The ear’s amplitude sensitivity varies with loudness and tonal complexity

Evidence

For pure sine waves, however, the sensitivity to change is markedly different and is a strong function of both amplitude and frequency. For example, at 1 kHz, the just-noticeable amplitude change varies from 3 dB at 10 dB(SPL) to 0.3 dB at 80 dB(SPL). … This variation occurs at other frequencies as well, but in general, the just-noticeable difference at other frequencies is greater than the values for 1 to 4 kHz. These different effects make it difficult to judge exactly what difference in amplitude would be noticeable, as it is clearly dependent on the precise nature of the sound being listened to. There is some evidence that once more than a few harmonics are present, the just-noticeable difference is closer to the broad-band case, of 0.5 to 1 dB, rather than the pure tone case. As a general rule of thumb, the just-noticeable difference in sound level is about 1 dB. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 648

Categorization

• XREF: connects to: The ear’s frequency response means quiet playback dulls bass and treble — David Howard, Jamie Angus, coustics and Psychoacoustics, 617; The ear’s just-noticeable amplitude difference depends on signal type, level, and frequency — David Howard, Jamie Angus, coustics and Psychoacoustics, 636