Pipe organ stops can reinforce non-octave harmonics to reshape timbre

Evidence

Pure tones appear relatively rarely in nature. Only some bird songs and the sounds produced by a flute can be considered to be pure tones. Most of the instrumental sounds in music are composed of a fundamental tone and many harmonics. The difference in timbre produced by different musical instruments depends on the frequency spectra of their harmonics. Whereas a flute produces primarily one single component, the fundamental, a trumpet produces many harmonic partials and therefore elicits a much broader masking effect than a flute. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 449 (#expands, via linked claim)

One does not always want to maximize energy flow across junctions between two parts of a system. We need the impedance mismatch at the bell end of a trumpet or clarinet to cause reflections and define its resonance frequencies. Impedance mismatches are carefully controlled to achieve desirable timbre in wind and string instruments. For string instruments, large mismatches are required at the points between which strings are stretched, lest the vibrations drain away too rapidly, rendering the string frequencies ill-defined. The infamous wolf note of cellos is a breakdown of this requirement (see section 18.7)—a near impedance matching where none was wanted. — Eric J. Heller, Why You Hear What You Hear- An…, 83 (#corroborates, via linked claim)

Categorization

• corroborated: 2 independent passages support this claim
• XREF: connects to: Organ pipes’ timbre arises from resonances cooperating with edge tone; A tapping bridge adds trumpet-like harmonics to a bowed monochord; Overblowing a pipe jumps its pitch to the next resonator-supported harmonic — David Howard, Jamie Angus, coustics and Psychoacoustics, 1211 (+9 more)

Broader Connections

• Instrument timbre differences stem from harmonic spectra that shape masking breadth #expands (0.80) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 449
• Instrument design exploits impedance mismatches to create resonance and timbre #corroborates (0.75) — Eric J. Heller, Why You Hear What You Hear- An…, 83