Snoring is a prevalent disorder affecting 20-40% of the general population. The mechanism
of snoring is vibration of anatomical structures in the pharyngeal airway. Flutter
of the soft palate accounts for the harsh aspect of the snoring sound. Natural or
drug-induced sleep is required for its appearance. Snoring is subject to many influences
such as body position, sleep stage, route of breathing and the presence or absence
of sleep-disordered breathing. Its presentation may be variable within or between
nights. While snoring is generally perceived as a social nuisance, rating of its noisiness
is subjective and, therefore, inconsistent. Objective assessment of snoring is important
to evaluate the effect of treatment interventions. Moreover, snoring carries information
relating to the site and degree of obstruction of the upper airway. If evidence for
monolevel snoring at the site of the soft palate is provided, the patient may benefit
from palatal surgery. These considerations have inspired researchers to scrutinize
the acoustic characteristics of snoring events. Similarly to speech, snoring is produced
in the vocal tract. Because of this analogy, existing techniques for speech analysis
have been applied to evaluate snoring sounds. It appears that the pitch of the snoring
sound is in the low-frequency range (<500 Hz) and corresponds to a fundamental frequency
with associated harmonics. The pitch of snoring is determined by vibration of the
soft palate, while nonpalatal snoring is more 'noise-like', and has scattered energy
content in the higher spectral sub-bands (>500 Hz). To evaluate acoustic properties
of snoring, sleep nasendoscopy is often performed. Recent evidence suggests that the
acoustic quality of snoring is markedly different in drug-induced sleep as compared
with natural sleep. Most often, palatal surgery alters sound characteristics of snoring,
but is no cure for this disorder. It is uncertain whether the perceived improvement
after palatal surgery, as judged by the bed partner, is due to an altered sound spectrum.
Whether some acoustic aspects of snoring, such as changes in pitch, have predictive
value for the presence of obstructive sleep apnea is at present not sufficiently substantiated.
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