makeup gain & knee

“So compression makes things quieter? I always thought it was supposed to make things louder!” is what you might be saying to yourself at this point. Technically, a compressor reduces the dynamic range of a signal, and it does so by turning the loudest points of the signal down. Imagine an uncut lawn with its shortest blade of grass at 2” and the tallest at 6”. The dynamic range is the difference between these. When you mow the lawn down to 3”, for example, any blades that were standing more than 3” tall will be cut down but those that were shorter – like the 2” blade – will not be affected by the mower at all. In this case, the dynamic range of the yard has been reduced. When the grass grows (and for the sake of the analogy it will all grows at the same rate), the tallest blades will stand as tall as they were before the mowing but the shortest will also have grown, reducing the dynamic range. The lawn will appear taller now than it was before it was cut, even though the tallest grass is still the same height.

In the same way, the goal of compression is to make the quiet bits in a signal louder. It just so happens that we accomplish this in the two-step process of selectively turning down the loudest peaks before returning them to their original volume by raising everything all at once afterward. Just like the lawn, even if the loudest peak doesn't change its volume, the higher average volume will make the whole signal seem louder.