In recent years, several studies have shown the relationship between snoring and obstructive sleep apnea syndrome (OSAS). Instead of time domain analysis of snoring signal, the spectral features and shapes of snores have been found different in simple snorers and OSAS patients. In this study, we propose a method to differentiate simple snorers and OSAS patients based on spectral envelope estimation of snoring signals. Formant frequencies and bandwidths are computed for both groups and the variation and consistency of the formant distributions are determined. A total of 1400 snoring episodes from 7 simple snorer and 7 OSAS patients were analyzed. Significant differences are found in the variation of formant frequencies of both groups. The results are interpreted from a patophysiological view.