Today we are going to discuss dynamic range compression. To be more specific, I’m going to talk about the one that ships with Audacity, since that’s the one I use. A dynamic range compressor, called the compressor in Audacity, attenuates the louder frequencies, reducing the differences between the loud and soft passages in a piece of audio. In layperson’s terms, it makes the loud passages quieter and the quiet passages louder. When you open the compressor in Audacity you will see that it has settings for the Threshold, the Noise Floor, the Ratio, the Attack Time, and the Decay Time. We will take a whirlwind tour of each of these features.
The Threshold setting determines the starting point, in decibels, where the gain of the audio signal is reduced. The Noise Floor is the measure of the signal created from the sum of all the noise sources of the piece of audio under question. The ratio setting determines how much compression will be applied. The Attack Time setting determines how quickly the compressor reaches its maximum effect. The Decay Time setting determines how long it takes to phase out the compression. These setting are all discussed and illustrated with screen shots in the comprehensive (3,700 words and counting) digital audio dictionary I am compiling.
Another dynamic range compressor was developed by the late Chris Capel because he wanted to apply compression to his recordings of classical recordings. His site is now being maintained by Daniel Lewis. You may download Chris’s Dynamic Compressor as a plug-in for Audacity here: http://theaudacitytopodcast.com/chriss-dynamic-compressor-plugin-for-audacity/ .