Learning Objectives

• Describe how speakers control frequency and amplitude of vocal fold vibration

• Describe psychophysical attributes of pitch, loudness and quality in physiological and acoustic terms

• Define terms such as speaking fundamental frequency, speaking fundamental frequency variability, harmonics (or signal) to noise ratio, jitter, shimmer, cepstrum, quefrency, and rahmonic amplitude

What is the difference between pitch and frequency?

Quantifying frequency

• Hertz: cycles per second (Hz)

Non-linear scales

• Octave scale– 1/3 octave bands– Semitones– Cents

• Other “auditory scales”: e.g. mel, phon

Fundamental Frequency (F0)Control

What factors dictate the vibratory frequency of the vocal folds?

• Anatomical factorsMales ↑ VF mass and length = ↓ Fo

Females ↓ VF mass and length = ↑ Fo

• Subglottal pressure adjustment – show example↑ Psg = ↑ Fo

• Laryngeal and vocal fold adjustments↑ CT activity = ↑ Fo

TA activity = ↑ Fo or ↓ Fo

• Extralaryngeal adjustments↑ height of larynx = ↑ Fo

Characterizing Fundamental Frequency (F0)

Average F0

• speaking fundamental frequency (SFF)

• Correlate of pitch

• Infants– ~350-500 Hz

• Boys & girls (3-10) – ~ 270-300 Hz

• Young adult females– ~ 220 Hz

• Young adult males– ~ 120 Hz

Older females: F0 ↓

Older males: F0 ↑

F0 variability• F0 varies due to

– Syllabic & emphatic stress– Syntactic and semantic factors– Phonetics factors (in some

languages) • Provides a melody (prosody)

• Measures– F0 Standard deviation

• ~2-4 semitones for normal speakers– F0 Range

• maximum F0 – minimum F0 within a speaking task

Estimating the limits of vocal fold vibration

Maximum Phonational Frequency Range

• highest possible F0 - lowest possible F0

• Not a speech measure• measured in Hz, semitones or octaves• Males ~ 80-700 Hz1

• Females ~135-1000 Hz1

• Around a 3 octave range is often considered “normal”

1Baken (1987)

Approaches to Measuring Fundamental Frequency (F0)

• Time domain vs. frequency domain

• Manual vs. automated measurement

• Specific Approaches• Peak picking• Zero crossing• Autocorrelation• The cepstrum & cepstral analysis

Autocorrelation

Data Correlation

+ 1.0

+ 0.1

- 0.82

+ 0.92

What is a cepstrum?

• A cepstrum involves performing a spectral analysis of an amplitude spectrum

• Returns sound representation to a “time-like” domain analysis: quefrency-domain

• Location of the dominant energy in the cepstrum is typically associated with the fundamental frequency of the signal

What is a cepstrum?

TimeSou

nd P

ress

ure

Frequency

Am

plitu

de

Time Domain (waveform)

Frequency Domain (amplitude spectrum)

Fourier Transform

What is a cepstrum?

Frequency

Am

plitu

de

Frequency Domain (amplitude spectrum)

What is a cepstrum?

Fourier Transform (number 2)

Quefrency (msec)

Dominant rahmonic-quefrency location: fundamental period-height: degree of periodicity

Learning Objectives

• Describe how speakers control frequency and amplitude of vocal fold vibration

• Describe psychophysical attributes of pitch, loudness and quality in physiological and acoustic terms

• Explain what the decibel is and why it is a preferred way to quantify amplitude

What is the difference between amplitude and loudness?

Quantifying amplitude

Sound pressure level • Pressure = force/area• Units: micropascals

Sound intensity• Intensity = Power/area where

– power=work/time– work=force*distance

• Units: watts/m2

Intensity is proportionate to Pressure2

What is the decibel scale?

• We prefer to use the decibel scale to represent signal amplitude

• We are used to using measurement scales that are absolute and linear

• The decibel scale is relative and logarithmic

Linear vs. logarithmic• Linear scale: 1,2,3…

• For example, the difference between 2 and 4 is the same as the difference between 8 and 10.

• We say these are additive

18

Linear vs. logarithmic• Logarithmic scales are multiplicative• Recall from high school math and hearing science

10 = 101 = 10 x 1100 = 102 = 10 x 101000= 103 = 10 x 10 x 100.1 = 10-1 = 1/10 x 1

Logarithmic scales use the exponents for the number scale

log1010 = 1

log10100 = 2

log 101000=3

log 100.1 = -1

Logarithmic Scale

• base doesn’t have to be 10

• In computer science, base = 2

• In the natural sciences, the base is often 2.7… or e

Logarithmic Scale

• Why use such a complicated scale?– logarithmic scale squeezes a very wide range

of magnitudes into a relatively compact scale– this is roughly how our hearing works in that a

logarithmic scales matches our perception of loudness change

Absolute vs. relative measurement

• Relative measures are a ratio of a measure to some reference

• Relative scales can be referenced to anything you want.

• decibel scale doesn’t measure amplitude (intensity or pressure) absolutely, but as a ratio of some reference value.

Typical reference values

• Intensity– 10-12 watts/m2

• Sound Pressure Level (SPL) – 20 micropascals

Why do we use these particular values?

However…

• You can reference intensity/pressure to anything you want

For example,

• Post therapy to pre therapy

• Sick people to healthy people

• Sound A to sound B

Now, let us combine the idea of logarithmic and relative…

bel= log 10(Im/ Ir)

Im –measured intensity

Ir – reference intensity

A bel is pretty big, so we tend to use decibel where deci is 1/10. So 10 decibels makes one bel

dBIL = 10log 10(Im/ Ir)

Intensity vs. Pressure

• Intensity is trickier to measure.

• Pressure is easy to measure – a microphone is a pressure measuring device.

• Intensity is proportionate to Pressure2

Extending the formula to pressure

Using some logrithmic tricks, this translates our equation for the decibel to

dBSPL= (2)(10)log 10(Pm/ Pr) = 20log 10(Pm/ Pr)

Amplitude control during speech

• Subglottal pressure adjustment↑ Psg = ↑ sound pressure

• Laryngeal and vocal fold adjustments↑ medial compression = ↑ sound pressure

• Supralaryngeal adjustments– Optimizing sound radiation from vocal tract

Sound Pressure Level (SPL)

Average SPL• Correlate of loudness• conversation:

• ~ 65-80 dBSPL

SPL Variability SPL to mark stress• Contributes to prosody• Measure

– Standard deviation for neutral reading material:

• ~ 10 dBSPL

Estimating the limits of sound pressure generation

Dynamic Range

• Amplitude analogue to maximum phonational frequency range

• ~50 – 115 dB SPL

Learning Objectives

• Describe psychophysical attributes of pitch, loudness and quality in physiological and acoustic terms

• Define terms such as speaking fundamental frequency, speaking fundamental frequency variability, harmonics (or signal) to noise ratio, jitter, shimmer, cepstrum, quefrency, and rahmonic amplitude

Vocal Quality

• no clear acoustic correlates like pitch and loudness

• However, terms have invaded our vocabulary that suggest distinct categories of voice quality

Common Terms• Breathy• Tense/strained• Rough• Hoarse

Are there features in the acoustic signal that correlate with these

quality descriptors?

BreathinessPerceptual Description• Audible air escape in the voice

Physiologic Factors• Diminished or absent closed phase• Increased airflow

Potential Acoustic Consequences• Change in harmonic (periodic) energy

– Sharper harmonic roll off• Change in aperiodic energy

– Increased level of aperiodic energy (i.e. noise), particularly in the high frequencies

harmonics (signal)-to-noise-ratio (SNR/HNR)

• harmonic/noise amplitude HNR

– Relatively more signal– Indicative of a normality

HNR– Relatively more noise– Indicative of disorder

• Normative values depend on method of calculation

• “normal” HNR ~ 15

Harmonic peak

Noise ‘floor’

Noise ‘floor’

Frequency

Am

plitude

Harmonic peak

From Hillenbrand et al. (1996)

First harmonic amplitude

Prominent Cepstral Peak

Spectral Tilt: Voice Source

Spectral Tilt: Radiated Sound

Peak/average amplitude ratio

From Hillenbrand et al. (1996)

WMU Graduate Students

Tense/Pressed/Effortful/Strained Voice

Perceptual Description• Sense of effort in production

Physiologic Factors• Longer closed phase• Reduced airflow

Potential Acoustic consequences• Change in harmonic (periodic) energy

– Flatter harmonic roll off

Pressed

Breathy

Spectral Tilt

Acoustic Basis of Vocal Effort

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effort

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200.000000

300.000000

400.000000

500.000000

Reg

ress

ion

Ad

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Pre

ss)

Pre

dic

ted

V

alu

eDependent Variable: effort

Scatterplot

F0 + RMS + Open Quotient

Perc

epti

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f E

ffor

t

Tasko, Parker & Hillenbrand (2008)

Roughness

• Perceptual Description– Perceived cycle-to-cycle variability in voice

• Physiologic Factors– Vocal folds vibrate, but in an irregular way

• Potential Acoustic Consequences– Cycle-to-cycle variations F0 and amplitude– Elevated jitter– Elevated shimmer

Period/frequency & amplitude variability

• Jitter: variability in the period of each successive cycle of vibration

• Shimmer: variability in the amplitude of each successive cycle of vibration

…

Jitter and Shimmer

Sources of jitter and shimmer• Small structural asymmetries

of vocal folds• “material” on the vocal folds

(e.g. mucus)• Biomechanical events, such as

raising/lowering the larynx in the neck

• Small variations in tracheal pressures

• “Bodily” events – system noise

Measuring jitter and shimmer• Variability in measurement

approaches• Variability in how measures are

reported• Jitter

– Typically reported as % or msec– Normal ~ 0.2 - 1%

• Shimmer– Can be % or dB– Norms not well established