Tools for Mixing: Compression

22 06 2010

A while back I got the rare opportunity to work with the youth band of our church.  These guys have an incredible heart and passion to worship and have loads of raw talent which translates into a powerful time of worship.  When they lead, as a worshipper I feel free and emboldened to praise God the way He created me too.  When they lead, as a sound man I have to work as hard and quick as ever to create a decent mix to help facilitate that worship.

As is the case with most youth bands and even many churches, they are not using state of the art or high dollar gear for their services.  Now don’t get me wrong, they are not operating with the bare minimum.  The system includes an Allen and Heath console, JBL speakers and subs, and solid system processing.  What I longed for that night was individual compressors.  Maybe this never happens to you, but in a mix including 3 vocals, an un-caged drum set, two electrics, acoustic, bass, and keyboard, I had a hard time keeping the vocals out on top to lead the group in worship while keeping the music strong.  The vocals that I had that night are gifted in leading worship, but for a variety of reasons (key of the song, dynamic range, mic etiquette, etc) their volumes were all over the place and the second I took my finger off their faders I would either lose them or have way too much of them.  With 7 wedges, acoustic drums, 3 amps and a very small stage, I was dreaming for a few compressors to help me layer the mix the way I wanted.

For those of you who aren’t familiar with or maybe don’t know how to use one of the sound man’s most useful tools, the clearest definition of compression that I’ve ever seen is this: “Compression is the art of making louder parts of a composition appear softer, and conversely, the softer parts appear louder.”  That night, if I would have left the lead singer’s fader in one spot for the entire night his volume alone would have ranged anywhere from 85 dB to 120 dB.  Alright that might be an exaggeration but he got loud.  When he was closer to the 85-95 dB volume he could barely be heard over the drums and guitars.  Neither end of the spectrum is really acceptable in a good mix, so compression comes along and makes it possible to narrow down that volume range to make things more mixable.  Let’s say I have a 20 dB range between a vocalist’s quiet singing versus their loudest singing.  With a compressor I can take that 20 dB range and make it as small as a 1 dB range, but since I don’t want to eliminate the artistic dynamic range that the singer is using to create the mood or feel of what they are singing, I can get that range down to a very manageable 5-8 dB that will make mixing significantly less complicated but still leave some of that dynamic in place.  So how do we get our compressor to do that?  With some understanding of the compressor’s settings you can be on your way to a smoother sound and a less stressful time behind the board.

Threshold

In simple terms the threshold is the point where the compressor starts to do its thing.  Since there is a wide range of compressor and mixer brands I’m going to talk about these settings more generically as opposed to using the numbers on the knob.  If the input meter on your console (let’s say negative infinity to +15 dB) matches that of your compressor, things will be a little clearer as the numbers will match.  You must first set the gain (or trim) of your channel on your mixer (on my regular console that is around +3, or typically where the green lights first turn to yellow or maybe the yellow light just starts to glow on the meter).  Now if your numbers match, and your vocal meter is showing signal between -5 and +10 dB, I’d start with my threshold set close to 0 to +5 dB.  If your numbers don’t match, once your gain is set turn your threshold knob and find the area where the gain reduction lights just come on.  Begin with your threshold there and if you find it’s not compressing early enough you can lower the threshold from there to make it kick in sooner.

Ratio

This one is a relatively simple concept.  The ratio simply says for every x dB the source goes up in volume, the compressor will only let the output go up y dB.  For example, if you set a vocal mic with a 3:1 ratio, for every 3 dB the vocal increases coming into the board, the output will only increase 1 dB.  You can think of the ratio as setting the size potential of the source.  If you want it to be able to go bigger, you can leave your ratio smaller.  If you want it to stay a little smaller, or perhaps be more under control, you can set your ratio higher.  I tend to start with a ratio of 3:1 for most vocals and guitars, and often times I will go 4:1 or even 5:1 on drums or very dynamic guitars.  My preference is to start low and if you need more compression (less range) you can always increase the ratio.  The reason it is my preference is simply this, I don’t want to take away any more control from the musicians than is absolutely necessary to make the mix work well.  If I start it at 5:1 when 3:1 will do and don’t adjust it down, I may be holding that source back.  If I start low and it’s still too big, I can easily adjust my ratio up.

Attack

The attack is how quickly the compressor responds to the volume change.  A slower attack will sound a little smoother, rounding out the sound of your source a little bit and in essence making it sound a little “fatter”.  A slower attack will generally be less noticeable which can be good for vocals and some thin or scratchy guitars.  Setting your attack to a faster setting can be great for instruments such as drums or any other very aggressive instruments.  A faster attack will give an instrument more of an aggressive, pumping feel, and potentially bring out more of the high end edginess.  The ultimate decider on where to set this is by listening.  I tend to set vocals a little slower, guitars in the middle, and drums faster to start.  From there, if you need a little more aggressiveness or snap you can speed up the attack, and if it needs to be a little smoother or fuller you can slow it down.  As in all things with sound, let what you hear guide your settings and adjust until you are happy.

Release

The release is the back side of the attack, and sets how quickly you want to release the compression once that loud burst is over.  As with the attack, a slower release will sound smoother and less noticeable but could end up taking some of the aggressiveness out of aggressive instruments by compressing them when they don’t need to be.  I again will tend to start a little slower for vocals, middle of the road for guitars, and faster for drums.  You’ll want to again experiment with where to set this by listening to the sound.  If the source sounds like it is pumping a little bit, slow the release down to help even it out a bit.  If it feels like you might be losing something on the next note/beat, you likely need to speed the release up a bit.  Again, let the sound of the source guide you to where it should be set.  Listen and adjust until it sounds right to you.

Output

Most compressors have an output to help boost the volume of the end result, and here’s where I tend to see a lot of mistakes made.  Now that you’ve taken that 85 to 105 dB vocal and compressed it down to a manageable 85 to 93 dB, you may need to increase the output a little to get it over those guitars and drums.  Instead of reaching for the gain or trim knobs (which would then bring more signal into the compressor and would change how you’ve set your compressor), if you add 5 dB of gain to your output you just took that 85-93 dB and made it 90-98 dB.

Compressors are a huge help to the sound man and used right they will help you get great sound out of your sources and give you the ability to place them in the mix.  In a worship environment where the voice of those leading the worship must always be present but not piercing, where more and more guitars are being used to lead the music but can’t overtake the vocals, and where many churches regardless of style use acoustic drums, compressors are the tool that will give you the ability to get the mix where you want it.  I truly believe that no one setting is right for any vocal or instrument.  If you start with a lower basic setting and then adjust based off of what you are hearing, your compressors can give you a great edge to get your mix balanced and layered according to plan.  Just remember, you don’t want to unnecessarily compress something more than you need to, but if you’re having trouble keeping a source in it’s place in the mix the compressor is the tool to help you make that happen.

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One response

29 06 2010
Sandra Greenzweig

‘thank you for this article. It was very informative.

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