Current evidence for the existence of laryngeal macrotremor and microtremor

To test for the existence of laryngeal "microtremors" two experiments were conducted on humans. The first analyzed the acoustic characteristics of observable tremors (macrotremors) in the voice of singers using vocal vibrato and in pathologic subjects producing vocal tremor. In both of these groups acoustic oscillations between 4 and 8 Hz were found. The second study, using a normal subject, sampled electromyographic (EMG) activity from laryngeal and arm muscles during isometric contraction to determine if a periodic component (microtremor) was present in either muscle's contraction pattern. A 9-Hz signal was detected in limb muscle contraction, whereas no periodicity was found in signals from laryngeal muscles. The application of these findings to the theory behind voice "stress" analyzers is discussed