The flute lacks the seventh harmonic that groups it with oboe and clarinet

Evidence

Notes excluding the seventh harmonic sound considerably less “reedy” than those with it; the seventh harmonic is one of the lowest that is not resolved by the hearing system (provided the sixth and/or eighth are/is also present). … The clarinet has a particular timbre of its own due to the dominance of the odd harmonics in its output, and it is often described as being “nasal.” — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1478 (#expands, via linked claim)

This particular example of C4 from the flute begins with a notably “breathy” onset just prior to and as the fundamental component starts. This can be seen in the frequency region of the spectrogram that is above 2 kHz lasting some 70 ms. The higher harmonics enter one by one approximately 80 ms after the fundamental starts. The rather long note onset phase is characteristic of a flute note played with some deliberation. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1478 (#expands, via linked claim)

Categorization

• XREF: connects to: The clarinet’s hollow timbre stems from its half-open bore missing even harmonics.; Of four brass instruments, only the trumpet shows prominent high harmonics; The unresolved seventh harmonic imparts reedy timbre to instruments like the clarinet — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1478 (+1 more)

Broader Connections

• The unresolved seventh harmonic imparts reedy timbre to instruments like the clarinet #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1478
• Flute notes have a characteristic breathy onset with harmonics entering gradually after the fundamental #expands (0.70) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1478