Sensory dissonance is the roughness caused by beating partials within the critical band

Sensory dissonance (CDC-5 in Sethares’ classification) is the perceptual roughness that arises when partials of simultaneously sounding tones fall within each other’s critical bands and produce audible beats. It was modeled by Plomp and Levelt (1965): pairs of sine waves are most dissonant when their frequency difference is about 1/4 of the critical bandwidth, and nearly consonant once the separation exceeds the full critical bandwidth. Sensory dissonance is distinct from functional dissonance (the harmonic tension of music theory) — a minor seventh may be functionally dissonant but have low sensory dissonance with suitable timbres. The Plomp-Levelt curves have been replicated across cultures, suggesting sensory dissonance is a psychoacoustic universal, even if cultural factors shape musical practice.

Examples

A major triad with harmonic timbres has low sensory dissonance because harmonics align at consonant ratios. The same chord played with strongly inharmonic timbres may have high sensory dissonance even if the fundamental ratios are the same. Conversely, an interval that sounds functionally dissonant (e.g., a major 7th) may have low sensory dissonance if the timbres are chosen carefully.

Assessment

Explain the difference between sensory dissonance and functional/contrapuntal dissonance. Give an example where (a) an interval has high functional dissonance but low sensory dissonance, and (b) an interval has low functional dissonance but high sensory dissonance (hint: think about timbre).