It applies a volume dependant frequency curve to compensate for how the ear changes as volume is decreased and increase.

If you switch it off and decrease volume, the most obvious difference is bass drops off as the volume gets lower, but the ear doesn’t perceive other frequencies as loud either.

If you enable it, bass and other frequencies are boosted as the volume gets lower, to counteract the perceived drop in frequencies so things sound normal at lower volumes.

There is a point increasing volume where switching it on and off has no noticeable difference because it reduces the effect as volume increases until nothing is being boosted.

This is one of the more difficult human auditory perception concepts to wrap your head around. Basically, the setting enhances the human’s ability to perceive the full frequency range of the music when listening at lower Volume levels.

Here is a basic explanation. Wikipedia has a more complete explanation, but it will probably make your head spin on first read. A complication that virtually no discussion mentions is that the loudness effect varies from individual to individual. Effective loudness compensation for one individual may not be so great for another.

I suggest that you listen to a track that has a full range of frequencies at different Volume levels while flipping Loudness ON and OFF. Only you will know which is the “best” setting (for you).

Great! Thanks for the info on this! I will test it out.