The brain processes sounds inside a critical band as a single lumped item.

Evidence

Unlike tones, real sounds occupy more than one frequency. We have already seen that the ear separates sound into frequency bands based on critical bands. The brain seems to treat sounds within a critical band differently to those outside its frequency range and there are consequential effects on the perception of loudness. — David Howard, Jamie Angus, coustics and Psychoacoustics, 646

Categorization

• DEFINE: Introduces the ‘critical band as one item of sound’ framing central to loudness.