It’s worth noting that, on its own, dynamic range compression (DRC) merely reduces the volume of loud sounds above a certain threshold. But it’s not usually used on its own. The added headroom provided by DRC enables the use of additional makeup gain (MG), which turns up the volume of the whole signal after the compressor, including the noise floor. The end result is that the loud sounds are just as loud as they would’ve been before DRC+MG, but the quiet sounds are louder than they would’ve been, making the overall average volume over time also higher, which is what we tend to perceive as “loud”.

Beyond any potential health effects, DRC also just sounds bad after listening for more than a few seconds. It kills the liveliness of the audio and the signal-to-noise ratio.

So why is it used? Loudness is like candy to your ears, we are drawn to it and people tend to perceive louder music as sounding better, even if it’s exactly the same except for a change to the volume knob. DRC+MG is a bit like turning up the volume knob on your behalf, except it’s worse in almost every way.

One legitimate use case for DRC+MG, and in fact one of the original justifications for its widespread use, was the rise of portable music, where you want to be able to hear all of the instruments even though you are in a loud environment like the subway, for example. But this devolved into the “Loudness Wars”.

Tasteful use of DRC, perhaps without much MG, can also help “glue” an instrument within an audio mix. I might use it on a bass guitar, for example, to keep its volume under control so it stays in the background, providing rhythm, and doesn’t accidentally become the lead.

Ideally, the base format for all audio would have little to no DRC, but there would be other versions or built-in metadata to help playback devices adjust the listening experience to the environment by enabling DRC when it makes sense to do so or if the user wants it. Just as movies can be watched with or without HDR and subtitles. Unfortunately, the audio world hasn’t progressed much in that direction.