hi forgive my ignorance,but can someone give me a clear and concise answer to my question please and maybe an example of when / how to use.

compressors / limiters???????????
what are they and what do they actually do.
do they protect your rig from a blowout?
or maybe tighten up the sound somehow.

i have it in my head a compressor squashes the sound tighter sort of

or am i way off the mark.

no khz or sine wave stuff as i dont understand all that science lol.

cheers

To put it simply, it is like an automatic volume control.

When the input signal to the amps gets to a certain level, the compressor/limiter can cut in to prevent the level from causing clipping thus protecting the speakers from receiving a distorted clipped signal.

Below the "cut in" level, it doesn't affect the signal.

cheers tony, sorta thought that.
would i also be right in thinking my active berry's have it built in? or is it recommended i obtain a limiter?
i always assumed that a pair of actives would automatically not be able to exceed their own capabilities, but after reading some of the posts here i got to wondering if they are protected properly at all.

what got me thinking was, i was gigging last week at a largie oblong room fairly empty with no columns or walls or drop bulkheads. about 120 or so people.

now i know clipping occurs but what does it sound like?

on a few tracks i heard a sort of echo?????? or maybe a replay of a solid sound.??????????

weird description eh.

no lights were on on the cabs and i wasnt driving particularly hard.

when i thought about it i assumed it was the hard sound bouncing back from the back wall a split second later, or maybe it was clipping????????????

cabs are fine, not stopped working or anything.

Hi as I understand it a compressor is a clip compressor which you set the perasmiters for clipping.Clipping is a cut off warning point just before your signal goes square wave and distorts.Distortion is what blows speakers and this helps to put a barrier thee if u like.


Now then a limiter...im sure someone will correct me if in wrong im a bit scetchy on these.
As I undersand it a limiter is for cutting off db and frequencies that are over a certain levil.

You can limit the db parramiters and and lets give a hyperthetical situation....a karaoke singer screams n whoops down the mike..as soon as they hit the deired db it cuts out the sound to protect amp from clipping.

Ok hope this helps And im sure someone will scold me iff ive led you in the wrong direction.

Ps i have a 1 u limiter compressor and gate (oh dont ask me about gates lol) sat around brand new...i never used it lol too complicated,I just have my hand ready on the slider.


Paul

No that was the sound being reflected back.. Mild cliping is hard to hear with the human ear.. Thats why we have lights etc to show us this. Heavy cliping is distortion as in a distorted guitar sound.

Dont know what model of speaker you have but I have some small Db Basic's that have a built in sort of limiter that holds the signal short of cliping.

Also your gain structure should be set correctly to avaid cliping any where from player to mixer mixer to EQ and EQ to amp. Once clipping or distortion is introduced to a signal it can not be removed.

I know you did not want tech talk but a sine wave is like the letter S put on its side and then repeated like a snake over and over again, if you were to flatten the top and bottom of the S this is what a clipped signal looks like.

Now if you imagine your speaker moves as we travel down the snake it moves out then returns down the snake to the centre then the speaker moves in ie down the snake to the bottom and then repeats this over and over again.

If you clip the signal via an amp then the speaker shoots out and cant travel any more then shoots in and cant travel any more and if done over and over may damage the speaker.

a compressor softens out any spikes or peaks in a signal at a threshold set by the operator (you) and as said above only comes into play at a set level. You can have what is know as a soft knee compression this is where the compression is added slowley as the signal gets louder so giving less of a pumping sound.

A limiter is like a brick wall the sound will hit the wall and will not be aloud to go any higher.

Compressors and limiters are great when used correctly but can make your sound, sound very bad if used incorrectly.

Less is more, a well set up compressor should not be noticable to the punters.

Hope this helps and I have kept it basic enough lol

Nik

Just had a look at the spec for the Behringher B215A and it does say that it has some form of protection. It says that there is an "optical" limiter but I don't know what they mean by that. You are a bit safer using actives because the amps are matched to the speakers so there is less danger of over driving but you could still have the input level too high.

What protection the optical limiter gives I don't know.

optical limiter eh? i reckon that means the little red led lol. if its red its clipping and you can see it rofl.


thanks for the info guys, i dont reckon i need a limiter / compressor just yet then but if i find one cheap enough i'll have a punt and buy it and have an experiment with it.

good point nik about making sound awful if not set right. took me ages to set the parameters on my lexicon unit for a decent warm vocal sound then i ruined it all with a berry mixer with fx lol. doesnt sound as good as the fx on the lexicon.

I've not known of an optical limiter in a professional device before, but have seen them in home studio/domestic speakers. Optical limters bypass alot of the voltage monitoring millarky (bet I spelt that wrong), by having a small festoon type light bulb inside (like the bulbs used in in-car interior lights above the car doors etc, which are fitted to the crossover inside a speaker cab. The bulbs are in-line with the signal on its way to the speaker driver, and glow to constantly variable amounts as the music changes - most of the time it just looks like a little sound-to-light Maplin/Argos party light. The optical monitoring is simply a light sensitive photoelectric cell, pointing at the festoon bulb... If/when the bulb gets "too bright" the photoelectric cell turns down/off the signal to the driver, or that section of the crossover.

The benefits of light creation and monitoring is mainly the isolation factor - no heat, current, or voltage overloading is transfered across the gap between bulb and light sensor. Of course...when the bulbs blows...


Anyway...Compressor/Limiters... there's a DJU Review on one of the more popular and "cost effective" makes/models. Which can be found here, on DJU

Glad to be of help lol.. The Lexicon make fantastic FX units where as Bheringer make ok ones.. You will not get the same quality and warmth on the Berry as you will on the Lexy lol.

Nik

that has decided me, i will get one. i read the berry manual and panicked lol. i got a virtualizer pro and was just staggered at the all the functions. sold it after 2 weeks lol.

Great bit of kit when set right.. I read some reviews before I got one and some people said they were rubbish. But if used correctly they are so much better than a normal compressor.

Nik

Most amps are designed to be driven by 0db. Around a volt in amplitude.
Most CD players put out 0db.
So as long as you dont go above 0db on your mixer you should be OK.

My MP3 player is a bit on the low side but I can go by the cd player as to what is the right level.

Most DJ grade amps and many active speakers have optical limiters..they're the easiest and (perhaps more importantly for the designers) the cheapest form of limiter. They are used in studios sometimes for that 'vintage' sound as well. Gary describes it well, the filament bulb (or sometimes an infra-red diode with capacitor) models the 'heat' in your speakers and reduces gain by picking up the emission by a detector diode and feeding it into the VCA circuit. The idea is they protect your speaker voicecoils from cooking..however most of them are fixed at the max amp level and only act as clip limiting..not output limiting. Therefore a large enough amp with smaller speakers can still overdrive them.


Compressor-limiters for DJ or stage use should not be confused with musical compressors for vocal recording (though they are based on similar principles). A musical compressor (eg the Urei / Drawmer / Joemeek etc) are mic-channel units which even out the vocal level during a recording to allow good reproduction of both quiet and loud vocals without booming or being drowned out. They can also be used live but tend to cause a PA to go into feedback if you're not careful as they effectively turn the mic up during periods of no singing etc.

A peak limiter is essentially a compressor with immediate attack and long release, stopping output signals going over a certain level (threshold) no matter how large they become at the input by reducing the gain proportionally to the amount the input exceeds the threshold. Below the threshold the gain stays at unity (becomes passive). You can set the gain to over-react and reduce the gain by more than required, but this causes a drop in output and volume everytime the threshold is exceeded and defeats the object of a 'transparent' limiter in a venue.

A good example of a musical compressor in use is Eric Prydz 'call on me' where the bass seems to make the music 'pump'. This is the compressor set 'incorrectly'...in his case for musical effect (I hope!).

The Formula Sound AVC2 that is beloved (?) of resident DJs in pub installations around the country is an example of a limiter with >1 gain reduction, when you exceed the limit, the sound actually goes down below where it was before you hit the threshold. It's saved many an expensive PA installation!