FIG. 9.

Frequency-behavior the arrival indicator function I, showing dependence on the variance of the random process describing the arrival phase Φ. (a) I(f) for σ_Φ⪡1 (highly periodic flow), as found in whistling, where the sound field becomes phase-locked to vortex shedding at the separation point, resulting in a spectrum composed of a fundamental (the jet instability frequency, 1/T_arr) and its harmonics. (b) I(f) for σ_Φ⪢1 (highly turbulent flow), as usual in unvoiced speech sounds, where the peak occurs at the jet instability frequency, but which exhibits no tonal quality.