“Roughly, the critical band is the band of audio frequencies within which a second tone will interfere with the perception of the first tone by auditory masking.” – Wikipedia
Critical Bandwidth is the most imporant result from psychoacoustics as it relates to music. It helps us understand why halfsteps generally sound bad… but so do wholesteps and even minor thirds sometimes! AS well, it helps us differnetiate between the roughness of a tritone, which is not physical, versus the roughness of beats, which is physical.
Frequency envelope
Linear Distinct: little to no overlap
Non-Linear Roughness or Beats: moderate to strong overlap
Critical Bandwidth