Even identical instruments playing in unison produce uncorrelated waveforms.

Evidence

On the other hand, if the sound waves are uncorrelated, then they do not add algebraically, like correlated waves; instead, we must add the powers of the individual waves together. As stated earlier, the power in a waveform is proportional to the square of the pressure levels, so in order to sum the powers of the waves, we must square the pressure amplitudes before adding them together. If we want the result as a pressure, then we must take the square root of the result. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 244 (#expands, via linked claim)

Categorization

• XREF: connects to: Uncorrelated sound waves sum by power, not by amplitude. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 244; Acoustic instrument sounds constantly change even during steady-state portions; Even identical notes vary measurably across every repeat performance (+4 more)

Broader Connections

• Uncorrelated sound waves sum by power, not by amplitude. #expands (0.95) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 244
• Acoustic instrument sounds constantly change even during steady-state portions #corroborates (0.85)
• Even identical notes vary measurably across every repeat performance #corroborates (0.85)
• Even steady-state musical notes vary in amplitude envelope over time. #corroborates (0.85)
• The power spectrum is blind to the relative phase of a sound’s components #expands (0.80)
• Auditory spectra differ from power spectra for identical sounds. #expands (0.80)