Acoustic Parameters:

May be indicators of neurological disease.  Obtaining acoustical data is vital for diagnosis and intervention.  The measures provide a basis of comparison for the person’s voice before, during, and after therapy.  Measures indicate parameters which should be targeted for therapy. Abnormal acoustic measures may vary across individuals with the same disorder (some may have a high Fo and some a low Fo) and may change in severity with the progression of disease (the parameter is affected most or that contributes the most to speech intelligibility may change with time) . Measures can help determine whether a particular treatment strategy is effective or not.

 Frequency variables:

            1.  Average fundamental frequency: measures the persons speaking fundamental frequency (SFF).  Perceptually this corresponds to pitch.  It is affected by age, sex, and gender. Fo may be abnormally low and may suggest pathology. 

Females have an average Fo of 180-250 Hz; Males have an average Fo between 80 and 150 Hz

            2.  Frequency Variability:  changes in the fundamental frequency.

Fo variability is measured in terms of standard deviations from the        average Fo.  FoSD in normal conversational speech is around 20-35 Hz. For production of the prolongation of a vowel, the FoSD should be around 3-6 Hz. Sometimes Fo variability is measured in semitones called the pitch sigma. Pitch sigma for normal speakers during conversation should be around 2-4 semitones.

 Range the Fo variability that is the difference between the highest and lowest Fo in a speech sample. (22.7 semitones is normal, 16.4 semitones is not normal.)

 Clinical implication: Reduced range is characteristic for neurological problems: vocal fold paralysis or Parkinson’s disease. Reduced range suggests possible laryngeal weakness affecting laryngeal muscles in ALS. Abnormally high frequency variability during the production of a vowel suggests inability to control frequency aspects of vocal fold vibration suggesting neurological pathology 

       3.  Maximum Phonational  Frequency Range (MPFR): Measures the lowest tone a person can sustain to the highest tone a person can sustain.  MPFR is often measured in semitones or octaves. A range of around 3 octaves is normal for young adults. Across ages most MPFRs fall  approximately 30-semitones or 2.5 octaves.

 Males lowest 80Hz and highest 700 Hz; Females lowest135Hz and highest over 1000Hz.

   Clinical Implication:  MPFR reflects both physiological limits of a speaker’s voice and the physical condition of the person’s vocal mechanism and basic vocal ability. Reduced MPFR suggest poor vocal health.

4.      Jitter or frequency perturbation is the frequency variability between cycles of vibration.  Normal jitter is around 1% or less or from .2% to 1%.  High jitter levels suggest that something is interfering with normal vocal fold vibration and the mucosal wave. Measuring cycle to cycle variability of vibration can allow us to detect changes in neuromuscular function of the muscles controlling the vocal folds.  Jitter is related to periodicity of the vocal folds. When Jitter is elevated, this suggests an inability to maintain periodic vibration or the person’s ability to vibrate folds rhythmically.

5.      Formant Frequency Measures: Frequency component amplified by resonator (vocal tract). Acoustic properties that distinguish speech sounds.  The Maxima of harmonic energy.  Typically measured by LPC (Linear Predictive Coding) or spectrographic analysis.

                  F1 related to tongue height; F2 related to tongue advancement

                  F2 transition: change in frequency value of formant over time; reflects change in position of articulators

Amplitude and Intensity Variables

        1.  Average Amplitude Level: the overall level of amplitude during a speaking task. Perceptually this corresponds to loudness.  Normal conversational speech is usually between 65-80dBSPL, with an average around 70dB.  Voice amplitude that a person can generate depends strongly on the vocal Fo. 

  Clinical implications: Amplitude may decrease slightly in older individuals.  Very low vocal amplitude suggests difficulty in opening the vocal folds widely enough and closing them.

            2.  Amplitude Variability is expressed as standard deviation, measured in dbSPL.  Standard deviation of amplitude for a neutral, unemotional sentence is around 10 dB SLP.

            3. Dynamic Range relates to the physiological range of the vocal amplitudes that a speaker can generate from the softest above a whisper to the loudest shout. Normal adults should be able to produce a minimum level of around 30dB and a maximum of approximately 115dB.  A restricted range may prevent a person from using stress and emphasis patterns appropriately.  Dynamic range depends on the Fo produced and tends to be greatest for Fo in the midrange and less for Fo that is much lower or much higher.

 Clinical implications the dynamic and phonation ranges determine the physiological limits of the voice because they are directly related to the person’s ability to control the vocal folds.

Clinical implications for neurological disorders:

            PD
            -higher than normal Fo

               -lower SD of frequency and amplitude

                -decreased phonational and dynamic ranges

 Neurological disorders

-         less able to use Fo effectively to distinguish between declarative and       interrogative sentences.

Perceptual characteristics:

-monopitch, monoloudness, inappropriate stress characteristics

4.      Shimmer or amplitude perturbation is the amplitude variability between cycles of vibration.   Shimmer values below .5 dB are normal.  Measuring cycle to cycle variability of vibration can allow us to detect changes in neuromuscular function of the muscles controlling the vocal folds.  Shimmer is related to periodicity of the vocal folds. When Shimmer is elevated, this suggests an inability to maintain periodic vibration or the person’s ability to vibrate folds rhythmically.

            Jitter and Shimmer Clinical implications:

            Document vocal function for neurological disorders such as ALS, PD

            Increased jitter and shimmer in ALS show degeneration in the speech muscles before the degeneration is actually heard as impaired speech. Jitter and Shimmer have been used as outcome measures for different types of treatment for PD.  Acoustically PD have higher Fo, high jitter, low intensity, decreased phonational range and dynamic range.

Duration measures:

  1. Speech rate: measured in syllables per second The time required to complete the sentence “You wish to know all about my grandfather” should be less than 2 seconds with normal variabiit in syllable duration and amplitude (energy tracing), and normal variability and declination in Fo across the sentence (pitch tracing).
  2. Diadochokinetic Rate:  /pa/, /ta/, /ka/ norm is 5-6 syllables per second
  3. Voice Onset Time: measurement of time between stop release and vocal fold vibration.

Multidimensional Visi-Pitch,

            VTI (voice turbulence index suggesting incomplete glottic closure, SPI (soft phonation index suggesting weak vocalization  or phonation), and DSH (degree of subharmonics) are typical for diplophonic voices and voices with glottal fry.

Application for Motor speech disorders:

            Voice and Tremor

Task “ah”

VFo: Coefficient of variation of Fo which is the Fo variation or SD of period to period             calculated Fo for long term variations

            Norm: 0.5%- 0.69%

VAm: Coefficient of variation for amplitude or the peak amplitude variation for long-    term variation

            Norm 1.8% - 6.7%

MFTR magnitude of frequency of tremor

            Norm: 0.2%- 0.3%

AFTR magnitude of amplitude of tremor

            Norm: .7% - 1.6%

Diadochokinetic Analysis: task Say “puh-puh-puh…”

DDKavr: syllables/second; norm = 5.97 -6.22 (Disordered speech is usually slow)

DDKcvp: Coefficient of variation of DDK Period (DDK Rhythm);

            Norm: 5.8% (disordered voices have a higher variation)

DDKjit:  Pertubation of the DDK period; norm: 1.002% - 1.161% (disordered high variation)

Frequency and Intensity: task “read MY GRANDFATHER”

Frequency Range: norm: 22.7 semitones, (11-17 semitones is below normal)

Dynamic Range: minimum is 30 dB

Measures of Quality:

1.      Harmonics to noise ratio:  a measure of the proportion of harmonic sound to noise in the voice measured in decibels.   This measure can be useful form making objective quantitative assessments of breathiness, roughness, or hoarseness of a person’s voice. Averages around 15 dB.

2.      Voice tremor: refers to a regular variation the fundamental frequency or amplitude of the voice.  Usually the variation is about 3-5 Hz about the mean fundamental frequency. 

3.      Phonation time:

            Maximum Phonation time: The maximum time a subject can sustain a tone on one breath.  Norms: Adult males: 20 sec, females 15 sec.; children 10 seconds. Short maximum phonation times reflect inefficiency of the phonatory or respiratory system.

            S/Z ratio:  The maximum sustained phonation time of /s/ divided by the maximum sustained phonation time of /z/.  A normal speaker would be expected to sustain both the voiceless/s/ and the voiced /z/ for approximately equal durations, resulting in a ratio of 1. S/Z ratios greater than 1.4 indicate vocal fold pathology.

4.      Voice:

            Voice stoppages When silences become longer than normally expected or appear unexpectedly during phonation, they call attention to themselves, disrupt intelligibility and are considered abnormal.

            Frequency breaks: A shift in fundamental frequency either up or down in frequency.