Solo string lines split into perceived parts via frequency proximity grouping

Evidence

Music in which grouping of notes together by frequency proximity produces the sensation of a number of parts being played, even though only a single line of music is being performed, includes works for solo instruments such as the Partitas and Sonatas for solo violin by J. S. Bach. … The rather extraordinary string part writing in the final movement of Tchaikovsky’s 6th Symphony in the passage shown in Figure 5.15 is also often noted in this context because it is generally perceived as the four-part passage shown (track 67 on the accompanying CD). This can again be explained by the principle of grouping by frequency proximity. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1627

Categorization

• XREF: Connects to the scale-illusion experiments surrounding the Tritone Paradox, and to the broader auditory-streaming work from the preceding paragraphs; also links listening practice with my stated interest in how attention shapes perceived parts.
• SHARE: Worth sending to a musician friend who plays solo Bach — they may have noticed the effect as a performer and would enjoy the mechanism named.