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Compressor Threshold

ian hatch

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Hi All

I know the subject of compressors has been covered many times before, but this is a slightly different question.

I know the basics of how compressors work IE: ratio, gain, threshold etc. but how do you work out where to set your threshold level?

From a novices point of view, the way I see it is:

You sound check, so your average PFL is reading "0" on the meters, and anything above that needs compressing.

So why don't you just set the compressor's threshold to"0" and compress every thing above that?


Just a quick second question, do you sound check with compressors on or bi passed?

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You sound check without any compressors, and then add them in if they are needed, during the soundcheck.


setting the threshold to 0 with a 1:1 ratio will still give you signals above 0db the ratio and threshold work together, you work out how to set your threshold level with experience and practise within the industry, knowing where you want the sound in the mix.

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do you sound check with compressors on or bi passed?


I would always start without compression then add it where required.


You may, for instance, find that a particular singer tends to sing at a general level except on certain notes when they suddenly let rip. This can be infuriating to mix, so letting the compressor deal with it will really help. You'd set your threshold so that none of the acceptable singing was compressed, but the loud bits get cut down to a level you can cope with. This would be a matter of just compressing the one channel.


Otherwise, you may be mixing a musical and find the whole band tend to get overexcited in one song, doing some bits at a perfect level and others just too loud to get the vocals over. You may want to get a compressor in there and put just a touch of compression on so it's not obvious but makes life easier for you. Again you'd set the threshold above the OK level and below the difficult level. This time you'd be compressing a group rather than a channel.


It's less usual to compress the whole mix if working with live sound. You might need to compress the whole mix if you were making a recording, to even out the dynamic range so listening at home is more comfortable. Again, you'd be trying to set it so it's not too obvious but working in the background unnoticed.


why don't you just set the compressor's threshold to"0" and compress every thing above that?

Finally we come to limiting. This is where you set the compressor so the sound can not go above a certain level. This means setting a threshold at, say 0dB, then setting the ratio to full. When this kicks in you will hear it. The band will be playing louder but the sound level will not get louder. It's a bit wierd, to be honest. It's main use is in recording - especially broadcast who use it a lot - to ensure the signal cannot distort due to over-high levels. It has virtually no place in live music or theatre.


As Rob says, you get used to setting compressors with practice and experience. It's not just where to set the threshold, or what ratio to use, it's a matter of working the two things together.


Personally, I usually look at the meters to see how much compression is happening and when. My ears tell me what it sounds like and the meters tell me what's happening technically. After a bit of practice you start altering the settings without really thinking about what you're doing, but just knowing it'll work. Have fun gaining the experience! :)

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Well, I have a policy of always putting vocals through comps, so they are in from the getgo.


If I'm starting cold with an unknown vocalist, I use a higher threshold and gentler slope than 'normal', then as the vocalist annoys me I adjust to suit, but the compression is always on, even if it's just doing a bit of excess enthusiasm curbing. It usually ends up somewhere around three or four to one, and the compression light just coming on most of the time he's singing. Just gives a chunk of solidity to the vocal performance in terms of mix placement. Enthusiasm curbing means I can run the vocal a bit higher in the mix than without compression, and thats how I like it.

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Whilst I agree with Rob and JSB, it must be added that compression is a little subjective, as can be seen so far we all have our own ways of using the technique.


In this instance, practise makes perfect ( or thereabouts :) )


As far as the sound check settings, comps, gates, limiters are usually off on the vocals, then Superman comes in and adjusts the settings, as soon as the vocalist opens their mouth :) At light speed of course.


Other instruments vary greatly, as to the technique used.

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Compressors are, I think, an area where you really have to grasp the theory and terminology before using. It's very easy to get things in a real mess!


One of the best primers I've found on the topic is on the "Rane Notes" pages, with the compressor section being HERE.



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My 2p worth


I find a little compression on a few unstable/unreliable muso's helps keep things tight and balanced, years ago when I had 2 boxes on sticks I used to compress the whole mix to squeeze more volume out, but these days thats not a problem.

generally this is what I process


1) vocals :Desser, and gate poss some compression/limiting depending on style (loud screaming rock anyone?)

2) bass gtr : tiny bit of tube compressor just to tighten the bottom end and add some warmth

3) kick drum: limiter/ gate

4) brass: light compression just to keep things under control and not take out peoples ears

5) snare : again some limiting/gating depending on style


obviously this changes, but as a guide........


incedently just tried out some alto ACL4 guad compressors, fantastic, found them more musical than the behringers, ok there more money but not loads more, and they look awsome very BSS looking anyhow, get yourself a compressor to play with, run CDs through it, find out different effects you can create, I always say a little is better than too much, sometimes a little compression here and there is better than over compressing the whole mix or indeed one source.


happy squeezing!:)



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Out of interest, if you get hold of the Alan Parsons Soundcheck CD so beloved of sound engineers everywhere, you'll find lots of tracks of individual instruments (and drums :) ) which are recorded without compression. You can run these through a desk and try compressing them. It's a great way to practice without anyone else present!
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