Spectral envelope analysis in snoring signals from simple snorers and patients with Obstructive Sleep Apnea

Several studies have shown a relationship between snoring and obstructive sleep apnea syndrome (OSAS). Beyond conventional sound intensity analysis, some spectral differences have been found between snores from simple snores and post-apneic snores from OSAS patients. Snoring spectrum has two components, a fundamental frequency and a spectral envelope. Spectral density studies analyze them altogether. In this work we approach the estimation of the spectral envelope alone, which is closely related to the mechanism of snoring production. Linear prediction autoregressive (AR) modeling with a low order is used for spectral envelope estimation. Two methods are proposed for automatic order estimation. Formant frequencies of the spectral envelope are calculated. A total of 447 snores from 8 simple snorers, and 236 normal and 429 post-apneic snores from 8 OSAS patients are analyzed. Significant differences are found (p<0.005) in formant frequencies variability between simple snorers and OSAS patients, even when non postapneic snores are considered.