Compression is a unique tool that is necessary for processing music. The problem most people face is squashing the audio wave they are working with because they use to much compression. Another problem is the simple fact that not many people, especially those who are new to audio work, really know how to work all of the scary knobs on a compressor. Many of you may not even know what a compressor is used for, and that is perfectly fine… for now.
There are no exact numbers that one can use to set compression levels. Compression and all other facets of audio work are artistic. Like all artistic work, compression requires a large amount of feeling and personal taste. This leads me to the obstacles that stand with our initial issue of compression.
Understanding compression comes from digging a little deeper, and learning all of the core parts to a compressor. Compression is basically a volume knob that is controlled automatically over time (throughout the track). In order for the compressor to work automatically and effectively, the audio technician must know how to adjust the five core parts, and what they do.
Beginning with the most important part, the lower the threshold the more signal is treated. A higher threshold reduces only the loudest parts.
The ratio should be adjusted next. The ratio controls the strength of the compressor. In order to analyze the concept of a ratio we must look at ratios! A ratio at 3:1 will be much different from a ratio that is 10:1. For every 3 decibels over the threshold the audio would only be allowed to go over 1 decibel. This is a fairly light reduction. 10:1 is a very heavy reduction and the same concept applies. The higher the ratio the more squashed the audio will sound, which we generally like to avoid. We want the life or soul to still live in our sound.
Attack is all about the speed of the compressor. It is quite simple, a fast attack creates a fast reduction, and a slow attack will take longer for the signal to be compressed until the ratio is reached. Faster attack can make the sound duller, but it can also tame louder sounds. A slow attack really emphasizes the transients in the audio.
Release is the opposite of the attack. The release knob adjusts how quickly or slowly the level returns to uncompressed once the signal falls back under the threshold. A fast release often causes a very unnatural breathing sound also known as pumping. If it is set to slow the compressor will never reach an uncompressed level. Generally, the attack is more important than the release, but we must avoid pumping!
Finally, the makeup gain. This is the output control. Compressors reduce the louder parts of the track which affects the overall volume of the track. The loud sounds are being decreased, while the soft sounds are boosted. Make up gain is touchy because the audio has to be loud enough, but you don’t want to boost unwanted frequencies that can make listeners subconsciously feel anxious, which is a real issue that audio technicians face.
Now that we’ve touched base on all the different aspects of the compressor, the only way to become better is to apply the knowledge, and practice on the audio tracks. Compression is all about shaping the soundwaves, and controlling how they sound. Here is a general guideline to setting the compression. Remember these are all just good places to start, and will more than likely require some additional tweaking.
| Ratio | 2:1 is light reduction | 4:1 is moderate reduction | 8:1 is heavy reduction |
| Attack | 1-5 ms is fast/short | 5-10 ms is medium | 10-20 ms is slow/long |
| Release | 1-10 ms is fast/short | 10-50 ms is medium fast | 60-100 ms is slow/ long |
What effects have all of you gotten from adjusting the compression on audio tracks? Who is your favorite producer who has mastered compression techniques? Mine is Sir George