Recording Tips: Compressors

I have been asked many times to share my insights into creating better audio. It’s no secret that many more people today than ever before are doing some sort of recording on their own. The truth to this is that it is a great thing for those of us in the professional audio world (although some disagree). I receive innumerable projects across my desk from those that have recorded something on their own and want to improve it, add to it or work from it. Knowing how to use the basic tools to make better recordings allows these people to spend more time on the creative aspects of what they are recording and less time trying to figure out how to work all of the gadgets that are included in the recording software/hardware they purchased. Over the next few weeks, I will be writing about the usage of some of the most common audio tools used to achieve more professional recordings. I will be writing these as if the reader knows absolutely nothing regarding the tools, so if you are a little more seasoned, stay with me.

When working with voices, there are two pieces equipment that I almost always use, a compressor and an EQ. There are of course a whole host of other pieces that can be added to the audio chain, but these are the basics. For now, I will focus only on the compressor and save the EQ discussion for another day.

While probably the most commonly used audio tool, the compressor is a stumbling block for many people. For some reason, it just seems overly complicated when in actuality it is an extremely easy to understand tool. A compressor is essentially used to even out the volume of a sound source. Naturally, words that are spoken or sung using inflection and pitch will have areas that are louder and some that are much softer. A compressor, used correctly, will bring the space between the loud parts and the soft parts closer together by automatically turning down the loud parts and turning up the soft parts. In order to do this, you have to be able to tell it how to do its job. Before proceeding, I must first tell you that a compressor can do a lot of things and function in many different ways, today I’m only going to focus the most basic settings and controls. I will delve deeper into the other functions another day. The most basic user influenced parameters on a compressor are as follows:

• Threshold – This tells the compressor when to start working. The compressor will start increasing or reducing volume when the audio signal reaches the specified volume of the threshold. If the volume of the sound never reaches the threshold limits the user sets, it will not be affecting the audio at all.
• Ratio – The setting of the ratio determines how much the volume of the compressed areas will be affected. 1:1 being no affect at all, 20:1 being a very considerable amount of affect well past the point of acting as a limiter (also discussed further later). A ratio of 4:1 would mean that if the audio increases 4 dB above the threshold limits that were set the, volume increase would now only be 1 dB.
• Attack – This setting determines how quickly the compressor starts working after the set threshold has been reached. Attack times set to a very fast setting, say 1 millisecond, will almost instantly have compression applied once the threshold is reached, longer attack times will apply the compression more gradually. Remember, the goal when using these audio tools is not to be able to tell that they were applied, just to improve the sound, adjusting the attack time helps with this greatly.
• Decay – This tells the compressor how quickly to release the compression once the sound has crossed back under the threshold. Again, this is used to make this tool subtler. A fast decay time will release the compressor immediately while a slower decay time will gradually decrease the amount of compression.

Since every vocal recording is different, it is hard to give you a defined setting to use, but the compressor is actually very easy to manipulate and knowing what each control does should aid you in tweaking the effect until it sounds right. Your ears are the best tools you have; use them to compare your effected recording to others that sound good to you.