Mixing at the Right Levels
There’s this theory of the ear that it hears different frequencies at different levels. The Fletcher-Munson curves, commonly known as equal-loudness contours, indicate the ear’s average sensitivity to different frequencies at various amplitude levels.
Even if the tonal balance of the sound remains the same, at low volume, mid range frequencies sound more prominent. While at high listening volumes, the lows and highs sound more prominent, and the mid range seems to back off.
In short, this explains why quieter music seems to sound less rich and full than louder music. Generally it’s better for the music to sound good as the volume increases.
As a consequence of this, you should edit, mix and work on your music on a high enough volume (not ridiculously loud), so that you can make sure your music doesn’t sound terrible when it’s listened to at a higher level. Because as a music producer you would want your music to sound best when the listener is paying full attention. But use caution, don’t damage your ears bla bla bla.