Compressors

So we had a short conference with Terry Virgo this weekend, that I had to do sound for at Ferndale High School. At the beginning of the year I scaled down the gear to make the system easier to set up, but for the conference I wanted to have use of a compressor or 4, so I took one with. I thought I would put up a quick post to tell you why, and briefly explain how to setup and use a compressor.

Ok, so before we look at why I hear some of you asking, “what the heck is a compressor?”
A compressor is a dynamic range signal processor, or in simpler terms, its an automatic volume control. It basically reduces the difference between the softest and loudest parts of a signal (the dynamic range)
So the reason I wanted to have use of a compressor was to reduce the dynamic range of an instrument, or in this case, vocals.

Most vocalists are pretty dynamic, they sing very loud sometimes and very soft sometimes. Usually these differences are desirable… i.e. if the song is quiet and/or mellow the vocalist is probably not meant to screaming at the top of their lungs, unless you are into that kind of alternative music!? Sometimes however there may be times when a vocalist is quiet on a word or two in a line because they run out of breath or the word is just not as loud as the rest. When you put a bunch of other music behind that vocal, that word or two disappears into the beautiful mesh of skillfully played instruments! You could turn the vocal up, so that even the quiet words are loud enough to hear, and to be honest, this is what most church sound engineers are doing, or else they get an earful… “We can’t hear the worship leader!” Unfortunately what this means is that the vocal is then too loud on all the other words in the line, and you end up with the classic ‘church’ sound all vocals and nothing much else.
Having a compressor means that you can automatically turn the level of the loud words in the line down automatically so that the vocal isn’t always too loud, but we can still always hear it. I’m going to leave the details of how it actually does that for another day!

Hooking it up!

Firstly, you will need a compressor… at G1 we have a couple of Behringer MDX4600‘s and that’s what I will use to explain with.
Next you will need an insert cable, which looks like this:

Choose which channel you want to use the compressor on, lets say your lead vocal is in channel 12, then plug the TRS jack end of the insert cable into the insert for channel 12, in this image of the Soundcraft GB2R16 we use at G1, its labelled “INS”

Then plug the other 2 ends, as labeled in the cable diagram above into the compressor. Make sure the compressor has power and is tuned on..!

Here is my crash course in setting the parameters on the compressor for vocals:

  • Start by resetting all the parameters:

Expander/Gate: OFF
Threshold: +20
Ratio:  1:1
Output: 0
Limiter: OFF

  • Get the level going into the channel set to the normal level for optimum gain structure (If you’ve been to one of the training days this has been explained)
  • Set the ‘ratio’ to around 4:1
  • Slowly bring the ‘threshold’ down until you are getting around 3dB of gain reduction on the loud parts

Thats about it, you may need to increase the output slightly to compensate for the reduction in gain.

Shoot me some comments if you have questions… i’m gonna eventually do a video of all this so you can see it, and hear it a lot better…

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