Acoustic Measures of voice Flashcards
What is Jitter
Jitter: Cycle to cycle variability in frequency. For example F0 = 200Hz, most cycles take 1/200
Usually calculated as a percentage of change in frequency./ Normal Jitter = 0.1-1.0
Jitter greater than 1 percent is too much aperiodicity( too many non harmonic partials)
Many reflect interference with fold fold vibration and mucosal wave
What is Shimmer
Shimmer: Cycle to cycle variability in Amplitude, for example average amplitude may be at 100 percent
Not as well studied/ researched as jitter
Usually calculated as a percentage change in amplitudeShimmer greater than 4 percent is too much aperiodicity
May reflect interference with vocal fold vibration and mucosal wave
What are the Perturbation measure challenges for jitter and shimmer
Require high fidelity recording (affected by mic type)
Different software programs and different units
Jitter= percent change ms, Hz, Shimmer= Percent change, dB
Jitter has additional specific changes- need enough cycles to calculate period but if cycles are very variable and may not be able to lock onto signal
Both are affected by loudness
-Jitter and shimmer can be used to measure clinical applications such as ALS, Parkinson’s disease, stuttering and functional voice problems
Describe the Harmonics to Noise Ratio
Proportion of harmonic sound to noise in the voice
Measured in dB = HNR = 20log(harmonic amplitude/ Noise amplitude)
Qualifies the relative strength of harmonics over noise
Higher HNR- harmonic sound dominates over the noise
What is an example of Harmonics to Noise Ratio
For Example: For a person with a vocal fold nodule( or any lesion on VF edge), more air escapes during vibration of folds- more noise.
The excess air causes turbulent noise, creating a lower HNR
High correlation with perception of vocal quality for hoarseness, breathiness and roughness
HNR values for children and elderly adults are lower than for young and middle age adults ( strongly affected by loudness)
Describe Maximum Phonation Time
MPT is the maximum time in seconds for which a person can sustain a vowel sound when produced on one deep breath at a relatively comfortable pitch and loudness
Typically with no laryngeal pathology
Adult males- 25-35 seconds
Adult females- 15-25 seconds
Children are expected to be able to sustain phonation for at least 10 seconds
Decreased MPT may be due to: deficits in respiratory system( lung volume, emphysema) and inefficiency in vocal fold vibration (causing more rapid loss of air)
What is Dysphonia
The general term for any kind of dysfunctional phonation, two very broad categories (hyperfunctional and hypofunctional)
Describe Hyper-functional voice
Hyperfunctional: Due to excessive glottic closure (VFs are pressed together tightly)-
Muscle tension Dysphonia, Adductor Spasmodic Dysphonia and Laryngitis and cancerExcessive glottic closure means: Voice quality = tight pressed rough strained
Less periodic (many non-harmonic partials but they tend to be less than 2.5 kHz) Long closed phase
Describe Hypofunctional Voice
-Due to incomplete glottic closure (paralysis, mass lesion, nodule, poly and cyst, VF bowing)
-Incomplete glottic closure means air escapes ( breathy voice quality) and less periodic (many non harmonic partials add noise to signal > 3 kHz) Low HNR and long open phase
What are the vocal registers
Vocal Registers: These are different modes of VF vibration with three main registers:
Pulse register a.k.a “glottal fry”,
Modal register “chest voice” and
Falsetto register- “head voice”
Describe Pulse register
Configuration of VF’s: VF’s are short and thick with high medial compression
Possible involvement of false VFs, several irregular quivering of mucosal edge in edge in each vibratory cycle called multiphasic closure
Due to low frequency these individual irregular vibrations are audible as creaky quality
Low vibratory amplitude- can’t shout in glottal fry and closed phase is very long (90%)
Describe Modal register
Configuration of VFs : all parts of VFs participate (both body and cover)
Cover is loose, even the body vibrates
Wide range of frequencies, amplitude and longer closed phase then open (60%)
