SoX is a great tool for converting and processing audio. As an engineer working at a radio station I find it especially useful for processing audio files so the volume is even and smooth throughout. A recent use case was preparing news bulletins recorded by a non-technical journalist so they sounded clear and loud for an Amazon Alexa skill.
Automatic Gain Control (AGC) is an audio processing technique that is designed to smooth out volume differences between different parts of an audio programme. The majority of radio stations will have a device at their transmitter (for example, an Optimod) that does just that. Parts of the broadcast that are two quiet are boosted and parts that are too loud are atenuated.
For those familiar with audio [compressors