Underamplify

In general, there is a tendency to underamplify the extreme ends of the musical scale and to overamplify certain particular frequencies below the middle, such as originate from acoustic resonance.

Physiological thresholds can differ from behavioral thresholds by ±15–20 dB HL. Thus, without verification of behavioral responses with amplification, hearing aids may underamplify or overamplify.

What is interesting to note here is that the 2⁄3 gain can be seen to overamplify over the curved line of the impaired ear more than underamplifies, whereas the 1⁄3 gain curve illustrates the opposite, where it tends to underamplify sound to the ear.