Spreading a sound’s energy across more critical bands increases perceived loudness without raising intensity

Evidence

The first effect is that the ear seems to lump all the energy within a critical band together and treat it as one item of sound. So when all the sound energy is concentrated within a critical band, the loudness is proportional to the total intensity of the sound within the critical band. … As the ear is sensitive to sound pressures, the sound intensity is proportional to the square of the sound pressures, as discussed in Chapter 1. Because the acoustic intensity of the sound is also proportional to the sum of the squared pressure, the loudness of a sound within a critical band is independent of the number of frequency components so long as their total acoustic intensity is constant. When the frequency components of the sound extend beyond a critical band, an additional effect occurs due to the presence of components in other critical bands. In this case, more than one critical band is contributing to the perception of loudness, and the brain appears to add the individual critical band responses together. The effect is to increase the perceived loudness of the sound even though the total acoustic intensity is unchanged. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 665

Categorization

• DEFINE: Clarifies what a critical band is and how it functions as a unit of loudness perception.
• QUESTION: Worth chasing: how does the brain ‘add’ critical band responses — linear summation or something more complex?
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 665
• XREF: connects to: Loudness rises once noise bandwidth exceeds the critical band at constant SPL.; Uniform exciting noise delivers equal intensity to every critical band — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1189; Loudness is the summed specific loudness across critical-band rates, not the raw spectral level (+9 more)

Broader Connections

• Loudness grows with bandwidth via area tradeoff except at extreme levels #exemplifies (0.90) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1288
• Perceived loudness and physical sound intensity follow different, non-intuitive mathematical scales #expands (0.85) — George Michelsen Foy, Zero Decibels, 53
• Perceived loudness does not map one-to-one onto acoustic amplitude #corroborates (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 616