Shimmer represents _____

• A. Frequency variation across vowels
• B. Changes in vocal loudness
• C. Cycle-to-cycle perturbation in amplitude
• D. Cycle-to-cycle perturbation in frequency

Answer: (C)

Shimmer measures cycle-to-cycle perturbations in the amplitude of the vocal fold vibration. In a steady, ideal voice, each glottal cycle would have the same peak amplitude, but real voices show small variations from cycle to cycle. Shimmer captures these small amplitude fluctuations, reflecting how consistently the vocal folds close and how stable the glottal output is from one cycle to the next. This is different from changes in pitch (frequency) or from overall loudness changes across a segment. Therefore, the description that matches shimmer is cycle-to-cycle perturbation in amplitude.