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Adler Assignment Sources, Vowel/Timbre, Role of listener perception,…
Adler Assignment Sources
Hixon
Important Passages
The acoustic theory of vowel production can be stated in very broad terms, as follows: for vowel production, the vocal tract resonates like a tube closed at one end, and shapes an input signal generated by the vibrating vocal folds. 289
That speech signal represents the blending of the input and filter characteristics. Because of this blending, the output signal cannot reveal the exact characteristics of the input (source) signal unless the output signal is separated into its source and filter parts. 292
The more rapidly the vocal folds come together, the steeper the closing part of the Vg [glottal flow] signal. 292
The ratio of open time to closed time for each cycle...may be an important determinant of how much of the source signal is periodic and how much is aperiodic. This is important when considering the physiological and acoustical basis of pathological voice quality. 292
The important features of this spectrum are: (a) the series of frequency components at consecutive-integer multiples of the lowest-frequency component; and (b) the relative amplitudes of the frequency components that decrease systematically as frequency increases. This is the glottal source spectrum. 293
There is a systematic relationship between this closing slope and the "tilt" of the glottal spectrum: the steeper the closing slope in the Vg waveform (the faster the vocal folds return to the midline on each cycle), the less tilted the glottal spectrum. 295
...the input signal generated by the vibrating vocal folds is a complex periodic waveform whose spectrum consists of a consecutive integer series of harmonics at whole-number multiples of the F0. The harmonics in the glottal spectrum systematically decrease in relative amplitude with increasing frequency. 297
Because the excitation occurs when the folds approximate and the oral end of the vocal tract is open for vowel production, the vocal tract resonates like a tube closed at one end. 298
...to say that the vocal tract resonances are excited each time the vibrating vocal folds snap together...[means that] a waveform is initiated each time the vocal folds snap together... waveforms are initiated for each resonant frequency of the tube. 298-9
If the mass and compliance characteristics of the vocal tract tube can be determined, the resonance curve for the tube can be constructed. Because the vocal tract resonates like a tube, there are multiple peaks (ie. resonances) along the resonance curve, each with its own bandwidth. 302
...the first three peaks in a vowel spectrum [F-pattern] have great importance for the acoustic and perceptual specification of vowel identity. 307
When a formant frequency is close to the resonant frequency of a structure such as the cheek, the tissue will absorb some of the energy and transform it into its own vibratory event. This absorption of acoustic energy by vocal tract structures is another form of energy loss and contributes to the damping of vocal tract resonances. 307
Chen
Important Passages
An essential feature of human voice is that the pitch frequency, defined as the inverse of the pitch period, is constantly varying. 130
...it is apparent that although the pitch period changes by a factor of two, the underlying elementary waveforms representing the color of a vowel are essentially identical. 135
...it is clear that for each pitch period, the signal starts with a strong impulse, then decays. The high-frequency components...decay faster...The medium...more slowly...[and] The low-frequency components...even more slowly. 135
The entire signal can be constructed by the superposition principle, which...states that the response caused by two or more stimuli is the sum of the responses caused by each stimulus individually. 136
...for each pitch period, the signal starts with a strong impulse, then decays. For each vowel, the underlying elementary waveforms are essentially identical. 135
...for each pitch period, the signal starts with a strong impulse, then decays. 135
Plomp Intelligent Ear
Important Passages
The ear distinguishes between frequency components originating from different sound sources, as opposed to components from the same source...auditory perception involves synthesis as well as analysis. 12
[referring to the voice] The duration of each period of [air pressure] vibration determines the pitch of the sound, whereas waveform characteristics determine its timbre. The ear is able to process sounds in such a way that both pitch and timbre of each individual sound are traced. This implies that the ear separates, in one way or another, these sounds in terms of their period duration as well as their waveform. 13
The first analyzing stage...is realized in the cochlea by means of a hydromechanical system that analyzes the incoming sound into sinusoidal components. 13
...the ear, on the one hand, can separate sinusoids originating from different sources, yet on the other, works to blend into a single percept the harmonics of the same tone. 18
...although the ear analyzes sounds in terms of their sinusoidal components, the harmonics of a tone are (normally) not heard individually but fuse into a single percept, with features of pitch, loudness, and timbre. 19
...a waveform is determined not only by the amplitudes of the sinusoidal components but also by their phases, that is, differences in the timing of the components. 19
...the ear's frequency-analyzing power is limited to sinusoidal components differing by more than about 20%, corresponding with slightly less than 1/3 octave [critical band of hearing]. Only the first five harmonics of a tone are distinguishable, whereas the higher ones are not. Therefore, it seems reasonable that a spectral analysis with 1/3-octave band filters is sufficient to describe the perceptually relevant differences in the tone's sound spectrum. 20
...there is a close relation between spectral differences for vowels measured in 1/3 octaves and perceptual differences as judged by listeners. 22
Vowels are excellent examples for demonstrating the different origins of the percepts of pitch and timbre. These two attributes of tones are essentially independent of each other. Any vowel can be spoken or sung at different pitches and yet preserves its characteristic timbre, remaining identifiable as the same vowel. 23
...pitch and timbre are not entirely unrelated. For the extreme case of a sinusoidal tone without harmonics, the tone's frequency as its single variable determines pitch as well as timbre, with the consequence that low-pitched sinusoidal tones are described as "dull" and high-pitched tones as "sharp." 24
It is a general rule that the overall slope of a sound's spectrum is the main determinant of its perceived timbre, varying from dull (strong fundamental) to sharp (strong higher harmonics). 24
[referring to the voice] The duration of each period of [air pressure] vibration determines the pitch of the sound, whereas waveform characteristics determine its timbre. The ear is able to process sounds in such a way that both pitch and timbre of each individual sound are traced. This implies that the ear separates, in one way or another, these sounds in terms of their period duration as well as their waveform. 13
Plomp Tone Perception
Important Passages
The hypothesis that the pitch of a tone is based on the period of the sound waves may be criticized on the ground that this periodicity is preserved up to 3000-4000 cps [cycles per second], whereas we are able to distinguish tones up to about 16000 cps. This is one of the most serious arguments against periodicity pitch. It is obviated by Wever's assumption...that the ear is provided with two pitch-detecting mechanisms: one, based on periodicity, for low frequencies and one, based on place of maximal stimulation along the basilar membrane, for high frequencies. 130
Traditionally, the timbre of complex tones is considered as depending upon the relative amplitudes of the harmonics...in practice, we don't hear the pitches of the harmonics individually but the presence of the harmonics is manifested implicitly by the way in which they affect timbre as an attribute of the tone as a whole. 131
Hypothesis V. The distribution of stimulation along the basilar membrane determines timbre. ...The fact that, in whispering, the vowels are even recognized when the voice tract is stimulated by wide-band noise instead of periodic waves supports the view that the stimulation pattern along the basilar membrane as the physiological correlate of frequency spectrum must be considered as the basis of timbre. 131
...in addition to pitch, simple tones have timbre... [and] some resemblance, depending upon frequency, with particular speech vowels... It is plain that this resemblance is related to the location of the formants in the frequency range. 132
As a name for this attribute of simple tones [timbre], the term brightness...appears to be the most appropriate one...pitch is correlated with periodicity and brightness with frequency. 132
If timbre has to be defined as the sum of all aspects left when loudness and pitch are "subtracted" from the total sensation of a sound, then this definition includes much more than has been considered above. It is justified, however, to consider frequency spectrum as the main component of timbre in its wide interpretation. 133
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