Sound frequency analysis and the site of snoring in natural and induced sleep

The aim of this study was to compare the snoring sounds induced during sleep nasendoscopy, and to compare them with those of natural sleep using sound frequency spectra. The snoring of 16 subjects was digitally recorded during natural and induced sleep, noting the site of vibration during sleep nasendoscopy. Patients with palatal snoring during sleep nasendoscopy had a median peak frequency at 137 Hz (118 snore samples). The peak frequency of tongue-base snoring was 1243 Hz (10 snore samples), and simultaneous palate and tongue was 190 Hz (six snore samples). The median power ratios were 7, 0.2 and 5 respectively. The centre frequencies were 371, 1094 and 404 Hz respectively. Epiglottic snores had a peak frequency of 490 Hz (five snore samples). Comparison of the induced (n = 118) and natural (n = 300) snore samples of the 12 palatal snorers showed a significant difference in both the power ratio and centre frequencies (P = 0.031 and P = 0.049). The peak frequency position was similar (P = 0.34). Our results indicate that induced snores contain a higher frequency component of sound, not evident during natural snoring. This is consistent with an element of tongue-base snoring. Although there is good correlation generally, sleep nasendoscopy may not accurately reflect natural snoring.