Acoustic, aerodynamic, physiologic, and perceptual properties of modal and vocal fry registers

Acoustic, aerodynamic, physiologic, and perceptual propertiesof modal and vocal fry registers

Michael Blomgren and Yang ChenDepartment of Communication Sciences, University of Connecticut, Storrs, Connecticut 06269-1085

Manwa L. NgDepartment of Speech Pathology and Audiology, Illinois State University, Normal, Illinois 61790

Harvey R. GilbertDepartment of Communication Sciences, University of Connecticut, Storrs, Connecticut 06269-1085

~Received 15 September 1997; accepted for publication 3 February 1998!

The purpose of the study was to examine the acoustic, aerodynamic, physiologic, and perceptualcharacteristics of modal and vocal fry production. Twenty normal speakers~10 males, 10 females!participated in the study. Speech material included four sustained vowels~/i/, /Ä/, /,/, /u/!, andsyllable strings of /pi/ repetitions produced in both modal and vocal fry registers. Acoustic data~fundamental frequency, jitter, shimmer, and signal-to-noise ratio!, aerodynamic data~airflow andair pressure!, and electroglottographic~EGG! data were obtained simultaneously. Resultsdemonstrated considerable differences across voice parameters for the modal and vocal fry registers.Fundamental frequency was significantly lower in vocal fry than in modal register for both malesand females, however, significant gender differences existed only in modal register. For both malesand females, measurements of jitter and shimmer were significantly higher and signal to noise ratiowas significantly lower in vocal fry. In addition, airflow rate in modal register was almost threetimes as high as the airflow rate in vocal fry register during sustained vowel production. Duringsyllable string production, subglottal air pressure values in modal register were approximately 1.5times higher than that in the vocal fry register. In general, these data emphasize that theaeromechanical mechanisms of vocal fold vibratory behavior are substantially different betweenmodal and vocal fry registers. A model of vocal fry phonation is presented to account for the presentresults. © 1998 Acoustical Society of America.@S0001-4966~98!04005-3#

PACS numbers: 43.70.Aj, 43.70.Gr, 43.75.Rs@AL #

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INTRODUCTION

According to Hollien~1974! there are three vocal registers. Although variously labeled over the past 40 years, cmon designations have included~a! falsetto or loft registerfor the highest of the human vocal frequencies,~b! modal orchest register for the ‘‘normal’’ speaking or singing voicand ~c! vocal fry, glottal fry, creak, or pulse register for thphonation produced at the lowest end of the human vofrequency range. Hollien stated that a vocal register is aries or range of consecutively phonated frequencies thatbe produced with nearly identical vocal quality and wlittle or no overlap in fundamental frequencies (F0) betweenadjacent registers. He suggested that a voice register caoperationally defined according to the following paramete~1! perceptual;~2! acoustic;~3! physiologic; and~4! aerody-namic. In addition, Daniloffet al. ~1980! reported that ‘‘thecomplex physiological structure of the larynx can vibratethree~or more! relatively different ways, giving rise to airflow modulation that yields acoustically and perceptuadistinct vocal quality’’ ~p. 209!. The present study explorethe acoustic, aerodynamic, physiologic, and perceptual cacteristics of two of the three normal voice registers; speccally, modal and vocal fry registers.

Modal register refers to the range ofF0 used in the‘‘normal mode’’ of speaking and singing~Hollien, 1974!.Vocal fry is a voice register approximately one octave bel

2649 J. Acoust. Soc. Am. 103 (5), Pt. 1, May 1998 0001-4966/98/10

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the frequencies noted for the normal male modal regisVocal fry consists of a train of discrete, low-frequency, glotal pulses produced by the larynx~Hollien and Wendahl,1968!. McGlone ~1967! indicated that vocal fry exists asphysiologically normal mode of laryngeal vibration whicresults in a distinctive acoustic signal.

A. Acoustic properties of vocal fry

The F0 ranges in modal register are characterizedvalues of approximately 100–140 Hz for males~Hollien andJackson, 1973; Krook, 1988!, and 175–240 for females~Sto-icheff, 1981; Krook, 1988!. In contrast, vocal fry is associated with a very lowF0 . The F0 of vocal fry samples ob-tained by Hollien and Wendahl~1968! ranged from 31.6 to69.1 Hz. McGlone~1967! found values ranging from 10.9 to52.1 Hz. Murry ~1971! obtained values of 22–92 Hz fovocal fry, and 73–98 Hz for the low modal register rangMcGlone and Shipp~1971! obtained values of 18–65 Hz fovocal fry. Average frequencies of vocal fry vibration, etrapolated from the literature, range from approximatelyto 70 Hz with a mean of approximately 50 Hz.

Women usually have a broaderF0 range than men inmodal register. In vocal fry register, a negligible differenin F0 range between males and females has been reporteMcGlone~1967!. McGlone found that theF0 range in vocalfry was from 10.9 to 51.0 Hz for males, and from 15.5

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48.8 Hz for females. Hollien and Wendahl~1968! obtainedsimilar findings for males~24–52 Hz!, and females~18–46Hz!. Acoustic parameters of pitch perturbation, shimmand signal-to-noise ratio do not appear to have been toughly investigated for vocal fry phonation.

B. Aerodynamic properties of vocal fry

1. Airflow

According to McGlone~1967!, vocal fry is producedwith an average airflow ranging from 2.0 to 71.9 ml/s. MGlone also found that, unlike modal register, airflow ratevocal fry did not increase as vocal fry frequencies increasMurry ~1971! reported that when vocal fry is sustained, tairflow rate is significantly reduced compared to modal rister; about 10–100 ml/s in vocal fry, and 70–180 ml/smodal register.

2. Subglottal air pressure

Murry ~1971! reported subglottal air pressure~Ps! dataduring vocal fry of 8.0–11.0 cm H2O. The values were significantly greater than those produced in the modal regi~5.0–6.0 cm H2O!. He concluded that Ps increased durithe long closing phase to force apart the large vocal fmass. However, McGlone and Shipp~1971! found that thePs ranged from 2.5 to 7.6 cm H2O for vocal fry, and from 2.8to 7.0 cm H2O for modal register. Differences between ttwo vocal registers were not significant. It is clear that tfindings of Murry ~1971! and McGlone and Shipp~1971!differ and additional research is warranted to further evaluthe vocal fold driving pressures in modal and vocal fry reisters.

C. Physiological properties of vocal fry

Vocal fry is characterized by a glottal area function thhas sharp, short pulses followed by a long closed glointerval ~Childers and Lee, 1991!. There is a very short opeperiod and a very long period where the vocal folds are copletely adducted. Due to the short open period in fry photion, the open quotient~OQ! of vocal fry is less than otheregisters. Childers and Lee~1991! examined four voice typesusing electroglottography~EGG!: modal, vocal fry, falsetto,and breathy. They found that the glottal pulse widths wsmaller ~25%–45%! in vocal fry phonation compared tmodal register, due to the shorter open phase. Murry~1971!suggested that the low airflow rate in vocal fry was relatedthe long closed phase of the vocal fold vibratory cycle.

Moore and von Leden~1958!, using high-speed laryngeal cinematography, found that during vocal fry the vofolds opened and closed twice in rapid succession. HoweHollien et al. ~1977! argued that Moore and von Lede~1958! used a rough type of phonation, and consequeobtained a ‘‘mixed’’ phonation which was not indicative otrue vocal fry. Later, Whiteheadet al. ~1984! using high-speed laryngeal photography found that the vocal fold vibtory patterns in vocal fry can be associated with singdouble, or triple opening and closing gestures followed blengthy closed period. The findings by Whiteheadet al.~1984! appear to support the conclusions of Moore and v

2650 J. Acoust. Soc. Am., Vol. 103, No. 5, Pt. 1, May 1998

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Leden~1958!, however further research seems warrantedverify the extent and characteristics of multiple opening aclosing gestures in vocal fry.

D. Perceptual properties of vocal fry

Vocal fry has been described as sounding similar to‘‘popping of corn,’’ the imitated sound of a ‘‘motor boaengine,’’ or a ‘‘creaky voice.’’ In essence, the vocal foldtend to vibrate so slowly that individual vibrations canperceived~Colton and Casper, 1996!. Hollien and Wendahl~1968! reported that theF0 of their vocal fry samples wasvery low, and the perceptual regularity of vocal fry provideevidence against classifying it as a voice pathology. Vofry may also be regarded as a lower extension of the norpitch range as brief vocal fry production is common at tvery end of sentences when pitch and vocal intensitybeginning to decay~Zemlin, 1988, p. 167!.

E. Summary

As vocal fry register is a portion of the full capability othe human vocal range, it appeared that further study shoenhance our knowledge of the complex process of phonatAttempts have been made to understand the phonatiproperties of vocal fry using a variety of measurement teniques~Childers and Lee, 1991; Hollien and Michel, 196McGlone and Shipp, 1971; Murry and Brown, 1971a; Whiheadet al., 1984!. Results from these studies vary consideably. To date no studies have measured simultaneouslyacoustic, aerodynamic, physiologic, and perceptual chateristics of vocal fry. The purpose of this research is to ingrate simultaneous measurement of vocal fry and modal pnational registers to better understand the aeromechamechanisms involved with vocal fry production.

I. METHOD

A. Subjects

Twenty normal nonsmoking adult speakers~10 malesand 10 females! with ages ranging from 22 to 65 years paticipated in the present study. Potential subjects wscreened for their ability to produce and sustain vocalphonation. Each subject’s ability to produce vocal fry wjudged by two of the experimenters. In order to be consered for inclusion in the present study, speakers werequired to produce approximately four seconds of vocal frytwo vowels ~/Ä/ and /i/!. Approximately 35 speakers werscreened. A total of 24 subjects were selected for recordbased on the screening task. Four subjects were subsequexcluded from the study due to their inability to maintavocal fry in all of the experimental tasks. Subjects werenative speakers of American English, and did not reportexhibit any voice, speech, language, or hearing problem

B. Speech material

Four vowels~/i/, /Ä/, /,/, /u/! were produced by the 20speakers in both modal and vocal fry registers. The vowwere randomized for each subject. For each register,vowels were sustained for approximately 6 s and were pro-

2650Blomgren et al.: Modal and vocal fry registers

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duced three times at a normal conversational loudness leEach speaker also produced a string of seven contiguoussyllables~/pipi...pi/! three times at normal loudness levelboth the modal and vocal fry registers. The speakers winstructed to take a full breath and produce the seven csecutive /pi/ syllables on one breath.

C. Recording procedure

Voice recordings were conducted in a single-wasound-isolated booth using an 8-channel PCM data reco~TEAC, RD-111T!. All recordings were digitized, thusavoiding low-frequency distortion inherent in traditional adiotape. Airflow, air pressure, EGG, and acoustic signwere recorded simultaneously on high quality digital tapThe acoustic signal was acquired via a dynamic microph~Shure, 515SP! and recorded on one channel of the digidata recorder. A mouth-to-microphone distance of 20was maintained. The EGG signal was obtained using a lagograph~Kay Laryngograph Ltd.! and recorded on a seconchannel of the digital data recorder. The EGG signal wsensed by two electrodes, which were placed directly oeach subject’s thyroid lamina. The electrodes were fixed oVelcro strip that was then placed around each speakneck. The airflow signal was obtained via a pneumachograph mask that was held securely against each subface by one of the researchers to avoid air leakage duringexperiment. Air pressure was measured via a 6.0-cm-lpolyethylene tube with an internal diameter of 2.5 mm. Ttube was passed through the pneumotachograph maskone end placed in the speaker’s mouth, and the otherattached to an air pressure transducer. The airflow andpressure signals were transduced by using a standarddynamic system~Rothenberg, 1973! and were amplified~Glottal Enterprise, MS100-A2! before being recorded. Thamplified airflow and air pressure signals were recordedtwo separate channels of the data recorder.

The airflow and air pressure signals were calibrated aeach recording. During the calibration, two different leveof airflow ~0.5 l/s, 1 l/s! and three levels of air pressur~0-cm H2O, 5-cm H2O, 10-cm H2O! were generated by using the Mask Calibration Unit~Glottal Enterprise, MCU-3!.All calibration signals were recorded on the PCM datacorder.

D. Analysis

The four signals~airflow, air pressure, EGG, and acoutic! were fed from the data recorder into a computer~80586,CPU! and analyzed by using an integrated compuhardware/software package~Kay Elemetrics, CSL-4300B!.The four signals were simultaneously displayed on foseparate windows on the computer monitor. For the stained vowel productions, only airflow and the acoustic snals were analyzed.

The sustained vowel airflow values were obtainedsuperimposing two markers on the digital flow waveformdelineate a 400-ms segment to be analyzed. The demarcsegment of the flow waveform was then expanded to cledisplay the individual peaks corresponding to the individ


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glottal pulses. The peak airflow of five glottal pulses wmeasured for each vowel repetition. Thus averaged airflmeasures from each subject~in each vowel and in each register! were calculated from 15 peak airflow measures~5 mea-sures per repetition33 repetitions!. For the /pi/ syllable pro-ductions, peak airflow was calculated on the middle fivethe seven /pi/ repetitions. Peak airflow in the /pi/ syllabrepetition task was measured from the baseline to the mmum point of excursion on the flow waveform following threlease of the stop phase of the /p/.

The acoustic analysis was performed on a 1500-steady-state segment from the center portion of eachtained vowel production. Vowel samples were digitized uing CSL at 20 000 Hz and converted to a waveform fiWaveform analysis~F0 , jitter, shimmer, and signal-to-noisratio! was conducted with PC-AUDED software~BostonUniversity!. Since the vocal fry acoustic waveform was chaacterized by relatively high variability, the automatic pitcperiod detection method was not used. Instead, pitch pemarkers were inserted manually at positive-going zero croings. The PC-AUDED program allows for a straightforwamethod of inserting pitch period markers. PC-AUDED scathe signal and automatically imposes the pitch period marat the exact zero crossing point closest to the manuplaced impulse marker. Once the pitch period segments wmarked, PC-AUDED computedF0 , jitter, shimmer, andsignal-to-noise ratio. Jitter was calculated as a percentagfrequency perturbation~ jitter factor!, which is the mean ofthe absolute difference between sequential vocalF0s ~in Hz!divided by the meanF0 . This proportion is then multipliedby 100 to attain the percentage score. Shimmer was calated as themean shimmer in decibelswhich is the sum ofthe absolute values of the differences between the curand the previous sample divided by the number of periminus one. Signal-to-noise ratio was calculated as the difence in dB of the average signal amplitude and the nosignal amplitude. Average signal amplitude and noise sigamplitude were first calculated as rms~root mean square!.Then, the average signal amplitude~rms! and the noise sig-nal amplitude~rms! were converted to dB using the following formula: dB520 log10 ~rms!.

Subglottal pressure was estimated for the vowel /i/measuring and interpolating the peak intraoral pressureing the stop phase of five /pi/ syllable repetitions~Lofqvistet al., 1982; Rothenberg, 1982; Smitheran and Hixon, 198!.The technique is based on the assumption that the vocal fare fully abducted before the release of the burst duringproduction of /p/. At that instant, the intraoral pressureequivalent to the subglottal pressure. For the /pi/ string, othe middle five syllable productions in the vocal fry anmodal registers were analyzed. Peak airflow and peakpressure values were recorded for the middle five prodtions of /pi/. All airflow and air pressure values were otained by using a linear regression function calculated frthe calibration signals.

The EGG signals were displayed using CSL. Each sigproduced in vocal fry register was compared to the EGsignal in modal register. Qualitative visual comparisons wmade and deviations in the EGG waveform between the


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2652 J. Acoust. S

TABLE I. Average fundamental frequency~Hz! and standard deviations in semitones~ST!, jitter factor ~%!,mean shimmer~dB!, and S/N ratio~dB! for the modal and vocal fry registers. Standard deviations areparentheses.

Males Females

Modal register Vocal fry Modal register Vocal fry

F0 ~ST! 117.5 ~2.3! 49.14 ~3.7! 211.0 ~2.0! 48.1 ~3.5!Jitter ~%! 1.23 ~.83! 14.9 ~7.1! 1.79 ~.53! 8.8 ~4.4!Shimmer~dB! 0.40 ~.21! 1.41 ~.66! 0.38 ~.20! 1.38 ~.82!S/N ratio ~dB! 13.27 ~3.87! 0.67 ~2.55! 12.84 ~3.75! 1.29 ~2.74!

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registers were noted. Specifically, the number of peakscycle were identified. In the present study, an EGG pattwith one opening/closing pattern per vibratory cycle widentified as asinglet. The EGG waveforms that containepatterns of more than one peak-per-cycle were identifiedcomplex repetitive. Complex-repetitive patterns could include both double peaks~doublet cycles! and triple peaks~triplet cycles!.

E. Perceptual identification of glottal fry

A perceptual task was conducted to determine if listers were able to differentiate between the modal and glofry registers. Forty recordings of the sustained vowel /Ä/ ~onemodal and one glottal fry production from each of thesubjects! were randomized and presented to a group oflisteners. Samples were presented in a sound field via eoverhead speakers. Listener-to-speaker distance ranged2 m to 5 m. Several samples of modal and vocal fry prodtion were presented to the listeners for practice beforeexperimental task. An additional 10 samples were randoselected from the original samples to serve as an intra-jureliability test. The listeners were undergraduate and graate students in the Communication Disorders program atUniversity of Connecticut. The undergraduate studentsno course-work in the area of voice, while the graduate sdents had a course in voice and some experience listeninvoice samples. In a forced-choice format, each listenerasked to rate the 50 samples as either modal or vocaregister.

II. RESULTS

A. Acoustic data

The F0 data for the male and female speakers inmodal and vocal fry registers are presented in Table Ithree-way analysis of variance~ANOVA !, with gender,vowel type, and register as independent variables, andF0 asthe dependent variable, was performed to determine ifnificant differences existed among the three independvariables. The analysis indicated no interaction betweenister and vowel type, or between gender and vowel type wrespect toF0 . There was a significant interaction betweregister and gender@F(1,159)5372.5,p,0.01#. A one-wayANOVA was performed within in each gender group to eamine whether significant differences existed between vofry and modal register. The findings indicated that a signcant difference existed between vocal fry and modal regi

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for both males and females with respect toF0 @male:F(1,79)5341.6, p,0.01; female: F(1,79)51355.1, p,0.01#. For the female speakers, the average modal regF0 was 211 Hz with a range of 175–266 Hz, and the avervocal fry registerF0 was 48 Hz with a range of 24–77 HzFor the male speakers, the average modalF0 was 117 Hzwith a range of 86–170 Hz, and the vocal fryF0 was 49 Hzwith a range of 24–72 Hz. There was a significant differenbetween female and male speakers in the modal reg@F(1,79)5342.4, p,0.01# but not in the fry register. Thefemale speakers had a higher meanF0 than the male speakers only in the modal register.

Separate three-way ANOVAs were performed for tjitter, shimmer, and signal-to-noise ratio~S/N! ratio values,to examine whether an interaction existed among regiand gender, register and vowel type, and gender and votype. The results indicated no interaction among these thindependent variables~register, gender, and vowel type! withrespect to the dependent variables of jitter, shimmer, orratio. The register main effect for jitter, shimmer and Sratio values were all significant@ jitter: F(1,159)5117.7,p,0.01; shimmer:F(1,159)5104.4, p,0.01; S/N ratio:F(1,159)5474.7,p,0.01#. Specifically, jitter and shimmevalues were significantly greater in vocal fry than in tmodal register for both males and females~see Table I!. S/Nratio values were significantly greater in modal register thin vocal fry register for both males and females~see Table I!.The main effect for vowel type was also significant for Sratio @F(3,76)514.3,p,0.01#. A Newman–Keulspost hoctest indicated that the S/N ratio, in modal register only, wsignificantly higher for /u/ than /,/ and /Ä/, and significantlyhigher for /i/ than /,/. A gender main effect was identifiewith jitter @F(1,159)568.0,p,0.01#. Specifically, jitter wassignificantly higher in the male speakers compared tofemale speakers only in the vocal fry productions.

B. Aerodynamic data

1. Airflow

Rate of airflow was measured for the four sustainvowels ~/i/, /,/, /u/, /Ä/! and for the stop consonant in thsyllable /pi/. Four one-way ANOVAs were conductedevaluate whether differences existed among the four stained vowels with respect to airflow. Vowel differencewere evaluated for each register in both gender groups.significant differences in flow rate values were noted amothe four vowels in either modal or vocal fry productionConsequently, airflow values were collapsed across the


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2653 J. Acoust. S

TABLE II. Average peak airflow rate values~ml/s! and air pressure values~cm H2O! for modal and vocal fryregisters. Airflow in the sustained condition was averaged across the four vowels. Standard deviationparentheses.

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Modal register Vocal fry Modal register Vocal fry

Airflow onSustained vowels

154.6 ~38.7! 58.2 ~28.2! 213.7 ~77.4! 69.7 ~35.0!

Airflow on /pi/Syllables

438.0 ~124.2! 175.1 ~77.5! 648.9 ~123.9! 258.0 ~87.8!

Air pressure on /pi/Syllables

7.56 ~1.93! 5.25 ~1.56! 7.45 ~1.88! 5.51 ~3.50!

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vowels for each gender and register group. The averageflow rates for the modal and vocal fry registers are reporin Table II.

A two-way ANOVA was performed for the flow ratevalues collapsed across the sustained vowels to examwhether differences existed between gender and register.results revealed a significant interaction between genderregister@F(1,158)513.6,p,0.001#. A Newman–Keulsposthoc test indicated that airflow rates for both males andmales were higher in modal register than in the vocalregister, however males had significantly higher airflow rathan females only in the modal register.

A two-way ANOVA was also performed on the flowrate values for /pi/ to determine if differences existed btween gender and register. No interaction was found betwgender and register. The gender main effect was significindicating that males exhibited significantly greater airflorates for /pi/ than females@F(1,26)590.7, p,0.0001#. Forboth males and females, the register main effect wassignificant indicating that airflow rates in modal register pduction were significantly greater than in vocal fry regis@F(1,26)518.3,p,0.0001#.

2. Air pressure

The average air pressure values for the intervocalic sin the /pi/ syllable are presented in Table II. A two-waANOVA was performed which revealed no interaction btween the two independent variables of gender and regiOnly the main effect for register was significant. For bomales and females, air pressure values in the modal protions were significantly higher than those in the vocalproductions@F(1,19)511.8,p50.003#.

C. EGG data

The EGG waveforms were evaluated for qualitative dferences between modal register and vocal fry. A visual coparison of EGG waveforms in modal register and singvocal fry production is provided in Fig. 1. The EGG wavforms that contained patterns of more than one peak-cycle were identified as complex repetitive. Both doublet atriplet cycle patterns were observed in the complex-repetiwaveforms~see Fig. 2!. The triplet cycles were always observed in association with doublet cycles, while the doubcycles did not necessarily accompany triplet cycles.

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For the male speakers’ vocal fry productions, 99 of t120 EGG waveforms that were analyzed contained comprepetitive patterns~83%!. For the female speakers’ vocal frproductions, 45 of the 120 EGG waveforms containcomplex-repetitive patterns~38%!. A Mann–Whitney U-testwas conducted to assess whether gender differences exwith respect to prevalence of complex-repetitive patterMales’ vocal fry productions were characterized by a signcantly higher prevalence of complex-repetitive patterns ththe females’~U515.5, p50.007!. Of the 83% of the maleproductions that contained complex-repetitive patterns, 5contained only doublet cycles and 44% contained a comnation of doublet and triplet cycles. Of the 38% of the femaproductions that contained complex-repetitive patterns, 8were characterized by the presence of only doublet cyand 13% contained both doublet and triplet cycles.

D. Perceptual data

Responses from the 55 listeners were calculated andvided into two groups: scores for the modal productions ascores for the vocal fry productions. A total of 2200 rsponses were recorded from the listeners~55 listeners340tokens!. The individual listener scores on the 20 modal prductions ranged from 16 to 20 correct responses~M519.04, s.d.51.27!. Of the 1100 responses pertaining to tmodal productions, 1050 were classified correctly as moor 95.5% correct. Of the 1100 responses corresponding tovocal fry production, 100% were correctly identified by thlisteners as vocal fry.

Intra-judge reliability was determined by comparing rsponses for each listener on 10 randomly selected samthat were presented a second time. An intra-judge reliabscore of 99.3% was obtained. Agreement was obtained546/550 responses.

III. DISCUSSION

The main purpose of this study was to compare acousaerodynamic, EGG, and perceptual properties of vocal fvibration during modal and vocal fry conditions. Eacspeaker acted as his/her own control. Comparisons of spsamples produced in the modal and the vocal fry regiswere made for each speaker.


FIG. 1. Illustrations of modal and vocal fry production. Both frame 1 and frame 2 are of the same male speaker producing /Ä/. Panel A~channel 1! in boththe modal and vocal fry frames contain the acoustic signal. Panel B~channel 2! contains the EGG signal. In modal register the speaker’sF0 was 122 Hz whilein vocal fry hisF0 was 33 Hz. The illustrated vocal fry production is characteristic of a single pulsing~singlet! pattern.

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A. Acoustic measures

1. Fundamental frequency

Considerable differences between modal and vocalregisters were observed in the present study. Both malefemale speakers exhibited significantly reducedF0 values invocal fry compared to modal register. These findings agwith the results reported by Hollien and Wendahl~1968!,McGlone ~1967!, and Murry ~1971!. No intra- or inter-speaker overlap inF0 between modal and vocal fry was observed. These findings also agree with Hollien’s~1974! de-scription of voice register.

The female speakers exhibited significantly higherF0

values than the male speakers in the modal register. Hever, the averageF0 values for the female speakers durinvocal fry phonation were not significantly different from thof the male speakers. These findings are in agreementthose reported by McGlone~1967! and Hollien and Michel~1968!, who suggested a distinct vocal fold vibratory behaior when comparing vocal fry and modal registers.

While general anatomical differences between malefemale larynges is often assumed to account for differenin modal F0 , these anatomical differences may not berelevant when considering vocal fry. For both male andmale speakers’ vocal fry production, it is possible that vofold vibration only occurs over a small portion of the foldZemlin ~1988! reported that examination of vocal fry withigh speed photography revealed ‘‘the folds are appromated tightly, but at the same time they appear flaccid al


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their free borders, and subglottal air simply bubbles uptween them at about the junction of the anterior two-thirdsthe glottis’’ ~p. 166!. If vocal fold vibration in vocal fry doesindeed occur over a small portion of the total vocal folength, then the intrinsic longitudinal length of the vocfolds may be less of a mitigating factor in determining trate of vibration.

Although only part of vocal folds may be vibrating ivocal fry, the intrinsic mass of the vocal folds for male afemale speakers may still be inherently different. One migtherefore, still predict gender differences in vocal fryF0

based on vocal fold mass differences. An alternate ‘‘vocontrol’’ theory may aid in explaining the absence of genddifferences in vocal fryF0 as found in the present studySince vocal fry is not typically used by the speakers, gendifferences may be obscured. Both the male and femalejects could have adopted the same external standard of alow fundamental frequency. The similar vocal fryF0 rangesfor males and females may be influenced by the speaattempt to attain the same task of vocalizating in the s60-Hz range.

2. Jitter, shimmer, and S/N ratio

Gender differences for signal-to-noise~S/N! ratio andshimmer values under both vocal fry and modal register cditions were not significant. However, the male subjectshibited significantly higher jitter values in vocal fry production compared to the female subjects. Jitter factor values


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FIG. 2. Illustrations of complex-repetitive vocal fry waveforms. Frame 1 and frame 2 are of two different male speakers producing /Ä/. Panels A~channel 1!contain the acoustic signal and panels B~channel 2! contain the EGG signal. In the upper frame, double pulsing~doublet! vibratory cycles are displayed a28 Hz. In the lower frame, triple pulsing~triplet! cycles are displayed at 24 Hz.
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modal register production in the present study~M males:1.23%; M females: 1.79%! were slightly higher than thosreported elsewhere, which are typically slightly less than~Hollien et al., 1973; Murry and Doherty, 1980; Sorenseand Horii, 1983!. Shimmer values for modal register prodution in the present study~M males: 0.40 dB;M females: 0.38dB! appeared very similar to previous studies. Horii~1980!reported an average shimmer value across adult male0.39 dB and Sorensen and Horii~1983! reported an averagshimmer value for adult females of 0.25 dB.

Significant differences in S/N ratio, shimmer, and jittvalues were present between the modal and fry regisWhen compared to modal register, the vocal fry register wassociated with significantly reduced S/N ratio and greajitter and shimmer values. In vocal fry, higher jitter anshimmer values indicate decreased phonatory stability infrequency and amplitude domains. Decreased S/N ratiothe vocal fry signal indicates a higher noise energy comnent relative to the periodic energy component when copared to modal register.

B. Aerodynamic measures

1. Rate of airflow

Rate of airflow was significantly reduced in the vocal fregister when compared to the modal register~see Table II!.Rate of airflow in the modal register was reported previouto be 70–200 ml/s~Hirano, 1981!. Modal register airflowrates in the present study were slightly higher~M


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males5214 ml/s; M females5155 ml/s! than those reportedby Hirano ~1981!. Vocal fry airflow results in the presenstudy ~M males570 ml/s; M females558 ml/s! were alsohigher than values reported by McGlone and Shipp~1971!(M540.4 ml/s).

The present results also indicate that the rate of airflbetween male and female speakers was not significantlyferent in vocal fry. This appears to further support the notof a similar vocal fold vibratory pattern for both male anfemale speakers during vocal fry when compared to movoice production~Hollien et al., 1966!.

2. Air pressure

Significantly reduced subglottal pressure values weresociated with the vocal fry condition for both males afemales~see Table II!. The present results are in agreemewith the findings of Murry and Brown~1971b!, who foundlower subglottal pressure values for vocal fry than moregister in connected speech. The present subglottal presfindings, however, do not support the results reportedMurry ~1971!. Murry ~1971! found that subglottal pressure isustained vocal fry production was significantly higher ththat in modal register. The discrepancy in findings maydue to the different measurement techniques used. M~1971! used a tracheal puncture technique to measureglottal pressure. In the present study, subglottal pressureestimated for the vowel /i/ by measuring and interpolatithe peak intraoral pressure during the stop phase of sev


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/pi/ syllable repetitions. Although one may argue for thecreased validity of the more direct tracheal puncture tenique, Murry’s five subjects were tested in a nonstandsupine position, compared to a more natural upright speaposition. The absence of gravity on true and ventricularcal folds in the rostral-caudal~inferior-superior! dimensionmay influence the vocal fold vibrating pattern.

As described above, vocal fry phonation has been chacterized by a condition of closely adducted vocal folds wsimultaneously~relatively! flaccid vocal fold margins~Zem-lin, 1988!. The vocal fold margins are flaccid becausedecreased longitudinal tension. It is suggested that lesspressure is required to set the flaccid vocal fold marginsvibration when compared to the taut vocal margins in moregister. In addition, it was observed that the subjects inpresent study tended to produce the ‘‘best’’ vocal fry photion when their fry production was perceived to be relaxwith no perception of tension. The present findings of dcreased subglottal pressure indirectly supports the notionreduced vocal fold tension may be required to produce vofry.

Glottal resistance can also be used to characterize vfry and modal registers. Glottal resistance is calculateddividing the transglottal pressure differential by glottal aflow (R5DP/Q) ~Smitheran and Hixon, 1981!. In thepresent study, the average resistance values w11.5-cm H2O/l/s for males and 17.5-cm H2O/l/s for femalesin modal register. In vocal fry, the average resistance vawere 21.4-cm H2O/l/s for males and 30.0-cm H2O/l/s for fe-males. The average glottal resistance values were highvocal fry than in modal register for both males and femalIn order to increase glottal resistance, subglottal pressurecreases while flow rate remains constant, or flow ratecreases while subglottal pressure remains constant. Inpresent study, resistance was increased due to a decreaboth subglottal pressure and flow rate, however, flow rdecreased to a greater extent than subglottal pressure.

C. EGG analysis

The results of the EGG waveform analyses revealedthe vibratory patterns associated with vocal fry may be chacterized by single opening and closing, or multiple openand closing patterns during a single vibratory cycle~doubletand triplet cycles!. These findings support previous researindicating that the vocal folds are capable of multiple vibtion patterns~Hollien and Wendahl, 1968; Moore and voLeden, 1958; Timckeet al., 1959; Whiteheadet al., 1984!.

Some researchers have suggested that doublet or trvibratory patterns occur as a result of ‘‘mixed’’ phonatiothat contains elements of both vocal fry and modal regis~Hollien et al., 1977; Wendahlet al., 1963!. We would tendto argue against this position as the vocal fry productionsthe present study were consistently identified by the judin the perceptual task as vocal fry. In addition, our obserlow mean frequencies for vocal fry~below 50 Hz for bothmales and females! mitigates against classification asmixed type of phonation.


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Vocal fry phonation appears to be associated wclosely approximated vocal folds, which is supported bypresent findings of lower airflow and increased glottal restance when compared to modal register. During vocalthe arytenoid cartilages may be pressed anteriorly and mally causing the posterior portions of the vocal folds toheld together. The vocal folds become short and thick wonly the anterior ligamental portions vibrating. The vocfold margins, however, remain relatively flaccid becausedecreased longitudinal tension~Zemlin, 1988, p. 166!. Allenand Hollien ~1973! and Hollien ~1974! reported that meanvocal fold thickness was greater in vocal fry than in modregister. The thicker and more compact true vocal folds maccount for the obtained complex-repetitive pattern in soof the vocal fry EGG waveforms. The doublet or triplet paterns may be representative of double or triple oscillatio~per cycle! along the free margin of the vocal folds durinvocal fry phonation.

Another explanation for the observed complex-repetitpatterns is based on the x-ray image findings of Allen aHollien ~1973!. They found that the inferior surfaces of thventricular folds may contact the superior surface of the tvocal folds during vocal fry phonation. The subseque‘‘thick’’ vibrating structure may contribute to the similarityin F0 between males and females. In addition,the compvibratory activity of the coupled ventricular and true vocfolds may also contribute to the complex-repetitive patteing.

D. Perceptual identification of vocal fry

In the perceptual study, 55 listeners correctly identifi95.5% of the experimentally classified modal productions/Ä/ and 100% of the vocal fry productions. These findinindicate that perceptual differences are discerned betwthe experimentally classified modal and vocal fry produtions. The high agreement between the acoustic, aeronamic, and EGG distinctions and the perceptual distinctof vocal fry and modal productions appear to add validitythe classification of these distinct registers.

IV. CONCLUSIONS

The findings in the present study attempted to increpresent knowledge regarding phonation in vocal fry regisAcoustic findings indicated there was a significant differenin F0 between males and females in modal register, whgender differences in vocal fry register were not observFor both males and females, jitter and shimmer valuesvocal fry were significantly higher than those in modal reister indicating greater frequency and amplitude perturbain vocal fry. The S/N ratio values in vocal fry register wesignificantly lower than those in modal register, possiblydicating less efficient valving of the vocal fold mechanismthe vocal fry register. In addition, differences in airflow, apressure, glottal resistance, and EGG characteristics widentified between modal register and vocal fry registerboth males and females.

Vocal fold vibration is the result of a delicate balancesubglottal air pressure driving the folds apart, and the m


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cular, elastic, and Bernoulli forces that bring them togethIn modal register, the vocal folds vibrate in a relatively cosistent manner, with the movement of a wave along the vomargin that propagates superiorly. These movements hbeen characterized by the two-mass model of vocal foldbration~Ishizaka and Matsudaira, 1968; Titze, 1981!. Vibra-tion of the vocal folds in vocal fry appears to be more coplex. While a two-mass model provides a succinct accounphonation in modal register, the complex differencesserved in vocal fry phonation will likely require descriptiousing a multi-mass model. In order to model the compvibration patterns in both the anterior/posterior plane asuperior/inferior plane of the vocal folds, simultaneouscordings using EGG, acoustic,anddirect visualization incor-porating high-speed filming or stroboscopic techniquespears necessary.

The differences between modal and vocal fry registwith respect to acoustic, aerodynamic, and EGG parameare believed to be due to two distinct aeromechanical moof vocal fold vibration. During phonation in the modal reister, the vocal folds appear to be tightly adducted alonganterior margins, with the presence of a commonly obserposterior glottal chink~Broad, 1973!. In vocal fry, the vocalprocesses of the arytenoids appear to be pulled inwardforward. The posterior glottal chink may be greatly dimiished in vocal fry. The thyroarytenoid muscles tendshorten, and subsequently thicken the antero-posteriormension of the vocal folds, allowing the anterior part of tvocal ligaments to vibrate~Allen and Hollien, 1973; Hollien,1974!. As the thyroarytenoid muscle shortens, the vocal fmargins also become more flaccid. The thickening ofvocal folds in combination with decreased vocal ligamestiffness during vocal fry may be two prime factors contruting to the reduced rate of vocal fold vibration, which cosequently alter the characteristics of the vibratory cycle.

In the present study, vocal fold vibration in the modregister was maintained by subglottal pressure values ofproximately 7.5-cm H2O, which counteracts the longitudinatension and medial compression of the thyroarytenmuscles~Borden et al., 1984!. In vocal fry, however, thesubglottal pressure values were approximately 5.5-cm H2O,possibly indicating reduced tension and medial compressThe finding of increased glottal resistance in vocal fry mbe explained by the increased vocal fold mass, rather tincreased longitudinal tension and medial compressionindeed, the vocal folds are less tense in vocal fry thanmodal register, then it would appear that less subglottal ding pressure is required to force them apart. We further sgest that reduced subglottal pressure is not just a coquence of vocal fry, but that individuals actively redusubglottal pressure as an aerodynamic strategy to facilachieving fundamental frequencies below 60 Hz.

In conclusion, it was found that vocal fry was distinguishable from modal register production in acoustic, aedynamic, physiologic, and perceptual measures. Futuresearch regarding the precise degree of vocal fold adducdegree of vocal fold margin stiffness, and the precise moments of the vocal fold margins and contribution of the ve


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tricular folds will help to further describe the interesting lryngeal phenomenon of vocal fry.

ACKNOWLEDGMENTS

Portions of this paper were presented at the 133rd ming of the Acoustical Society of America, June 1997 in StaCollege, Pennsylvania. We wish to thank Dr. AndeLofqvist, Dr. Michael Robb, and two anonymous reviewefor their excellent comments on an earlier version of tmanuscript.

Allen, E., and Hollien, H.~1973!. ‘‘A laminagraphic study of pulse~vocalfry! phonation,’’ Folia Phoniat.25, 241–250.

Borden, G. J., Harris, K. S., and Raphael, L. J.~1984!. Speech SciencePrimer: Physiology, Acoustics, and Perception of Speech~Williams &Wilkins, Baltimore, MD!, 3rd ed.

Broad, D. J.~1973!. ‘‘Phonation,’’ In Normal Aspects of Speech, Hearingand Language,edited by F. D. Minifie, T. J. Hixon, and F. Williams~Prentice-Hall, Englewood Cliffs, NJ!.

Childers, D. G., and Lee, C. K.~1991!. ‘‘Vocal quality factors: Analysis,synthesis, and perception,’’ J. Acoust. Soc. Am.90, 2394–2410.

Colton, R. H., and Casper, J. K.~1996!. Understanding Voice Problems~Williams & Wilkins, Baltimore, MD!, 2nd ed.

Daniloff, R., Shuckers, G., and Feth, L.~1980!. The Physiology of Speechand Hearing~Prentice-Hall, Englewood Cliffs, NJ!.

Hirano, M. ~1981!. Clinical Examination of Voice~Springer-Verlag, NewYork!.

Hollien, H. ~1974!. ‘‘On vocal registers,’’ J. Phon.2, 25–43.Hollien, H., and Jackson, B.~1973!. ‘‘Normative data on the speaking fun

damental characteristics of young adult males,’’ Journal of Phonetic1,117–120.

Hollien, H., and Michel, J.~1968!. ‘‘Vocal fry as a phonational register,’’ J.Speech Hear. Res.11, 600–604.

Hollien, H., and Wendahl, R. W.~1968!. ‘‘Perceptual study of vocal fry,’’ J.Acoust. Soc. Am.43, 506–509.

Hollien, H., Girard, G. T., and Coleman, R. F.~1977!. ‘‘Vocal fold vibratorypatterns of pulse register phonation,’’ Folia Phoniat.29, 200–205.

Hollien, H., Michel, J., and Doherty, E.~1973!. ‘‘A method for analyzingvocal jitter in sustained phonation,’’ J. Phon.1, 85–91.

Hollien, H., Moore, P., Wendahl, R., and Michel, J.~1966!. ‘‘On the natureof vocal fry,’’ J. Speech Hear. Res.9, 245–247.

Horii, Y. ~1980!. ‘‘Vocal shimmer in sustained phonation,’’ J. Speech HeRes.23, 202–209.

Ishizaka, K., and Matsudaira, M.~1968!. ‘‘Analysis of the vibration of thevocal cords,’’ J. Acoust. Soc. Jpn.24, 311–312.

Krook, M. ~1988!. ‘‘Speaking fundamental frequency characteristics of nmal Swedish subjects obtained by glottal frequency analysis,’’ Folia Pniat. 40, 82–90.

Lofqvist, A., Carlborg, B., and Kitzing, P.~1982!. ‘‘Initial validation of anindirect measure of subglottal pressure during vowels,’’ J. Acoust. SAm. 72, 633–635.

McGlone, R. ~1967!. ‘‘Air flow during vocal fry phonation,’’ J. SpeechHear. Res.10, 299–304.

McGlone, R., and Shipp, T.~1971!. ‘‘Some physiologic correlates of vocalfry phonation,’’ J. Speech Hear. Res.14, 769–775.

Moore, G. P., and von Leden, H.~1958!. ‘‘Dynamic variations of the vibra-tory pattern in the normal larynx,’’ Folia Phoniat.10, 205–238.

Murry, T. ~1971!. ‘‘Subglottal pressure and airflow measures during vofry phonation,’’ J. Speech Hear. Res.14, 544–551.

Murry, T., and Brown, W. S.~1971a!. ‘‘Regulation of vocal intensity duringvocal fry phonation,’’ J. Acoust. Soc. Am.49, 1905–1906.

Murry, T., and Brown, W. S.~1971b!. ‘‘Subglottal air pressure during twotypes of vocal activity: Vocal fry and modal phonation,’’ Folia Phonia23, 440–449.

Murry, T., and Doherty, E.~1980!. ‘‘Selected acoustic characteristics opathologic and normal speakers,’’ J. Speech Hear. Res.4, 321–328.

Rothenberg, M.~1973!. ‘‘A new inverse-filtering technique for deriving theglottal air flow waveform during voicing,’’ J. Acoust. Soc. Am.53, 1632–1645.

Rothenberg, M.~1982!. ‘‘Interpolating subglottal pressure from oral pressure,’’ Journal of Speech & Hearing Disorders47, 218–224.


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cs

s,’

ldsi-

st.

iol-

Smitheran, J. R., and Hixon, T. J.~1981!. ‘‘A clinical method for estimatingair way resistance during vowel production,’’ J. Speech Hear. Disord.46,138–146.

Sorensen, D., and Horri, Y.~1983!. ‘‘Frequency and amplitude perturbatioin the voices of female speakers,’’ J. Commun. Disord.16, 57–61.

Stoicheff, M. L. ~1981!. ‘‘Speaking fundamental frequency characteristiof nonsmoking female adults,’’ J. Speech Hear. Res.24, 437–441.

Timcke, R., von Leden, H., and Moore, P.~1959!. ‘‘Laryngeal vibrations:measurement of the glottic wave, part 2. Physiological variationAmerican Medical Assoc. Archives of Otolaryngology69, 438–444.


’

Titze, I. R.~1981!. ‘‘Biomechanics and disturbed-mass models of vocal fovibration,’’ in Vocal fold physiology, Proceedings of the vocal fold phyology conference,edited by K. Stevens and M. Hirano~University ofTokyo, Tokyo, Japan!, pp. 245–270.

Wendahl, R., Moore, P., and Hollien, H.~1963!. ‘‘Comments on vocal fry,’’Folia Phoniat.15, 251–255.

Whitehead, R. W., Metz, D. E., and Whitehead, B. H.~1984!. ‘‘Vibratorypatterns of the vocal folds during pulse register phonation,’’ J. AcouSoc. Am.75, 1293–1297.

Zemlin, W. R.~1988!. Speech and Hearing Science: Anatomy and Physogy ~Prentice-Hall, Englewood Cliffs, NJ!.


Acoustic, aerodynamic, physiologic, and perceptual properties of modal and vocal fry registers

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