Content uploaded by Jody Kreiman
Author content
All content in this area was uploaded by Jody Kreiman on Aug 21, 2015
Content may be subject to copyright.
Acoustic properties of different kinds of creaky voice
Patricia Keating1, Marc Garellek2, Jody Kreiman3
1Dept. Linguistics, UCLA, Los Angeles CA USA 90095; 2Dept. Linguistics, UCSD, San Diego CA USA 92093,
3Dept. Head & Neck Surgery, UCLA, Los Angeles CA USA 90095
keating@humnet.ucla.edu; mgarellek@ucsd.edu; jkreiman@ucla.edu
ABSTRACT
There is not one kind, but instead several kinds, of
creaky voice, or creak. There is no single defining
property shared by all kinds. Instead, each kind
exhibits some properties but not others. Therefore
different acoustic measures characterize different
kinds of creak. This paper describes how various
acoustic measures should pattern for each kind of
creak.
Keywords: phonation, voice quality, creaky voice
1. INTRODUCTION
The term “creaky voice” (or “creak”, used here
interchangeably) refers to a number of different
kinds of voice production. Early linguistic
descriptions of creak (e.g. Laver [32]) enumerated
many characteristics: low subglottal pressure and
glottal flow, slack, thick, compressed vocal folds
with a short vibrating length, ventricular contact
with the folds, weak or damped pulses, low F0,
irregular F0, period-doubled vibration. Later
descriptions (e.g. [7, 20, 28]) added such properties
as irregular amplitude, low Open Quotient, skewed
glottal pulses, narrow formant bandwidths and sharp
harmonics, abrupt closure of the folds, and low
spectral tilt. Yet it seems clear that these
characteristics are not all seen in each instance of
creak, and that (when the full range of types is
considered) there is no single defining characteristic
shared by all instances.
Indeed, previous studies have argued that there
are specific sub-categories of creak, each with its
own set of characteristics. Hedelin and Huber [24]
distinguished “creak” (or “fry” or “pulse”, with low
F0 and strong damping), “creaky voice” (with
irregular pulses), and “diplophonia” (with period
doubling). Batliner et al. [5] used six acoustic
properties to distinguish five different types of
“laryngealization”, but their brief report provides
little discussion. Later, a pair of papers from
presentations at the 1999 ICPhS proposed similar
categories, based primarily on visual inspection of
acoustic displays. First, Gerratt and Kreiman [20]
described two “supraperiodic” types - one “period
doubled” (with interharmonics), and one with
“amplitude modulation” - plus a highly aperiodic
“noisy” type. They demonstrated that these three
types are perceptually distinct to ordinary listeners.
They also described “vocal fry”, with visibly
damped pulses. Second, Redi and Shattuck-
Hufnagel [35] distinguished four types of creaky
voice: irregular “aperiodicity”, damped, low-F0
“creak”, “diplophonia” (with any kind of alternating
pulse frequency, amplitude, or shape), and the rare
“squeak” (with a sudden sustained high F0). Redi
and Shattuck-Hufnagel showed that not only do
these types vary across speakers, but also across
positions-in-utterance for individual speakers.
In this paper we build on these previous studies
about different kinds of creak from the perspective
of researchers performing varied acoustic analyses
of a range of voice samples. If each acoustic
measure reflects a specific aspect of creak, and if
different kinds of creak exhibit specific
combinations of these aspects, then different kinds
of creak will be distinguished from modal voice by
distinct acoustic measures. Specifically, we attempt
to relate different kinds of creak to acoustic
measures already used by researchers.
2. PROTOTYPICAL CREAKY VOICE
We begin by describing what we take to be
prototypical creaky voice, in line with the brief
definitions given in many research papers.
Prototypical creaky voice has the following three
key properties: (1) low rate of vocal fold vibration
(F0), (2) irregular F0, and (3) constricted glottis: a
small peak glottal opening, long closed phase, and
low glottal airflow.
Figure 1: Waveform showing prototypical creak,
phrase-final by a male English speaker, vowel /e/.
Fig. 1 shows a sample waveform of creaky voice
with these properties, from a male speaker of
English. F0 is in the range of 70 Hz, but irregular.
Glottal constriction is inferred from a high Contact
Quotient in the simultaneous EGG signal.
3. OTHER KINDS OF CREAKY VOICE
While prototypical creaky voice is often encountered
in speech samples, much of what is called creaky
voice – indeed, is perceived as creaky voice – may
differ from this prototype in one or more ways. Each
of the three properties of prototypical creak can be
lacking, yielding several further kinds of creak.
3.1. Vocal fry
Although the term “vocal fry” is often used
interchangeably with “creak”, vocal fry differs from
prototypical creak in a major way: the glottis is
constricted and F0 is low, but it is not necessarily
irregular. Indeed it is often quite periodic, as in Fig.
2. Its special property is high damping of the pulses
– this property, due in part to the low F0, makes
individual pulses distinct and separately audible (the
“picket fence” effect). Thus the prototypical low-F0
property is enhanced.
Figure 2: Waveform showing phrase-final vocal
fry by a female English speaker, with regular F0.
It has been suggested that ventricular incursion,
as observed by [1], can be one contributor to vocal
fry (though cf. [11]): the ventricular folds contact
and mechanically load the vocal folds. This
increases the effective mass of the folds, so F0 is
extremely low; it can also make vibration irregular.
However, as vocal fry was the only kind of creak
examined by [1], the incidence of ventricular
involvement across kinds of creak is not known.
3.2. Multiply pulsed voice
A very common form of creak involves a special
kind of F0 irregularity: alternating longer and shorter
pulses. (See [20] for a literature review.) In the case
of double pulsing (or period doubling), there are two
simultaneous periodicities; higher multiples are also
possible. There are thus multiple F0s, usually one
quite low and another about (though not exactly) an
octave higher, but the resulting percept is usually of
an indeterminate pitch, plus roughness. Thus the
prototypical low-F0 is not necessarily present.
These pulses generally have a very long closed
phase, as shown by [41]’s imaging of glottal areas in
double- and triple-pulsed creak. See Figs. 3 and 4 for
sample waveform and spectrum, the latter showing
two sets of harmonics.
Figure 3: Waveform showing double pulsing by a
male English speaker on a steady /a/. Note the
regular alternation of strong and weak pulses.
Figure 4: Spectrum of vowel in Fig. 3. Note two
sets of harmonics.
3.3. Aperiodic voice
Another variant of F0 irregularity is when it is taken
to the extreme – vocal fold vibration is so irregular
that there is no periodicity and thus no perceived
pitch. See Fig. 5. Like multiply pulsed voice,
aperiodic voice lacks the prototypical property of
low F0; instead, the property of irregular F0 is
enhanced, and the voice is therefore noisy.
Figure 5: Waveform showing extreme
aperiodicity, phrase-finally by a female English
speaker.
3.4. Nonconstricted creak
This is a voice quality described by Slifka [38, 39].
F0 is low and irregular, as in prototypical creak; but
the glottis is spreading, not constricted, and therefore
airflow through the glottis is higher, not lower. This
kind of creak is attested utterance-finally, with the
vocal folds beginning to spread before the utterance
is over. The naturally-low subglottal pressure in this
position, combined with the spreading glottis, means
that conditions for sustaining voicing are not ideal.
The slow and irregular vibrations indicate voicing at
the edge of failing. See Fig. 6.
While this kind of creak, with its increasing
airflow, is necessarily somewhat breathy, it differs
from Laver’s [32] proposed “breathy creak”, said to
involve airflow through a posterior (arytenoid)
glottal gap, simultaneous with anterior creak.
Figure 6: Waveform showing nonconstricted
creak, phrase-final by a male English speaker. The
Contact Quotient from EGG is low in this token,
indicating little glottal constriction.
3.5. Tense/pressed voice
When the glottis is constricted, but the F0 is neither
low nor irregular, a tense or pressed voice quality is
heard. While not always considered a form of creaky
voice, it can function phonologically as such in
languages in which a creaky (or laryngealized)
phonation can co-occur with high tone. Here the
constricted glottis is criterial. See Fig. 7.
The discussion above is summarized in Table 1.
Figure 7: Waveform, spectrogram, and pitch track
of “creaky” voice with high tone in Mazatec –
phonetically a tense or pressed voice quality.
Reduced amplitude may be due to constricted
glottis.
4. ACOUSTIC MEASURES OF PROPERTIES
OF CREAK
These will be considered primarily with reference to
the measures provided by our program VoiceSauce
([36, 37]), freely available and often used to study
phonation types in languages. In a few cases,
exploratory re-synthesis using the UCLA Voice
Synthesizer (e.g. [29]) has been compared. The five
properties listed in Table 1 are discussed in turn.
Table 1: Properties characterizing different kinds
of creak. Check mark means a property
characterizes a type; NO means it does not; blank
means variable or unknown.
Property
>
low
F0
irreg
F0
glottal
constr
damped
pulses
sub-
harms
Main
correlate
>
Type ˅
low
F0
high
noise
low
H1-
H2
low
noise;
narrow
BWs
high
SHR
proto-
typical
√
√
√
vocal fry
√
√
√
multiply
pulsed
√
√
√
aperiodic
NO
√
√
noncon-
stricted
√
√
NO
tense
NO
√
4.1. Low F0
Creaky voice usually has lower F0 than modal voice.
Low F0 has been shown to be a key correlate of
creaky voice in Hmong [13] and Mixtec [18]. Yet F0
can be difficult to estimate when irregular;
sometimes no F0 can be found. The STRAIGHT
pitchtracker [27] is fairly robust in the face of F0
irregularity. Another option, especially appropriate
for multiply-pulsed creak, is Sun’s method [40],
based on his Subharmonic-to-Harmonic ratio
measure (SHR, see below). This is specifically
designed to estimate a perceptual F0 in the face of
competing simultaneous harmonics. See also [24]
for additional discussion of methods for tracking
irregular F0. In the limit, if no F0 can be extracted,
the voice is aperiodic, and thus without the low-F0
property. Our re-synthesis also suggests that
lowering the F0 lowers Cepstral Peak Prominence, a
measure of noise (see 4.2).
4.2. Irregular F0
Creaky voice usually has less regular voicing
than modal voice. This variability can be measured
as pulse-to-pulse jitter, or as the standard deviation
of the F0, or by autocorrelation [2]. But such voicing
irregularity is perceived as noise, not distinct from
other kinds of noise [29]. Therefore irregular F0 can
be measured as spectral noise, by e.g. Harmonic-to-
Noise Ratios (HNR) across different frequency
bands, by [8]’s method, or normalized as in [25].
Low HNR values indicate less strong periodic
excitation relative to glottal noise – due either to ill-
defined harmonics (as with irregular F0) or
prominent glottal noise (as with nonconstricted
creak). Note, however, that vocal fry will have a
relatively high HNR, since in fry the glottal pulses
are so sharply defined.
Irregular F0 via low HNR is a correlate of creaky
voice in Ju|’hoansi [33], Mazatec [16], Hmong [13],
English [13,14,15], and Taiwanese [34]. Our re-
synthesis suggests that adding jitter lowers the
Cepstral Peak Prominence (i.e., increases noise), but
also the amplitude of the higher formants (i.e.,
increases spectral tilt).
4.3. Constricted glottis
The most common measure of creak is the amplitude
difference between the first and second harmonics,
H1-H2 - see e.g. [21]. (This is best estimated by the
formant-corrected version H1*-H2*, as in [22],
[26]). This measure generally reflects glottal
constriction, with a lower value indicating greater
constriction. [30] used high-speed imaging of the
glottis to show that as long as there is no posterior
glottal gap, H1-H2 is usually closely related to the
glottal Open Quotient. And, [14] and others have
found that it is well correlated with Contact Quotient
measures from electroglottography. Creaky voice
generally has low values of H1-H2, because the
glottis is usually constricted. But in non-constricted
creak, H1-H2 will have higher, not lower, values
than modal voice.
Low H1-H2 has been shown to be a correlate of
creaky voice in Zapotec [4, 12], Ju|’hoansi [33],
Mazatec [6, 16], Hmong [3, 13], English [15],
Trique [10], Taiwanese [34], and of constricted tense
voice in Mpi [6], Chong [9] and Yi languages [31].
Constricted glottis may give rise to vibrations that
impart more energy to higher-frequency harmonics,
perhaps through a more abrupt closure [23]. At the
same time, low flow through the glottis means less
energy in H1. As a result, various measures of
harmonic amplitude differences generally have
lower values in creak (i.e., less spectral tilt). Such
results have been found for Mazatec [6, 16], English
[15], Zapotec [4], and Trique [10]. Our re-synthesis
suggests that a smaller H1-H2 also increases HNR
measures (i.e., lowers noise). However, none of
these are measures of constricted glottis per se.
4.4. Damping
Damping of glottal pulses plays out in two kinds of
measures. First, as noted in 4.2 above: unless the F0
is very irregular, the harmonics in damped pulses
should be well defined, such that harmonic-to-noise
ratios should be high. Second, due to the long closed
phase, formant bandwidths should be narrow (e.g.
low B1 values). We have so far been unable to
demonstrate this through re-synthesis, however.
4.5. Subharmonics in multiple pulsing
As already noted, multiply-pulsed creak has multiple
sets of harmonics. Generally one set is stronger and
dominates the harmonic spectrum, while the other
harmonics (“subharmonics” or “interharmonics”)
appear between these stronger ones. Sun’s
Subharmonic-to-Harmonic Ratio SHR [40]
measures the relative strengths of the two sets, and
has been used by Sun to characterize the strength of
period doubling. Multiply-pulsed creak will have
more subharmonics, so higher SHR values [17].
5. CONCLUSION
Prototypical creaky voice can be distinguished
acoustically by its lower F0, by its irregular F0
(which results in lower values of various harmonic-
to-noise measures), and by its lower H1 and H1-H2,
and other harmonic difference measures. Just one or
two of these prototypical properties apparently
suffices to make a sample creaky. Creak that is vocal
fry with a regular F0 could instead show higher
HNR together with lower formant bandwidths.
Creak that is multiply pulsed can lack a clear F0 but
instead show subharmonics (resulting in higher
values of SHR). Non-constricted creak can instead
show higher H1-H2, but still with a low and
irregular F0. Creak that is more like tense or pressed
voice can have a mid or high, and regular, F0.
We hope to convey that there is no
straightforward answer to the FAQ, “What is the
best acoustic measure for creaky voice?”. It entirely
depends on what kind(s) of creak the investigator
wants to identify. It cannot be expected that
measures such as H1*-H2*, or jitter, etc., will
always characterize creaky voice, since there are
special sub-types that are not glottally constricted, or
not irregular, etc. It is crucial to keep in mind that
when different acoustic measures seem to “disagree”
about the creakiness of a speech sample, the set of
measures as a whole is in fact giving valuable
information about the specific voice quality in the
sample.
6. ACKNOWLEDGMENTS
We thank NSF grants BCS-0720304 and IIS-
1018863, and NIH grant DC01797, for funding.
7. REFERENCES
[1] Allen, E., Hollein, H. 1973. A laminagraphic study of
pulse (vocal fry) phonation. Folia Phon. 25, 241-250.
[2] Ashby, M., Przedlacka, J. 2014. Measuring
incompleteness: Acoustic correlates of glottal
articulation. JIPA 44, 283-296.
[3] Andruski, J. 2006. Tone clarity in mixed
pitch/phonation-type tones. J. Phonetics 34, 388-404.
[4] Avelino, H. 2010. Acoustic and electroglottographic
analyses of nonpathological, nonmodal phonation. J.
Voice 24, 270-280.
[5] Batliner, A., Berger, S., Johne, B., Kießling, A. 1993.
MÜSLI: A classification scheme for laryngealizations.
Proc. ESCA Workshop on Prosody, Lund, 176-179.
[6] Blankenship, B. 2002. The timing of nonmodal
phonation in vowels. J. Phonetics 30, 163-91.
[7] Childers, D.G., Lee, C.K. 1991. Vocal quality factors:
Analysis, synthesis, and perception. J. Acoust. Soc.
Am. 90, 2394-2410.
[8] de Krom, G. 1993. A cepstrum-based technique for
determining a harmonic-to-noise ratio in speech
signals. J. Sp. Hear. Res. 36, 254-66.
[9] DiCanio, C. 2009. The phonetics of register in
Takhian Thong Chong. JIPA 39, 162–188.
[10] DiCanio, C. 2012. Coarticulation between tone and
glottal consonants in Itunyoso Trique. J. Phonetics 40,
162-176.
[11] Edmondson, J.A, Esling, J. H. 2006. The valves of
the throat and their functioning in tone, vocal register
and stress: laryngoscopic case studies. Phonology 23,
157-191.
[12] Esposito, C. 2010. Variation in contrastive phonation
in Santa Ana Del Valle Zapotec. JIPA 40, 181-198.
[13] Garellek, M. 2012. The timing and sequencing of
coarticulated non-modal phonation in English and
White Hmong. J. Phonetics 40, 152-161.
[14] Garellek, M. 2014. Voice quality strengthening and
glottalization. J. Phonetics 45, 106-113.
[15] Garellek, M. (2015). Perception of glottalization and
phrase-final creak. J. Acoust. Soc. Am. 137, 822-831.
[16] Garellek, M., Keating, P. 2011. The acoustic
consequences of phonation and tone interactions in
Mazatec. JIPA 41, 185-205.
[17] Garellek, M., Keating, P. 2015. Phrase-final creak:
Articulation, acoustics, and distribution. Annual
Meeting of the Linguistic Society of America,
Portland, OR.
[18] Gerfen, C., Baker, K. 2005. The production and
perception of laryngealized vowels in Coatzospan
Mixtec. J. Phonetics 33, 311-334.
[19] Gerratt, B.R., Kreiman, J. 2001. Toward a taxonomy
of nonmodal phonation. J. Phonetics 29, 365-381.
[20] Gobl, C., Ní Chasaide, A. 2010. Voice source
variation and its communicative functions. In:
Hardcastle, W., Laver, J., Gibbon, F. (eds), The
Handbook of Phonetic Sciences (Second Edition).
Oxford: Blackwell, 378-423.
[21] Gordon, M., Ladefoged, P. 2001. Phonation types: A
cross-linguistic overview. J. Phonetics 29, 383-406.
[22] Hanson, H. M. 1995. Glottal characteristics of
female speakers. Ph.D. Dissertation, Harvard.
[23] Hanson, H. M, Stevens, K.N., Kuo, H.-K. J., Chen,
M.Y., Slifka, J. 2001. Towards models of phonation.
J. Phonetics 29, 451-480.
[24] Hedelin, P., Huber, D. 1990. Pitch period
determination of aperiodic speech signals. Proc.
ICASSP Albuquerque, 361-364.
[25] Hillenbrand, J., Cleveland, R., Erickson, R. 1994.
Acoustic correlates of breathy vocal quality. J. Sp.
Hear. Res. 37, 769-778.
[26] Iseli, M., Shue, Y.-L., Alwan, A. 2007. Age, sex, and
vowel dependencies of acoustic measures related to
the voice source. J. Acoust. Soc. Am. 121, 2283–2295.
[27] Kawahara, H., Katayose, H., de Cheveigné, A.,
Patterson, R. D. 1999. Fixed point analysis of
frequency to instantaneous frequency mapping for
accurate estimation of F0 and periodicity. Proc.
EUROSPEECH Budapest, 2781–2784.
[28] Klatt, D., Klatt, L. 1990. Analysis, synthesis, and
perception of voice quality variations among female
and male talkers. J. Acoust. Soc. Am. 87, 820-857.
[29] Kreiman, J., Gerratt, B.R. 2005. Perception of
aperiodicity in pathological voice. J. Acoust. Soc. Am.
117, 2201-2211.
[30] Kreiman J., Shue, Y.-L., Chen, G., Iseli, M., Gerratt,
B. R., Neubauer, J., Alwan, A. 2012. Variability in the
relationships among voice quality, harmonic
amplitudes, open quotient, and glottal area waveform
shape in sustained phonation. J. Acoust. Soc. Am. 132,
2625-2632.
[31] Kuang, J.J. 2013. Phonation in Tonal Contrasts.
Ph.D. dissertation, UCLA.
[32] Laver, J. 1980. The phonetic description of voice
quality. Cambridge: Cambridge University Press.
[33] Miller, A.L. 2007. Guttural vowels and guttural
coarticulation in Ju|’hoansi. J. Phonetics 35, 56-84.
[34] Pan, H., Chen, M., Lyu, S. 2011. Electroglottograph
and Acoustic Cues for Phonation Contrasts in Taiwan
Min Falling Tones. Proc. 12th INTERSPEECH
Firenze, 649-652.
[35] Redi, L., Shattuck-Hufnagel, S. 2001. Variation in
the realization of glottalization in normal speakers. J.
Phonetics 29, 407-429.
[36] Shue, Y.-L. 2010. The voice source in speech
production: Data, analysis and models. Ph.D.
Dissertation, UCLA.
[37] Shue, Y.-L., Keating, P., Vicenik, C., Yu, K. 2011.
VoiceSauce: A program for voice analysis. Proc. 17th
ICPhS Hong Kong, 1846-1849.
[38] Slifka, J. 2000. Respiratory constraints on speech
production at prosodic boundaries. Ph.D.
Dissertation, MIT.
[39] Slifka, J. 2006. Some physiological correlates to
regular and irregular phonation at the end of an
utterance. J. Voice 20, 171-186.
[40] Sun, X. 2002, Pitch determination and voice quality
analysis using Subharmonic-to-Harmonic Ratio. Proc.
ICASSP Orlando, 333-336.
[41] Whitehead, R. L., Metz, D. , Whitehead, B.H. 1984.
Vibratory patterns of the vocal folds during pulse
register phonation. J. Acoust. Soc. Am. 75, 1293-1297
