Of all the processors available for use in mixing audio, the compressor seems to be the most mystified and least understood sound-sculpting tool. In my travels to churches around the country, I have frequently encountered audio-compressors installed in effects-racks that are either not being utilized or are being used incorrectly. In much the same way that a noise-gate used incorrectly can wreak havoc on a mix, an audio compressor is like-wise prone to misuse, if not understood and employed correctly. But why do we need compressor/limiters, you ask? ….isn’t that what our fingers are for ???

The reasons for using compression/limiting in audio mixing are two-fold. The first and foremost reason for the use of compressors is to control or tame dynamic range. In other words, the compressor’s main job is to “narrow” or “lessen” the difference between the quietest levels and the loudest levels of an audio signal. With so many potential sound sources in a typical mix, it is virtually impossible to gain-ride every one. And even if we could do so physically, it is equally as impossible to predict the potential levels of each player or singer’s performance The second reason for employing the use of a compressor is for the purpose of adding character to the sound (i.e. punch, pop, sustain, urgency, and a plethora of other subjective terms used to describe the effect).

If used correctly, multiple compressors inserted across the instrument/vocal channels, can do the subtle, automatic gain-riding needed to smooth-out the transients or dynamic spikes that are naturally present in any given instrument or vocal performance. This is a great way to make things gel and to create space for things to “sit in a mix”. Additionally, the same thing can be accomplished “globally” on a group of instruments by inserting a compressor on a SubGroup or Master Fader, thus adding polish, punch, and sheen to the overall sound of that subgroup or Master fader. If the compressor is used more aggressively (i.e. higher compression ratios, extreme attack or release times, lower thresholds, etc. ), the effect of compression becomes a more noticeable “effect” rather just a subtle reduction of the dynamics. This can add urgency and sustain to a guitar, give “pop” to the bass guitar, and provide “punch” to individual drums, etc..

Again, some caution is in order here, as a compressor that is incorrectly used can do as much harm as it does good! It is imperative that we understand the function of the various controls found on the compressor, and the affect that these controls have on the sounds being processed. It is just as easy to take the life out of an instrument or mix, if taken to extremes or by improperly setting the control parameters of a compressor. Likewise, compressors vary wildly in their sound quality, depending on their design and build quality, and prices vary accordingly. I find that most of the low-end (cheaper) compressors available are a bit heavy-handed in how they handle audio, with more noticeable artifacts evident in the processing. However, even a low-end compressor can be useful if it is carefully and properly adjusted for subtle gain-riding.

As with any audio processor, it is imperative that we have a complete understanding of the uses and abuses of the equipment at our disposal. Read the manuals, watch the YouTube videos, Google it, then experiment with the gear. and use your ears!!

So, I hope this clears-up some the mystery of what compressors/limiters do, and how they affect a mix. Next time, we’ll take a more in-depth look at the various compressor/limiter control-parameters and their functions.

Happy mixing!!

Michael Grosso CCFL Technical director / audio engineer

Tags: homepage

This entry was posted on Thursday, August 6th, 2009 at 2:11 pm and is filed under Gearheads. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.