Humans perceive extended sound sources poorly when their parts emit identical tones

Evidence

This section concerns sounds that in some sense could be said to “deceive” the ear. Such sounds have a psychoacoustic realization that is not what might be expected from knowledge of their acoustic components. In other words, the subjective and objective realizations of sounds cannot be always directly matched up. While some of the examples given may be of no obvious musical use to the performer or composer, they may in the future find musical application in electronically produced music for particular musical effects where control over the acoustic components of the output sound is exact. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1568 (#expands, via linked claim)

Engineers have invented several ways to quantify the magnitude of the non-linearity by measuring the distortion products and expressing them as a percentage of the original input signal, or of that signal plus distortion and noise. If the input signal is a pure tone, the distortion products are harmonic overtones of that signal: harmonic distortion. The problem with that method is that as the fundamental frequency gets higher, the higher harmonics move beyond the hearing range so it ceases to be a relevant metric. Combining two closely spaced tones and scanning them to high frequencies is more useful. Each of the tones will generate a set of harmonic distortions, but they will also interact with each other in the non-linearity and create combination tones—intermodulation distortions. These are sum and difference multiples of the two input signals and their harmonics that extend upwards and downwards in frequency. Because masking is much more effective in the upward frequency direction (see Figure 9.14), it is the difference frequencies that end up being more audible and, because they are inherently unmusical, more annoying. — Toole, Floyd E, Sound reproduction- the acoustics and…, 989 (#expands, via linked claim)

Categorization

• corroborated: 2 independent passages support this claim
• XREF: connects to: What the ear perceives can diverge from sound’s physical components. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1568; Upward masking makes intermodulation difference tones more audible than harmonics — Toole, Floyd E, Sound reproduction- the acoustics and…, 989

Related

• Difference noise generated by ear nonlinearities can be heard before the test tone itself (similarity 0.87)
• What the ear perceives can diverge from sound’s physical components. (similarity 0.86)
• Upward masking makes intermodulation difference tones more audible than harmonics (similarity 0.86)
• Hearing’s own nonlinearity produces audible difference tones even in distortion-free equipment (similarity 0.83)
• Groupings of strong adjacent partials constitute what the ear hears as formants (similarity 0.83)
• The ear itself generates distortion products even when equipment is clean (similarity 0.82)
• Prevailing nineteenth-century views treated the ear as receiving motion souvenirs from sound sources (similarity 0.82)
• Combination tones beat against other near-pitched instruments unless masked (similarity 0.82)
• Two simultaneous pure tones may fuse rather than be heard separately. (similarity 0.82)
• Combination tones arise from the hearing system’s own nonlinearity (similarity 0.81)
• The ear generates audible combination tones not present in the stimulus (similarity 0.81)
• Nonlinear cochlear mechanics make listeners perceive nonexistent difference tones (similarity 0.81)
• Interfering noises resembling speech’s modulation fool attention and exceed their level (similarity 0.80)
• Distorted audio gear can create phantom tones falsely attributed to the ear (similarity 0.80)
• Sound denotes both a physical wave and the subjective percept it evokes (similarity 0.80)

Broader Connections

• What the ear perceives can diverge from sound’s physical components. #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1568
• Upward masking makes intermodulation difference tones more audible than harmonics #expands (0.75) — Toole, Floyd E, Sound reproduction- the acoustics and…, 989