Dynamic range compression
Dynamic range compression (DRC) or simply compression is a signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds by narrowing or compressing an audio signal's dynamic range.
Threshold: The level above which compression is applied to the audio.
Ratio: The amount of compression applied to the audio once it passes the threshold level.
Attack Time: How soon the compressor starts to compress the dynamics after the threshold is exceeded. If volume changes are slow, you can push this to a high value.
Release Time: How soon the compressor starts to release the volume level back to normal after the level drops below the threshold.