the Fletcher-Munson curve

The Fletcher-Munson curve shows how our ears perceive loudness at different frequencies. It reveals that the human ear is more sensitive to mid-range sounds (around 2-5 kHz) and less sensitive to very low or very high pitches. Therefore, a tone at a certain volume may sound loud in the mid-range but softer at bass or treble frequencies. This understanding helps audio professionals set equalization and volume levels so that music or speech sounds balanced and natural to our hearing, regardless of the pitch.