Partial spacing determines whether coincidences cause beating, roughness, or fusion

Evidence

If we overlay the partials from each of two tones (figure 26.10) like two combs, in some regions the teeth will be coincident or nearly so. The beating caused by very near coincidences (within a few Hz) will be slow, a little like a vibrato and not objectionable. In other regions, the teeth will be less nearly coincident, causing faster beating and roughness. If the teeth are well separated, corresponding to a large frequency difference, the beating fuses into a single tone. — Eric J. Heller, Why You Hear What You Hear- An…, 2351

Categorization

• QUESTION: Does beating fuse into a single tone perceptually when partials separate widely, and at what frequency gap does this occur?