Action tremor Vocal tremor 2013-11-28T07:11:37Z A wavering, unsteady voice that reflects involuntary and approximately sinusoidal oscillation of motor unit firings of laryngeal muscles. Vocal tremor results in low frequency modulations of voice frequency or amplitude and intermittent voice instability. Vocal tremor HP:0012477 UMLS:C4022889 Shakey voice