Understanding compression

In mastering, the Compressor is the primary way of raising the relative level of the program and giving the master both punch and strength. Relative Level is how loud we perceive volume, rather than the Absolute Level, which is what's displayed on the meter. Usually, the ratio of the mastering compressor will be set very low from about 1.5:1 to 3:1 in order to keep the compression fairly gentle sounding. The higher the ratio, the more likely is that you'll hear the Compressor working, and it will sound unnatural.

(music playing) The key to getting the most out of the Compressor is the Attack and Release controls, which have a tremendous overall effect on the mix and therefore are important to understand.

Generally speaking, transit, response, and percussive sounds are affected by the Attack control setting. Release is the time it takes for the gain to return to normal or zero gain reduction. In a typical pop style mix, a fast attack setting will react to the drums and reduce the overall gain. (music playing) If the Release is set very fast, then the Gain will return to normal quickly.

This can result in the audible effect of reducing some of the overall program level and attack of the drums in the mix. (music playing) As the release the set faster any gain changes that the drums caused might be heard as pumping, which means that the level of the mix will increase then decrease noticeably.

Each time the dominant instrument starts or stops, it pumps the level of the mix up and down. Listen to this example of a mix that exhibits a lot of pumping. (music playing) Compressors that work best on a full range of full program material generally have very smooth release curves and slow release times to minimize the pumping effect.