Loudness perception shows distinct behavior in two critical-band-defined regions

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 from those outside its frequency range, and there are consequential effects on the perception of loudness. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 661

In this case, the peak value produced by the three-tone complex does not increase much, and therefore at low frequencies of modulation the equally loud I-kHz tone shows a level that corresponds to the level of the unmodulated tone. This way, the curve shows two clear-cut regions. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1214

Categorization

• DEFINE: Clarifies how critical bands, introduced earlier, shape loudness summing across a spectrum.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 661; Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1214
• XREF: connects to: Consonance and dissonance judgments stem from critical bandwidth mechanics — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 934