It has been about two years since I wrote on compressors. I am re-addressing this subject because, in the last two years, I have learned a lot about the use of this piece of outboard gear, and I would like to share that information with you all. I think of myself as a sound expert, but that doesn't mean I am not constantly striving to improve my audio techniques. Very much like faith, audio is not stagnant. We should all be learning more and honing our skills as long as we are in the biz.
Before we jump in, I would like to send a shout out to Chris Onsrud, the director of production at Gloria Dei Lutheran Church. Chris wrote me about his experience after reading my "Inviting a Pro" piece. He befriended a genuine road dog and invited the tat covered, black attired, front of house expert to mix at his church. He said the results were excellent. As the writer of "Sound Sanctuary," it is always gratifying to hear that some of my suggestions work out in the real world of worship sound. So, here's to ya Chris. Thanks for the email. (By the way, if you want to read the entire email, it is posted at jamierio.com under "shout outs.")
All right, let's get on with this month's installment. You probably have a compressor/limiter in your outboard rack or it's built into your digital board. If you do not have a compressor/limiter, this article may encourage you to purchase one. A compressor is also known as a dynamics processor. It's designed to control the volume, or dynamics, of the audio waves traveling through it. A properly-engaged compressor can improve the intelligibility of the spoken word, the singing voice and control where instruments are placed in the overall mix.
Most compressors incorporate a limiter. The limiter section of the compressor creates a ceiling on the overall audio signal. In general, the limit knob adjusts the threshold where the limiter takes control. Limiting can range from 8:1 to 20:1 or even infinity. This steep audio level reduction is necessary to put a lid on an excessive audio signal. Attack times are pre-set as fast and release times slow enough to create a smooth limiting effect. If you are limiting an individual vocal or instrument, use your ears to reach a satisfactory level. Many limiters are used to put a cap on the entire audio mix. Brick wall limiting is very much like it sounds – the signal hits a brick wall when it passes the threshold and will go no further. It keeps the loudest of sounds from overdriving and ultimately distorting the FOH speakers. The limiter section operates independently of the compressor.
Five Parameters
To understand how to properly use a compressor/limiter, we will need to understand the parameters of this piece of outboard gear. I don't have the space here to go into detail about individual models and makes of compressors, but I will touch on the five main elements of compression. They include threshold, ratio, attack, release and gain (or gain makeup).
The "Threshold" is the point where compression begins. Typically, twisting your threshold knob to the right will raise the dB level that the compressor kicks in. Turning this knob to the left will, of course, lower the dB level that the compressor engages. Setting your threshold high will only compress the higher-decibel levels of your audio signal. As you lower the threshold, more of the audio signal will be compressed. Start with your threshold knob in the center position. This is a good place to begin. Then use your ears and listen to what happens as you raise or lower the threshold.
"Ratio" is the difference in decibel reduction from the input signal to the output signal. A typical compressor's ratio knob ranges from 1 to 10. For example; setting the ratio at 2 creates a 2 to 1 ratio (2:1). This means that if 2dB of signal enters the compressor, 1dB exits. A 3:1 ratio lets 3dB in and 1dB out. Using these two controls, we can now adjust at what level we capture the signal and how much we compress it.
"Attack" controls how fast the signal is captured. Attack operates in milliseconds (ms). An example of a very fast attack would be 10-25ms. This is good for removing the sibilance, or "sizzle," from vocal, making it more intelligible. Slower attack times have a multitude of uses. Slow the attack time and to use your ears. There is a lot to hear.
Now that you have captured the audio signal, you have to decide when to release it. The "release" knob does just that. The release is also calibrated in milliseconds. A fast release time will cause the compressor to follow the audio signal closely so that rapid input changes (ratio) will not be lost during compression. The slower release times tend to smooth out the overall compression effect.
Finally, all the dynamic processing of compression will reduce signal level. Because of this, manufacturers add a "gain" control to their compressors in order to add back level.
Practical Applications
Now that you have an idea of how to set up your compressor/limiter, I want to share some of my uses and settings with you. Lately, I have been mixing some dynamic and forceful preachers. If I set my ratio from 4:1 to 5:1 and set my attack time to fast and release time to medium, I can really control how the sermon/ message is heard by the congregation.
Everyone wants to hear the pastor clearly. A limiter is also very helpful here, if it is use judiciously. You don't want to squash the preacher's voice – and a little goes a long way.
I have also been compressing the entire choir section. Using a ratio of 3:1 with a medium attack and medium release has given me more control over the entire choir. With the choir, I group the channels (hopefully your mixer has sub groups) and run the group through my compressor.
I also always like to compress my kick drum and bass guitar. Fast attack and release settings, using a ratio of 4:1 to 6:1, have consistently proven to work well on these to instruments. Currently, I'm treating my acoustic guitars with the same setting as my choirs with good results.
Lastly I group my brass sections and use a 5:1 ratio with a medium attack and release. I don't actually have any house of worship brass sections. But I run across them regularly in my secular sound gigs.
Remember to listen carefully to the nuances of compression. You should have very satisfactory results. Good luck…
