Applying independent vibrato to partials splits one complex tone into two perceived instruments

Evidence

In figure 23.31, we see the spectrum of an ordinary complex periodic tone, with every other partial colored red, beginning with the second partial. This tone “ought” to have an unambiguous, strong pitch at frequency f. Yet who is to say that the tone is not a combination of two tones? The lower tone consists of the black power spectrum, and the upper tone the red power spectrum. Both tones are complex, one an octave above the other. A tone like this could be produced with a combination of a clarinet (lacking its even partials) playing a G3 (black spectrum) and an oboe an octave above, playing a G4 (red spectrum), with all its overtone partials present. A clever experiment was described in a Stanford PhD thesis by S. McAdams. The harmonics of an oboe were separated into even and odd components, and then an independent vibrato was added to just the odd components. This results in the sensation of two independent notes on two different instruments, separated in pitch by an octave. — Eric J. Heller, Why You Hear What You Hear- An…, 2173

Categorization

• CANDY: A clean party fact: separate the even and odd harmonics of a single oboe, give the odd ones their own vibrato, and you hear two oboes an octave apart — pure reconstruction of perception.
• QUESTION: The McAdams result is a striking evidence point for how grouping cues (common vibrato) drive auditory scene analysis — worth pursuing the original thesis for mechanism details.
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 2173
• XREF: connects to: Accentuating individual harmonics makes them perceptually break away as separate notes; Alternating timbres can split a single melodic line into separate perceived streams — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1629

Broader Connections

• Accentuating individual harmonics makes them perceptually break away as separate notes #complicates (0.85)
• Alternating timbres can split a single melodic line into separate perceived streams #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1629