Learning Objectives Describe how speakers control frequency and amplitude of vocal fold vibration Describe psychophysical attributes of pitch, loudness.
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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 (F 0 ) Control What factors dictate the vibratory frequency of the vocal folds? Anatomical factors Males ↑ VF mass and length = ↓ F o Females ↓ VF mass and length = ↑ F o Subglottal pressure adjustment – show example ↑ P sg = ↑ F o Laryngeal and vocal fold adjustments ↑ CT activity = ↑ F o TA activity = ↑ F o or ↓ F o Extralaryngeal adjustments ↑ height of larynx = ↑ F o
Characterizing Fundamental Frequency (F 0 ) Average F 0 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: F 0 ↓ Older males: F 0 ↑ F 0 variability F 0 varies due to –Syllabic & emphatic stress –Syntactic and semantic factors –Phonetics factors (in some languages) Provides a melody (prosody) Measures –F 0 Standard deviation ~2-4 semitones for normal speakers –F 0 Range maximum F 0 – minimum F 0 within a speaking task
Estimating the limits of vocal fold vibration Maximum Phonational Frequency Range highest possible F 0 - lowest possible F 0 Not a speech measure measured in Hz, semitones or octaves Males~ 80-700 Hz 1 Females~135-1000 Hz 1 Around a 3 octave range is often considered “normal” 1 Baken (1987)
Approaches to Measuring Fundamental Frequency (F 0 ) Time domain vs. frequency domain Manual vs. automated measurement Specific Approaches Peak picking Zero crossing Autocorrelation The cepstrum & cepstral analysis
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? Time Sound Pressure Frequency Amplitude Time Domain (waveform) Frequency Domain (amplitude spectrum) Fourier Transform
What is a cepstrum? Frequency Amplitude 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/m 2 Intensity is proportionate to Pressure 2
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 = 10 1 = 10 x 1 100 = 10 2 = 10 x 10 1000= 10 3 = 10 x 10 x 10 0.1 = 10 -1 = 1/10 x 1 Logarithmic scales use the exponents for the number scale log 10 10 = 1 log 10 100 = 2 log 10 1000=3 log 10 0.1 = -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/m 2 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 (I m / I r ) I m –measured intensity I r – reference intensity A bel is pretty big, so we tend to use decibel where deci is 1/10. So 10 decibels makes one bel dB IL = 10log 10 (I m / I r )
Intensity vs. Pressure Intensity is trickier to measure. Pressure is easy to measure – a microphone is a pressure measuring device. Intensity is proportionate to Pressure 2
Extending the formula to pressure Using some logrithmic tricks, this translates our equation for the decibel to dB SPL = (2)(10)log 10 (P m / P r ) = 20log 10 (P m / P r )
Amplitude control during speech Subglottal pressure adjustment ↑ P sg = ↑ 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 dB SPL SPL Variability SPL to mark stress Contributes to prosody Measure –Standard deviation for neutral reading material: ~ 10 dB SPL
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?
Breathiness Perceptual 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’ Frequency Amplitude Harmonic peak
From Hillenbrand et al. (1996) First harmonic amplitude
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
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