Just Noticeable Difference, JND for short.
We all sort of know this just by being listeners, but the concept of Just Noticeable Difference wasn’t a topic I’d seen mentioned on the forums, and I thought I’d give it a shout out.
The wikipeida article about JND – not a great article in itself – begins:
Just Noticeable Difference
in the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, > a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable at least half the time (absolute threshold).>  This limen is also known as the difference limen, differential threshold, or least perceptible difference.
Music production applications
In music production, a single change in a property of sound which is below the JND does not affect perception of the sound. For amplitude, the JND for humans is around 1 dB (Middlebrooks & Green, 1991; Mills, 1960).
The just-noticeable difference (JND) (the threshold at which a change is perceived) depends on the tone’s frequency content. Below 500 Hz, the JND is about 3 Hz for sine waves, and 1 Hz for complex tones; above 1000 Hz, the JND for sine waves is about 0.6% (about 10 cents). The JND is typically tested by playing two tones in quick succession with the listener asked if there was a difference in their pitches] The JND becomes smaller if the two tones are played simultaneously as the listener is then able to discern beat frequencies. The total number of perceptible pitch steps in the range of human hearing is about 1,400; the total number of notes in the equal-tempered scale, from 16 to 16,000 Hz, is 120.
JND is briefly related to amplitude and to pitch, but anything – EQ, Compression, FX, Pan – will have a just noticeable difference factor as well. I’m finding it interesting to see how JND relates to the Equal Loudness Contour.
Aside from possible engineering use, JND, also applies to product marketing. Consider this when asking for new features or re-asking for things you still believe should be part of Cubase but are not.