Dynamic range compression is a signal processing technique that amplifies quieter sounds or reduces the volume of louder sounds by compressing a track’s dynamic range. This is a broad area of engineering that modifies the dynamics of the track to improve tone quality and assist in ‘gluing’ a mix together.
Adding compression and modifying the dynamics of a tracks will assist in establishing tone and character to the instrument by sharpening and consolidating the waveform. It will also help reduce background noise and improve overall loudness issues as it alters the dynamic range. The application of compression to a track will vary in type and intensity based on the needs and creative direction of the project.
Devices performing compression will usually have controls for setting the loudness threshold, compression ratios, attack times and release times.
Compressors, Limiters and Multi-Bands directly focus on either reducing the volume of loud sounds or amplifying quiet sounds by narrowing (or compressing) the audio signals’ waveform and dynamic range. Limiters have a much higher compression ratio (generally 20:1 and above) and a faster attack time, which increase volume gain without permitting much of the signal to pass a set threshold and limits the signal to a certain peak level, preventing audio clipping.
Compressors and limiters are identical in practice but differ in degrees of application and perceived effect, generally having higher compression ratios and attack times to facilitate variable-gain compression as the loudness of a signal is changed very quickly to prevent the waveform from going over a certain level.
Multi-Band compressors further enhance this by allowing you to focus on reducing or gaining volume for certain sound frequencies instead of the entirety of the audio signal.
Expanders and Gates are the polar opposites of compressors and limiters respectively, and assist in eliminating background noise or sound bleeding from other sources. It mutes a signal that drops below an audio threshold opposed to compressing or limiting a signal that rises above the nominated threshold.