example with a bass signal, the waves of the bass notes have much bigger signal peaks than the

higher-pitched tones do, so those peaks trigger the dynamic response of a compressor much sooner

than the rest of the signal would have, which may result in overcompression. This can be heard as

muddiness, dull tone, or a loss of low end. If you use an EQ in the sidechain to turn down the lows a bit,

then the peaks that hit the dynamic detector will be more even, the low-frequency peaks won't be

higher than the midrange, so the compression will be more consistent, and you can set it accordingly. If

you turn the lows in the sidechain down all the way, the end result can even work and sound like a bass

expansion.

As a switchable feature this system is included in a few comps like the Focusrite Compounder, dbx

166A/XL, ADK CLA1, and FEA Opti-FET. Their sidechain is hard-wired internally to an EQ which (in most

cases other than the FEA) is preset for the lows at a fixed frequency. With these units there is no need to

use an external processor or an in/output jack; these are examples of internal parallel signal paths.

Many rack compressors feature a sidechain jack for use with an external processor. This processor

doesn't have to be an EQ, it can be any sort of effect or gain control or whatever else. For example you

could send your audio signal to a tremolo effect via the sidechain output of a compressor, and then that

tremolo-pulsing signal would return to trigger the compression. The results may or may not be musically

desirable, or worth the trouble, but it's good to know you have that kind of option available.

Another technique is to feed the sidechain a completely independent control signal, like a miked drum,

or a click track, or another instrument in the band. This allows you to have a great deal of creative

control over how the processing will affect your audio signal. It's very popular in techno music to apply a

heavy-squashing compressor to a bass track, and trigger it with a drum track. The same thing can be

done with filters, gates, or any other sort of dynamic processing; and the control signal doesn't have to

be rhythmic, it can be random. Some studio engineers will "fix" the timing of a musician who has poor

rhythm by gating that musician's mixer channel, and triggering the gate from the channel of someone

else in the band who has good rhythm. It's also fun to apply an envelope filter effect to vocals or sax for

example, and trigger the filter with any other channel of the band mix. Get creative!


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Using an external trigger or processor means using a sidechain in/output jack on the dynamic device,

typically a 1/4" TRS with the plug format "tip=sendring=return". In other words there is only one jack for

both the send and the return, which means you need a special cable in order to do this. For sending your

signal off to external processing and then returning, you need an "insert cable": a Y-shaped cable with a

TRS (stereo) plug that splits off to two TS (mono) plugs. If you are using a completely outside trigger-

signal source (like a rhythm track), then you'll take a balanced (XLR-TRS or TRS-TRS) cable and make sure

that the signal output at the source device connects with the "ring" (return) connector of the sidechain

jack. This may mean rewiring a plug at one end of the cable, swapping its tip and ring wires.

One practical application used in broacast and PA systems is "ducking", where you have two audio

channels and the volume of one is controlled by the volume of the other. A common example of this is

the voice-over:

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