NORAM: calibration and operational advice for measuring nasality in cleft palate patients

This study was carried out to evaluate the NORAM (Nasal-Oral-RAtio-Meter), developed at the Department of Speech Communication and Music Acoustics, RIT. The speech samples used were the recorded speech of normal and nasally deviant speakers. NORAM measures the total speech time and the duration of the nasalized portions, it also calculates the ratio between these two values. The signals are picked up by two contact microphones, one placed on the alar cartilage of the nose and the other on the outside of the lamina of the thyroid cartilage. They are compared and the segment is rated as nasal, if the signal from the nose pick-up is close in intensity to the larynx signal. It was found that the threshold should be set 9 dB below the larynx signal. The reliability of the measurements depends to a large degree on the accurate calibration of the instrument. In sentences lacking nasal consonants, produced by normal speakers, some nasal segments were registered at word boundaries and at the end of phrases. In the patient material these segments tended to be broader and additional segments were also found.