Visual observations of glottic activity during didgeridoo performance

Krzysztof Izdebski, Lydia Hyde, Ronald R. Ward, Joel C. Ross, Pacific Voice and Speech Foundation, 3838 California Street # 505, San Francisco, CA 94118, USA

This paper was presented at the XX Annual Pacific Voice Conference

Optical Imaging, Therapeutics, and Advanced Technology in Head and Neck Surgery and Otolaryngology

Conference Program Track: Photonic Therapeutics and Diagnostics Available in print as Proceedings of SPIE Volume 8207C

PVSF/SPIE held January 21, 2012 – 08:00 AM to January 23, 2012 – 6:00 PM at Moscone Center San Francisco, CA 94103

ABSTRACT

The Australian didgeridoo is a reed-less hollow conically shape wooden tubular wind instrument typically measuring up to 150 cm in length, with distal and proximal diameters ranging from 150 to 30 mm. This tube allows a player to produce only a narrow variety of sound and sounds effects because it is coupled directly to the player’s vocal tract. The typical frequency of the tube typically called the drone, is approximately within 60 to 100 Hz range. This tone generation created by lip vibration is supported by circular breathing, allowing for an uninterrupted (indefinite) length of sound generation. Inhalation introduces sound pulsation, while specific tonal effects can be consciously created by manipulation of the player’s lips and/or the vocal tract, including conscious phonation using vocal folds vibration, all used to enrich both the sound and the artistic meaning of the played sequence.

Though the results of the research on the acoustics of this instrument are often reported in the literature, physiologic data regarding vocal tract configurations, and especially on the behavior of the vocal folds in regulation of ventilation and in phonation, remain less than underreported.

The data presented here comprises –as far as we were able to determine– the first ever physiologic account of vocal fold activity in a didgeridoo player observed with help of trans-nasal endoscopy. Our focus was to reveal the work of the vocal folds and of the supraglottic posturing of the glottis for 1) ventilatory, and 2) phonatory activity during playing.

Keywords: glottis, vocal folds, vocalization, ventilation, didgeridoo, circular breathing

1. INTRODUCTION

Playing a didgeridoo – an Australian aborigine musical instrument (also called yidaki, artawirr, djibolu, kurmur, martba, etc,depending on the many tribal languages of the Aboriginal people in Australia) is a reed-less wooden wind instrument. Its elongated construction limits the frequency of its acoustic output to approximately 60-100 Hz, range. The output is produced by lip vibration coupled with the player’s vocal tract configurations. This primary tone or drone is then modulated by conscious manipulations of the player’s lip vibration patterns, tongue positioning and vocalizations. Additionally, the output is passively modulated by the intrinsic characteristics of the didgeridoo tube. Typically, the tube is made of a hollowed-out eucalyptus branch, measuring on the
average 155 cm in length with a conical cross-section diameter ranging from 30 mm at the proximal end up to 120 mm distally. The player places the mouth at the proximal end of the tube (Figure 1) exhaling into it in circular breathing fashion.

Circular breathing is physiologically a very complicated ventilatory process, requiring simultaneous inhalation, storing of residual air in oral cavity and expelling air from the lungs at the same time while inhaling rapidly through the nose. This process requires the mouth cavity to be filled with air, followed up by the closing of the oral cavity with soft palate occlusion to sustain the sound, while another quick breath is taken trans-nasally. This allows for continuous sound production in an almost indefinite sequence. Such rapid inhalation pattern, forms pulsation of the tone, which can be further enhanced by modulated variations in expiratory blowing pressure, by lip motions, by vocal tract reconfiguration, and finally by active vocalization produced at the glottic level by consciously synchronized vibrations of player’s vocal folds. [1]

This ventilatory pattern defies completely the normal 12 breaths per minute (on the average) breathing pattern or even from breathing cycle prolongation pattern experienced by a classical vocalist. Circular breathing can also be used in some western wind instruments, but not to such a degree as required by a didgeridoo performer. Because of the inherent pitch variation limitations imposed by the didgeridoo itself, performers may introduce simultaneous vocalization using vocal folds vibrations to enhance performance quality and to vary pitch repertoire.

Although the didgeridoo is an instrument used for artistic purposes, interestingly enough, the complicated ventilatory mechanics have been applied to solve some clinical ventilatory issues. Evidence suggest significant clinical benefits are to be expected for
sleep apnea and asthma patients who learn how to play the didgeridoo. [2-3]

Although a number of studies concerning the acoustics of the didgeridoo have been published, [4-11] the mystery of understanding didgeridoo laryngeal physiology remains the rule, rather than an exception. This is surprising, since such knowledge is crucial in understanding and explaining the intricacies of the art and challenges of this unique instrument. Moreover, literature clearly states that the action of the vocal cords in wind instrument players has significant influence on pressures and tone generation, as the
skilled players narrow the glottis to provide a significant interaction between the upper vocal tract and the lungs.They serve to isolate the upper-tract resonances to a large extent from the damping influence of the resistive lung impedance”, hence it is “therefore
evident that the vocal folds can have a significant effect on the resonances of the vocal tract provided they are well adducted”. [12-13]
Consequently we feel that the data generated by us in this project complements well the few physiologic studies published hitherto with regard to didgeridoo mechanics, of which one included stroboscopic examination of lip activity and one reported on fMRI /MRI
studies of the shape of the supra-glottic vocal tract [8] and contributes the our knowledge of laryngeal physiology in wind instruments at large.

2. Materials and Method

Placement of the naso-fiberscope through the L nostril. Note cheek respiratory expansion during playing.
Figure 2. Placement of the naso-fiberscope through the L nostril. Note cheek respiratory expansion during playing.

The didgeridoo used in this study was made in Santa Barbara, CA, USA out of a Yucca stalk. It measured 177.5 cm in length. The mouth outlet diameter measured 35 mm, while the distal outlet measured 80 mm in cross-section.

Figure 2 shows the player in a sitting position, mouth on the instrument and with the fiberoptic scope inserted into the supraglottic cavity via the L nostril, that was previously prepared with local anesthetic.

We used a fiber-optic endoscope (Olympus ENF-P4) with xenon light source to observe the activity of the glottis in the act of playing a standard length didgeridoo.

All images (Figure 3) were recorded on a VHS system using standard Ecleris ENDODIGI System, Model EN102 (Ecleris, San Diego, CA 92128)

Images of the glottis obtained via transnasal fiberoptic endoscopy.
Figure 3. Images of the glottis obtained via transnasal fiberoptic endoscopy.

 

The image on the L represents a narrowly abducted glottis at the beginning of rapid inspiratory cycle, demonstrating reduction of the posterior glottis commissure. The middle image shows glottis toward termination of respiration, and the L image shows glottic compression prior to initiation of the new “pumping” action. Note progressive compression of
the supraglottic larynx, elevated VLP and forward displacement of the epiglottis.

Once obtained, all images were analyzed visually for motion. The performer we studied was an informed and consenting female didgeridoo artist with 20 years of experience in playing this instrument. The fiberoptic scope was passed trans-nasally in a standard manner, with light topical applied to numb the L nostril.

All images were recorded on a color digital (ENDOGIDI system, Ecleris, San Diego, CA 92128) using standard NTSC recording rate of 30 frames per second for post acquisition analysis to generate a MWF. file. Audio signal was recorded on Ecleris system via a clip-on microphone.

All recordings were done in three conditions.

1: In condition one, vocal folds activity was recorded a) during respiration and b) during vocalization, in
the absence of didgeridoo coupled to the mouth.
2: In condition two, didgeridoo sound was produced. In this mode, sound was modulated by lip
vibration, and the vocal folds were not in phonatory mode.
3: In condition three, the performer added active vocalization by engaging vocal folds activity to
generate sound in addition to the sound produced by the lip vibration.

Following observations and measurements were taken.

1: Visual inspection of supraglottic structures.
2: Behavior of mucosal wave.
3: Analysis of EGG signal.
4: Analysis of acoustic signals.
5: Configuration of the vocal folds in mm
6: Speed of vocal folds abduction and adduction measured in msecs.

3 RESULTS

3.1. Visual inspection of ventilatory position of the vocal folds:

A: Respiratory (inhalatory) positioning in control position of the vocal folds (non-didgeridoo) was estimated to be approximately 11 mm. at the posterior commissure. This was normally expected distance between the arytenoids for normal breathing.
Respiratory (inhalatory) positioning of the vocal folds in didgeridoo condition was estimated to be approximately 7 mm. at the posterior commissure respectively. The adduction time was estimated to take 150 msec for VC closure in control position. This
closure time approximated 100 -120 msec for glottis mobility during circular breathing. Phonatory position for the generated pitch was typical for age and gender and the generated pitch.

B: Respiratory trajectory for the experimental condition (not paying the instrument) was estimated
to 11 mm.

C: When circular breathing occurred and when vocalization was added, the width of respiratorytrajectory of the vocal folds at the posterior commissure was estimated to be 7 mm. or less.

3.2. Supraglottic behavior:

A: Epiglottis: Epiglottis was never folding completely over the glottis. Epiglottis however moved rapidly toward the posterior pharyngeal wall during inhalatory portion of circular breathing.

3.2.1. False Vocal Folds (FVF):

FVF moved slightly into midline during: a) end of respiratory pumping, and b) during prolonged
vocalization.
FVF remained non-contracted during control ventilation.

3.2.2.Vertical larynx position (VLP):

Entire larynx elevated a) during inhalation and b) during prolonged vocalization

4: Circular breathing effects:

Respiratory cycle was repeated 34 times during 1m 17 sec 58 msec duration of the entire
recorded segment. Based on these measures, circular breathing pumping rate was 1/ 2.29 sec.
During phonation respiratory cycling was subject to phonation length and the rate of 2.29 seconds
did not applied. Rate slowed down to approximately 1 repetition per 5 sec.

5: Duration:

This recording covered 77.58 seconds of uninterrupted playing. The average sustained vocal tone during simultaneous droning was 4.95 sec. Duration factor did not affect vocal folds activity in any perceivable manner. VLP showed elevation towards prolongation of tone.

6: F0 characteristics of the generated tones:

A: The drone tone varied from 70 Hz to 100 Hz.
B: The F0 of the voice varied form 250 Hz to 750 Hz.

4. Conclusions

As far as we can determine, this constitutes the first ever evaluation of glottic behavior during didgeridoo performance. Based on fiberoptic visualization we concluded that the behavior of the vocal fold differed for ventilatory trajectory between non-didgeridoo and didgeridoo conditions. Wider posterior abduction was present during non-didgeridoo breathing, and reduction of posterior commissure trajectory was present during circular breathing and drone making. This observation of narrowing of the glottis agrees with previous reports in the literature reporting for the first time that narrowing of the glottis in wind instrument players has a significant value to pressure regulation [12-13]. In our case, we feel that narrowing of the glottis helps to fulfill the need for rapid air exchange and intra-oral air storage. We speculate that such narrowing is also part of athletic activity. Also, interestingly the estimate of approximately 120 msec for adduction of the vocal folds during circular breathing fits the fastest
reactions time for vocal folds [14]

It seems that the phonatory vocal fold posturing was not affected when compared to no-drone and drone tone generation, meaning that vocal folds behaved in similar manner when the person produces didgeridoo or non-didgeridoo pitches. This may be however an inaccurate observation, because we could not observe unequivocally the cycle-by-cycle characteristics of non-didgeridoo and didgeridoo vocalization, and because most recent evidence form high speed digital recordings of vocal cord activity
in compressed and relaxed modes ([15] clearly showed significant glottic area function differences. This speculation is also supported by subjective opinion of the didgeridoo performer, who typically experience vocal instability and vocal fatigue after playing the didgeridoo and vocalizing into the tube. We hence suspect that the glottis cycle area function is affected by the didgeridoo. Evidence from fiberoptics support this speculation, since the true vocal folds were judged to be slightly more compressed during didgeridoo vocalization than during controlled vocalization. Didgeridoo vocalization was accompanied also by clearly visible FVF and supraglottic approximation and an increase in rapid VLP. Elevation of VLP has been linked to a decrease voice efficacy [16]
Based on this preliminary result, we conclude that didgeridoo playing introduces alternations both to the phonatory component, and to the ventilatory components. Further studies utilizing aerodynamics, EGG and stroboscopic visualization are planned.

5. REFERENCES

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[2] Eley R, Gorman D, Gately J. Didgeridoos, songs and boomerangs for asthma management. Health Promot J Austr. 2010 Apr;21(1):39-44.

[3] Kreuter M, Kreuter C, Herth F. Pneumological aspects of wind instrument performance–physiological, pathophysiological and therapeutic considerations. Pneumologie. 2008 Feb;62(2):83-7. Epub 2007 Dec 13.

[4] Tarnopolsky, A, Fletcher, N. Hollenberg, L., Lange, B., Smith, J. and Wolfe, J. (2005) “The vocal tract and the sound of a didgeridoo”, Nature, 436, 39.

[5] Tarnopolsky, A, Fletcher, N. Hollenberg, L., Lange, B., Smith, J. and Wolfe, J. (2006)”Vocal tract resonances and the sound of the Australian didjeridu (yidaki) I: Experiment”, J. Acoust. Soc. America , 119, 1194-1204.

[6] Fletcher, N., Hollenberg, L., Smith, J., Tarnopolsky, A. and Wolfe, J. (2006) “Vocal tract resonances and the sound of the Australian didjeridu (yidaki) II: Theory”, J. Acoust. Soc. America, 119, 1205-1213. (These papers have supporting web pages, with sound files, spectra and animations.)

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[8] Wolfe, J., Tarnopolsky, A.Z., Fletcher, N.H., Hollenberg, L.C.L. and Smith, J. (2003) “Some effects of the player’s vocal tract and tongue on wind instrument sound”. Proc. Stockholm Music Acoustics Conference (SMAC 03), (R. Bresin, ed) Stockholm, Sweden.
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6. Acknowledgements

This project was supported in parts by funding from the PVSF. We thank Ms. Emma Marriott for her editorial work and Mr. Mr. John Reid and Mr. Bill Chicione (Elleris, San Diego, CA, USA) for their technical support.

NOTE: The authors dedicate this work to the memory of Mr. Hyde, the father of the didgeridooperformer and the co-author of this paper, who passed away suddenly on February 6, 2012.