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Sound System Processing Equipment

Updated on April 15, 2010

Mark Bilger - Sound System Operator and Designer

The Author While Desperately Looking for a Better Pix
The Author While Desperately Looking for a Better Pix

Welcome To SoundAdvice - Sound Processing Equipment

My name is Mark Bilger and I've been involved with sound system design, sales, operation, training, and installation since 1972. I've been around in the sound world so long that some of the first systems I mixed for nightclub bands were a pair of 5-foot tall "columns" with (4) 12" speakers in each cabinet. The amplifier/mixer "heads" had just 6-channels and were severely overtaxed because of lack of speaker power and the whole band trying to sound like professionals who played in arena venues.

Today we have plastic speaker cabinets that can actually be carried two-at-a-time by a reasonably sturdy man and they can handle a whole band for small to medium nightclub gigs. Peavey recently introduced a new Impulse 12D speaker with a lightweight neodymnium-magnet 12" speaker and a ribbon transducer for high frequencies that has a 600 watt RMS - 1200 watt peak power amp built in! They weight just 39 pounds each and I've heard them at a music trade show. They just kill. We have 7 pound amplifiers putting out 1600 watts RMS (I've got one myself and it's awesome) and 13 pound power amps putting out 6,000 watts RMS with total reliability.

One could literally surround an arena stage with flying banks of 80 of these self-powered plastic cabinets (48,000 watts RMS) and sit 60 lightweight Peavey self-powered dual-18" subwoofer (60,000 watts RMS) cabinets on the floor today for about $140,000. The combination would likely perform better than the complex systems Michael Jackson and Mr. Mister toured the world with back in the 1980s that cost upwards of $1,000,000.

We're going to give you some basics of sound system processing equipment in this hub - compressor/limiters and graphic equalizers. I always try to provide my articles in plain English without using technical terms so they're understandable to everyone from beginner to intermediate user. Advanced users might get bored but might learn a thing or two anyway. So everyone is welcome to visit and find out how much is available to learn.

This hub will mature with time so check back. Happy hubbing!

Compressor-Limiter Front Panel

A Behringer Rack-mounted Compressor-Limiter
A Behringer Rack-mounted Compressor-Limiter


Some sound people avoid compressors like the plague because they don't understand what it does. Others have a compressor limiter in their rack but it just sits there doing mostly nothing or is by-passed. I’ve got a simple explanation that I’ve used when asked about compressor-limiters while selling equipment in a retail store. It goes like this:

A compressor makes loud stuff quieter and quiet stuff louder so it becomes mostly the same volume and the material is literally thrown out of the speakers at the audience. The limiter part of the unit is like a brick wall so that if the sound gets up to that volume, it can’t possibly go any farther.”

That sounds like an over simplification, and you're right, but it’s also essentially true. Not technically accurate but true. If the audio signal exceeds the level (threshold) you’ve told the compressor to start working at, the signal gets mashed into submission. If a signal is lower than the level (threshold) you’ve set, nothing happens. So you can turn up the signal going into the compressor until the incoming signal is considerably larger - meaning everything quiet becomes louder - but the compressor still kicks in and mashes all loud peaks that exceed the level (threshold) you set earlier. All the stuff below the threshold is now louder but the stuff exceeding the threshold is automatically mashed into being quieter - just like my express description given above.

The typical full-range compressor, connected as the last processor (master compressor-limiter) before going into the signal snake to the crossover and/or power amps up at the stage area, affects all sounds equally. If strong bass dominates the mix temporarily the whole mix gets mashed by compression caused by the strong bass. If a strong snare drum smack dominates the signal, the whole mix gets mashed by compression caused by the snare drum. Any signal that exceeds the threshold, whether it’s a single instrument or voice, or a group of instruments or voices, causes the whole mix to get squeezed. This can be a problem if your mix sucks so you must be careful...

But... A "Master" Compressor Can Make Life Easier When You Understand Them

My goal is usually to have most of the instrumental music SUB-dominant to (less than) the vocal mix by a little bit but not enough to lose the music’s powerful presentation. In contrast to the way I've heard many amateur sound people mix (especially in churches) musical instruments should always be riding right along just barely below the vocals. You can envision this humorously as the heads of vocalists sticking up out of a turbulent ocean, barely bobbing around above the water singing at the top of their lungs while the ocean water attempts to drown them. You, as the sound person, can use the compressor-limiter to have control of an air pump that puts more or less air in the singers' life jackets that keep their heads above the surface.

Having the vocal mix exceed the compressor's threshold by a small amount more than the instruments do, which will mash the instrumental mix and fatten it up, means the instruments are also automatically pushed slightly out of the way while the vocal or vocal mix is dominating. This is an excellent effect for live performance because it automatically keeps your vocal heads above water without much manual effort on your part. The compressor acts like a very fast (a few milliseconds!) set of precision hands "virtually" pulling soundboard instrument channels down slightly while boosting the lead vocal or mixed vocal channels slightly. If I get my mixes and compressor settings just right, a master compressor can almost run the mix for me while I relax and listen to tonality of individual channels without worrying about whether the audience can hear the words over the music. The effect should NOT be noticeable to the audience though and should be very subtle.

You may be saying, “But what about instruments that take a lead solo?” You’ll love this… When singers have stopped singing for an instrumental lead solo they are no longer dominating the mix. The instruments automatically come back up slightly to fill the void cause by the absence of singers and keep the system's output level about the same. Now you can move just one slider to bring the lead instrument up just a little out of the compressed blend of instruments and it dominates the rest of the instruments like the vocals did before and the remaining instruments fall back a tiny bit. Not enough that the audience notices, but enough for the lead instrument to be heard prominently. You need to be careful so the lead vocal or lead instrument doesn't become too awfully dominant and cause the mix of everything else to get buried or lose its powerful presentation.

Besides using a compressor-limiter as a master unit, you can also use them on single channels or submixes of channels. Let's say you want to compress the group's vocal mix but not the instruments. If the vocal channels can all be assigned to Submix 1, the submix of the soundboard likely has an insert jack. If so, the compressor can be inserted there with an insert cable. In that application, the vocals are mashed into submission to avoid loud yells and whispers that are lost - before the final blend of all the submixes.

In another use of compression, a compressor-limiter could be inserted (insert jack again) in the bass guitar channel and set to compress at an 8 to 1 ratio. That makes thumped low notes and popped higher notes closer to the same volume when you adjust the threshold correctly. Bass guitar is no longer lost in the band but fattened up so much it's more "in your face" and strong.

I never recommend using a compressor on individual vocal channels though because the insert jack is before the aux sends. That means the singer's vocal monitor signal will be compressed. Unfortunately a singer will blow their voice out trying to increase their dynamic volume while the automatic compression holds their volume down.

The one exception to not using compression on a vocal monitor system is if singers are using earbud monitors and all earbud monitor mixes MUST have a compressor-limiter on it to save the eardrums of the listeners from destruction. This is a FACT and not a theory.

Graphic EQ Front Panel

One channel of a 31-band 1/3-octave equalizer
One channel of a 31-band 1/3-octave equalizer

Graphic Equalizer

A salesman or advertisement told you that your sound system speakers are “flat” – but they’re not. "Flat response" typically means that all frequencies of the audio spectrum are reproduced equally, no matter how high or how low the sound is. Even expensive studio monitors can't be completely and perfectly “flat.” If they were you wouldn’t prefer the sound of one over another. They’d all be exactly the same and you could use any brand and get the same result. There would only need to be one brand of studio monitors because there would be no difference.

You may have been told that it’s cheaper to not buy, and easier to not learn to use, a graphic equalizer (EQ) because your sound system is pretty “flat” and doesn’t need it. If you believe that, I've got some oceanfront property in Oklahoma that I'd like to sell you. Even if the system seemed flat while located in the store where they had acoustic tile ceilings and carpeted floors, it certainly won't be that smooth when you take it other places.

You definitely should have a graphic EQ for your main or Front Of House (FOH) system that the audience hears - at the very least. Personally, I'd never try to run a monitor system for the stage performers without a graphic EQ but people continually try it anyway. Everybody on stage suffers just to save about $100 for a monitor graphic EQ and one hour of learning how to use it. You’ve been told that you can control the tonality of your live mixes using the EQ knobs of the soundboard channels and save the money you would spend on EQs. That's simply bullsh*t to the max. People who say this stuff drive me wacky.

The main problem is that your live performance sound system for the audience, even with the very best, most expensive, speaker components and finest electronics has to perform in a wide variety of acoustic situations - from a concrete block gymnasium with a metal roof and hardwood floor that bounces every sound from every hard surface - making the sound unintelligible, to a nice small carpeted room with thick acoustic tile ceilings where the sound is similar to someone’s living room. I’ve performed as a bass player, and run sound for bands, in large hard surface rooms where a 500-watt sound system with no subwoofers could be deemed excessive, yet I’ve done smaller, deep-pile carpeted nightclubs where we could have pumped out 4000 watts and it would have been just right because we were pumping about 3/4 of our available 2500 watts at the time and it wasn't offensive. Much of this disparity concerning power requirements, seemingly in reverse of a musician’s logic, is because of the acoustic reflectiveness (bounciness) or (in reverse) the absorption coefficient (ability to absorb) of the room, number of people in the room, and other items that absorb or reflect in that room.

If you’re thinking of using a graphic EQ in a studio situation, the theory behind its operation is exactly the same. You are attempting to match two speaker systems to the room they’re in. You can install all the baffles, rubber padding, egg crates, blankets, etc. that you want and the studio monitors are not going to be acceptably flattened until you add an EQ to fine tune the speakers' output sound to the specific environment. The studio monitor speakers might be perfectly flat in a testing laboratory chamber somewhere but when you put them in the real world of a home or pro studio, they must be forced electronically to conform to the new environment. That can only be accomplished with a graphic EQ (or parametric if by analyzing the room you find that there are only a very few problems) and a sound analyzer capable of using digital electronic ears to “listen” to the room like no human ears can possibly hear. It tells you exactly what to change to “re-flatten” your monitor speaker outputs to match that specific room.

If you don’t "equalize" the system, whether in a studio or at a live performance venue, you have no reference point to start from when mixing. You would essentially be mixing blindly in a thick fog while not knowing where you are compared to the real world. If you DO "equalize" the system your mixing begins at a very similar starting point every time. There needs to be a “master” standard that lets your sound system do its very best (in live performance venues the system still may not sound as good as it can because of quirky problems of the room but at least you have overcome the worst sound problems of the room and can have a successful gig instead of a total disaster) in every performance environment.

That “master” standard is your overall system graphic equalizer (EQ) precisely set to overcome the most obvious defects of the room you are in. The graphic EQ is inserted into your system equipment after the soundboard and before the power amps. Its settings are altered to fit each room that your system performs in. This is also true of your performer stage monitor system(s).

In some countries the phrase “feedback speakers” is sometimes used to describe the speaker enclosures that performers hear on stage (the sound is "fed back" to the performers) but I detest using that description because in the U.S. the word “feedback” is considered to be a squealing, howling, ringing horrible thing to eliminate. I’ll be using the word “stage or floor monitors” throughout this publication.

Anyway… stage monitor systems are always adversely affected in some way or another by room acoustics and will never be the same from room to room - no matter how good or expensive they are or how flat the manufacturer says they are. The only exception is earbud monitors, which are not affected by room acoustics because they’re shoved right down in your head. Thus every stage monitor speaker system must have a graphic EQ before the signal gets to the power amp if you expect them to sound good for the performers at a reasonably high level of volume.

Flipping back to the main (FOH) sound system... Of course there are many factors involved in getting a decent (or as close to studio quality) main system sound for your listeners. But the very first and most crucial factor is to create a standard, a reference point, a master system basis from which you work your magic on the mix of instruments and vocals. That is accomplished with a “master” graphic EQ used to match the system to the room. Only then can you hear accurately to shape the mix. The goal is to cause the system to operate the same in every environment it is taken to so that your soundboard mix remains very close to the same for every performance.

Whether you are a single act playing under a thatch roof in the tropics for tourists, a 10-piece horn group playing in a concert hall converted from an old movie theater for 1,000 people, or a concert arena group slamming heavy metal at 40,000 head bangers, you must have a master graphic EQ as one of your final equipment components to match your sound system to the inferiorities (deficiencies) of the venue. You must have graphic EQs on every stage monitor mix to alter your performers’ reference speakers to overcome the acoustic deficiencies of the stage they’re performing on.


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    • electronician profile image

      Dean Walsh 

      5 years ago from Birmingham, England

      Thanks for the thorough answer Marc, great example.

    • MarcoMarks profile imageAUTHOR


      5 years ago from Fort Myers, Florida

      Hi electronician,

      A compressor-limiter is just a compressor that has a limiter added to it.

      A compressor "mashes" the signal so loud stuff becomes softer and soft stuff becomes louder, thus reducing the dynamic range of material. It affects the sound so you don't want to use it on classic music but it's excellent for contemporary music. Actually virtually all rock music is recorded with compression, many times on the individual tracks as they are being recorded, and always on the final mix as it's being mastered. There are "multi-band" compressors as well, with a different compressor compressing bass, low mids, high mids, and highs so that a large kick drum punch that triggers compression doesn't affect the drum cymbals, for example, that happen at the same time. But the large drum cymbal crash that needs to be compressed also doesn't affect the snare or kick drum when that happens.

      The limiter has one job - make sure NO signal exceeds the point it is set at. This is crucial in digital recording because digital distortion is ugly and sounds awful. So you set the limiter to zero db and the level can never go up into digital distortion no matter what.

      The compressor-limiter can be used, for example, on a feed going from a church sanctuary to the baby nursery. When it's set correctly the nursery operators can dial up one volume on the TV, listen to the music undistorted until the sermon starts because the compressor mashes it to fit the TV speaker's capability, the limiter assures the level never exceeds the TV speakers capability, and then when the loud music is over, the compressor releases and the volume of the sermon preaching comes up to the same level the music was. Thus the whole program is very controlled and the nursery operator doesn't have to keep twisting the TV knob to turn music down and turn the sermon up.

      It's also used on the main sound system in any venue. Compression helps keep an excellent mix so that the vocalist doesn't get lost beneath the music, the cymbals don't get lost under the keyboard player, the snare drum doesn't take everybody's heads off, and every instrument is delicately balanced to give a radio or CD quality mix (assuming it was mixed pretty well before the compressor-limiter, it will sound even better after it). Meanwhile the limiter makes sure the vocalist's mic that gets dropped on the floor doesn't blow out a horn driver or subwoofer speaker, the hip-hop tracks don't take out subwoofers because they like severely heavy bottom, and a kick drum of a rock drummers set doesn't punch the power amp hard enough to make it distort and blow subwoofer speakers. The limiter says, "Hey... this is as far as you're going at that volume and you're not getting past me no matter what you do!"

      Compressors and limiters or compressor-limiters are used in TV, radio, recording, live performance, and I've even used them in home entertainment systems. They're available worldwide so this is not a U.S. invention unknown in other parts of the world. My favorite for the kind of material I'm typically involved in is Behringer, designed in Germany and built in China but there are far more expensive ones as well.

      Hope that helps answer your question.

    • electronician profile image

      Dean Walsh 

      5 years ago from Birmingham, England

      Interesting - never heard of a compressor-limiter. I am wondering, are there any domestic uses for these or are they only ever used for stage performances?

    • MarcoMarks profile imageAUTHOR


      6 years ago from Fort Myers, Florida

      Thanks to both of you for your kind comments. I hope what I have written helps you out.

    • profile image

      FASHANU Richard 

      6 years ago

      Thanks alot Sir, actually you've made my day. Your writeup is actually well informed. I have been looking for this type of advise and instructions, I run a small sound engineering set-up here in Nigeria, and I have been looking for better and experienced hands to mentor me in the business, most of the sound engineering we have here do not impress me in the output production they offer their clients and that is what forced me into the business to offer better services. I will be grateful IF you will accept to mentor me properly in this business. My email is

      Thnks so much sir.

      Richard, from Nigeria, West Africa.

    • profile image


      7 years ago

      Hi Mark,

      I would like to greatly appreciate your sharing your great incite and experience in sound mixing with us. I have gained a whole lot out of your article.



      Kampala, Uganda


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