TMH-QPSR, KTH, Vol. 46, 2004
Voice source characteristics in different
registers in classically trained female musical
theatre singers
Eva Björkner12, Johan Sundberg1, Tom Cleveland3 and Ed Stone3
1
Department of Speech Music Hearing, KTH, Stockholm, Sweden
Laboratory of Acoustics and Audio Signal Processing, Helsinki University of Technology, Finland
3
Vanderbilt Voice Center, Dept. of Otolaryngology, Vanderbilt Univ. Medical Center, Nashville, TN
2
Abstract
Musical theatre singing typically requires females to use two vocal registers.
Physiological differences between these registers, however, have not been
explicated. Our investigation considered voice source and subglottal pressure Ps
characteristics of these registers, here referred to as chest and head register. These
were studied by inverse filtering the oral airflow recorded for a sequence of /pae/
syllables sung at constant pitch and decreasing vocal loudness in each register by
seven female professional musical theatre singers. Ten equidistantly spaced Ps
values were selected and the relationships between Ps and several parameters were
examined; closed quotient Qclosed, peak-to-peak pulse amplitude Up-t-p, negative
peak of the differentiated flow glottogram, i.e., the maximum flow declination rate
(MFDR) and the normalised amplitude quotient (NAQ) [Up-t-p/ (T0*MFDR)] where
T0 is the fundamental period. Ps was typically slightly higher in chest than in head
register. As Ps influences the measured glottogram parameters, these were also
compared at an identical Ps of 11 cm H2O. Results showed that for typical tokens
MFDR and Qclosed were significantly greater while NAQ and Up-t-p were
significantly lower in chest than in head. These observations can be explained if
vocal fold thickness is assumed to be greater in chest register.
1. Introduction
According to Titze (1994) “The term register
has been used to describe perceptually distinct
regions of vocal quality that can be maintained
over some ranges of pitch and loudness”. Vocal
register is a phenomenon of great relevance in
vocal art, particularly in female singing. An
important task in singing training, regardless of
style, is to teach the student how to master the
transition from one register to the other with
minimal timbral changes. The register used in
the lower part of the female pitch range is
generally referred to as chest or modal, and the
register used in the adjacent higher part as head
or middle, henceforth chest and head register,
respectively. The transition between these
registers occurs somewhere between the pitches
of C4 and A4 (264 Hz and 440 Hz)(Sundberg &
Kullberg, 1999).
It is generally agreed that vocal registers
reflect voice source characteristics such as the
relative duration of the closed phase Qclosed, the
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TMH-QPSR, KTH, Vol. 46: 1-11, 2004
peak-to-peak pulse amplitude Up-t-p, and the
negative peak of the differentiated flow glottogram, i.e., the maximum flow declination rate
(MFDR). All these parameters are heavily
influenced by two physiological voice control
parameters, subglottal pressure Ps and glottal
adduction. For example, with increased glottal
adduction Qclosed tends to increase, and Up-t-p
tends to decrease (Hertegård et al., 1989). Hence
it seems reasonable to analyse these parameters
in a study of vocal registers.
The so-called Normalised Amplitude
Quotient (NAQ) has been launched as a measure
of glottal adduction (Alku et al., 2002). It is
defined as the ratio between Up-t-p/(T0*MFDR).
In a one-singer subject investigation, NAQ was
found to correlate with the degree of perceived
phonatory pressedness (Sundberg et al., 2002).
The same study also showed that the NAQ
parameter differed between styles of singing.
In classical singing, mainly the head register
is used while in non-classical styles, like pop,
jazz and blues, chest is used more commonly.
1
Björkner E et al.: Voice source characteristics in different registers ....
The repertoire in musical theatre, on the other
hand, demands a perfect control of both
registers. In the education of musical theatre
singing, classical training is often considered a
recommendable platform. In this repertoire, high
subglottal pressures are typically used. Such
pressures are commonly assumed to jeopardise
vocal health. To find out to what extent and
under what conditions this is true, a better
description and knowledge of the register
function in female singing is needed. Such
knowledge should be valuable also to vocal
training and therapy. As a step towards this goal,
the present investigation studies the register
function in professional female musical theatre
singers by analysing their voice source characteristics, paying special attention to the influence
of subglottal pressure on these characteristics.
2. Material and Methods
2.1 Subjects and recording
Seven female musical theatre singers between
the ages of 17-43 years, all classically trained,
volunteered as subjects (Table 1).
Table 1. Singer subjects data, including the
pitches chosen.
Singer
Age
Years of
experience
Pitch chosen
chest
head
MAR
43
14
Eb4
Eb4
PAT
37
17
C4
C4
SUB
39
11
G4
G4
COX
29
10
E4
F4
CIE
25
12
E4
Eb4
JUL
39
25
F4
F4
AL
17
None
F4
F4
Their task was to sing a sequence of the
syllable /pae/ at a pitch where they could use
both chest and head register. This pitch varied
between C4 and G4 for different subjects. They
initiated the sequence at high lung volume and
at maximum degree of vocal loudness and
continued while gradually decreasing vocal
loudness. They were asked to perform this
sequence three times first in chest and then three
times in head register. The vowel /ae/ was
2
chosen since its high first formant adds to the
reliability of inverse filtering and the oral
pressure during the p-occlusion allows estimation of Ps.
The flow signal was recorded using the
Rothenberg mask, a specially designed pneumotachograph for capturing oral flow. The subject
held a plastic tube, inner diameter 4 mm, in the
corner of her mouth for recording oral pressure.
The audio signal outside the mask was recorded
from a microphone at a distance of 30 cm from
the lips. All these signals plus an EGG signal
(Glottal Enterprises) were recorded on a multichannel digital recorder [TEAC RD 180 PCM].
2.2 Analysis
The effect of Ps variation on the voice source
can be ideally analysed by examining glottal
parameters as a function of several equally
spaced Ps values. Therefore, for each subject and
register ten Ps-values were selected. These
values were gained by computing the singer’s
total Ps variation range in the three takes. This
range was divided by 9, thus yielding 10
equidistantly spaced ideal Ps values. The Ps
values closest to these ideal values were then
identified from the three takes and selected for
further analysis. The entire material thus consisted of a total of 140 samples, ten for each
register and singer, respectively.
Subject MAR produced emphatic /p/
explosions in her head register recordings, as
demonstrated by sharply peaked oral pressure
peaks (Hertegård et al., 1995). Following the
recommendation of Hertegård, the estimates of
Ps in these cases were taken from the discontinuity appearing in the initial part of the
pressure peak.
2.3 Listening test
Informal listening to the subjects’ samples
revealed that some subjects produced very small
timbre differences between the registers. Hence,
a computerised listening test (Judge, Svante
Granqvist) was run with a panel of three voice
experts. Their task was to rate along a visual
analogue scale how representative the various
280 sung samples (10 degrees of vocal loudness
x 2 registers, x 2 presentations of each sample)
were of chest and head register. The subjects
were presented with a visual analogue rating
scale on the computer display, where 0 marked
‘Chest’ and 1000 was marked ‘Head’ (Figure 1).
The program recorded all response settings.
TMH-QPSR, KTH, Vol. 46, 2004
Figure 1. The display of the Judge program
used for the listening test.
Figure 2 shows the standard deviations as
function of the ratings averaged across the three
raters. The standard deviations were highest in
the center of the scale, as expected. For some
singers, the chest and head register data are
gathered toward the left and right sides of the
graph, respectively, indicating that their chest
and head register samples were perceived as
clear examples of these registers. Other singers,
on the other hand, produced samples that
differed less clearly. For singers JUL and AL,
most chest register tones were perceived as head
register tones. Their data were discarded, as they
seemed of limited value to a study of voice
source differences between registers.
A total of 16% of the samples received mean
ratings in the interval 0 – 250 while 49% of the
samples received ratings in the interval 7501000. In other words, a considerably greater
number of samples sounded as sung in head than
in chest register. Given this bias it seemed
promising to analyse the most typical cases in
the first place. The 17 samples that received
ratings in the range of 0-250 were thus accepted
as ‘clear cases of chest register’ while the 17
samples that received the highest mean ratings
were considered as clear cases of head register.
2.4 Voice source analysis
Vocal registers are determined by the voice
source, the sound produced by the pulsating
transglottal airflow. This airflow can be
retrieved by inverse filtering the flow signal, i.e.,
by eliminating the contributions from the vocal
tract. Flow glottograms were obtained using the
DeCap custom-made program (S. Granqvist).
Because of the relatively high pitch, the inverse
filtering was sometimes difficult. In such cases,
the formant frequencies used for the inverse
filtering were checked by using them for
synthesising the vowel sound. For this purpose,
500
450
400
AL
CIE
COX
JUL
MAR
PAT
200
300
SUB
SD [mm]
350
300
250
200
150
100
50
0
0
100
400
500
600
700
800
900
1000
Mean rating [mm]
Figure 2. Standard deviations of the three experts’ register ratings as function of the averages of
these ratings. Symbols refer to singer subjects, and filled and open symbols pertain to chest and
head register, respectively.
Speech, Music and Hearing, KTH, Stockholm, Sweden
TMH-QPSR, KTH, Vol. 46: 1-11, 2004
3
Björkner E et al.: Voice source characteristics in different registers ....
the custom made MADDE synthesiser was used
(S. Granqvist) which produces the voice sound
resulting from a specified set of formant and
fundamental frequencies combined with a
standard source spectrum. The formant frequency values were adjusted such that a ripplefree closed phase was obtained in the flow
glottogram at the same time as the synthesized
voice timbre was similar to that of the singer’s
original.
From the resulting flow glottograms, period
time, Qclosed, Up-t-p and MFDR were measured. In
addition, the normalised ratio between pulse
amplitude and MFDR, i.e. NAQ was determined. As Ps significantly influences most of
these parameters (Sundberg et al., 2002) it
seemed relevant to examine their variation with
Ps for the two registers.
3. Results
3.1 Statistical analysis
A 2-way ANOVA was carried out for the clear
cases, with register and singer as factors, see
Table 2. Due to a technical problem three phonations of singer SUB`s recordings could not be
analysed and had to be discarded. While this did
not affect the overall analysis her data had to
excluded from the statistical analysis.
Table 2. Result of the ANOVA of the listening
test.
Univariate Analysis of Variance
Clear
Cases
Ps
Register s
Singer
s
Register* s
Singer
Qclosed
s
ns
ns
Up-t-p MFDR NAQ
s
s
ns
s
s
s
s
ns
ns
Univariate Analysis of Variance
All
Cases
Ps
Register s
Singer
s
Register* ns
Singer
Qclosed
s
ns
ns
Up-t-p MFDR NAQ
ns
s
ns
s = significant
n = non-significant
Significant with alpha = 0.05
4
ns
s
ns
s
s
ns
Results show register as highly significant
for all parameters. Factor singer was found to be
significant for Ps (p=0.01), Up-t-p (p=0.01) and
MFDR (p=0.03). For MFDR, a significant
interaction was also found between the two
factors register and singer (p=0.03).
A second 2-way ANOVA was carried out for
all parameters, again with register and singer as
factors. The results show that register was
highly significant for the parameters Ps, Qclosed
and NAQ, and singer was highly significant for
parameter Ps, Up-t-p, MFDR and NAQ. No
significant interaction between register and
singer was found for any parameter.
Post Hoc Tests were also carried out between
singers and Ps. Both Tukey´s test and LSD
showed that Ps -values for singer PAT differed
significantly from COX, CIE and MAR, who
showed no significant differences between each
other. This is not surprising since PAT´s Psvalues were notably lower for both registers.
3.2 Acoustic/aerodynamic analysis
Figure 3 illustrates the differences between the
registers in terms of the means across the 17
clear cases. The mean and SD of Ps were higher
for the chest register samples, which also had
higher Qclosed and NAQ means, and somewhat
higher Up-t-p. The MFDR values were more
negative in the chest register. Figure 4, showing
mean Ps values, calculated over each subject’s
10 Ps values in each register, show higher values
for chest than for head. This was true for all
subjects.
As Ps significantly affects glottal parameters
and differed between the registers, it is interesting to analyse the variation of these parameters
with Ps. Figure 5 (left) a illustrates the relationship between Ps and Qclosed. Clear register differences can be observed. Chest register phonations (filled symbols) tended to show higher
Qclosed values than head register phonations
(open symbols). Thus, Qclosed tended to be higher
in chest register even though the differences
were smaller at lower Ps-values.
The same relationship is illustrated also in
Figure 5 (right), showing the relationship between pressure and Qclosed, averaged across
subjects. Here pressure is given in terms of the
normalized excess pressure, henceforth PSEN,
defined as the ratio (Ps - Psthreshold)/Psthreshold
(Titze, 1992). The dashed curves represent an
approximation of the data points by means of a
power function (Sundberg et al., 1999). The
approximation reflects the Qclosed values reason-
TMH-QPSR, KTH, Vol. 46, 2004
Qclosed
Ps
Mean across clear cases
Mean across clear cases
Chest
Head
20
15
10
5
Up-t-p
45
0,14
40
0,12
Mean across cle ar ca ses
25
35
30
25
20
15
10
0,06
0,04
0,00
0
NAQ
MFDR
0
0,30
-50
0,25
Mea n a cross clear case s
Me an across cle ar cases
0,08
0,02
5
0
0,10
-100
-150
-200
-250
-300
-350
0,20
0,15
0,10
0,05
0,00
Figure 3. Means across singer subjects of the indicated parameters for the two registers. The means
were calculated for the clear cases only. The bars represent one standard deviation.
ably well, except for the lowest PSEN. The
registers differ clearly with respect to the
asymptote, reaching 25% and 20% in chest and
head registers, respectively. In addition, the
growth of Qclosed with increasing PSEN is quicker
in chest register. These findings strongly suggest
that a longer closed phase is typical of chest as
compared to head register.
20
Chest
Head
Ps [cmH2O]
15
10
5
0
MAR
PAT
SUB
COX
CIE
Figure 4. Singer subjects’ mean subglottal
pressures Ps for the two registers.
Speech, Music and Hearing, KTH, Stockholm, Sweden
TMH-QPSR, KTH, Vol. 46: 1-11, 2004
The relationship between Ps and the other
glottal parameters is illustrated in Figure 6. For
increasing Ps, MFDR became more strongly
negative in both registers (Figure 6, above). The
Up-t-p tended to increase with increasing Ps
(Figure 6, left); the intersubject scatter could
reflect interindividual differences, e.g., with
respect to vocal fold length. The statistical
analysis asserted a highly significant influence
between factor singer and parameters MFDR
and Up-t-p.
Figure 6 (right) illustrates the relationship
between NAQ and Ps. The general trend is that
NAQ decreased with increasing Ps and that chest
register values were lower than head register
values. The statistical analysis showed that NAQ
was affected by register but was different
between singers.
As Ps heavily influences glottal parameters,
comparisons at identical Ps values are informative. All singers had used a Ps value of 11 cm
H2O, approximately, somewhere in their recording, except one who reached a maximum of 9
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Björkner E et al.: Voice source characteristics in different registers ....
MAR
Ps & QClosed
Mean Qclosed
PAT
50
30
SUB
COX
CIE
25
Q closed [%]
QClosed [%]
40
30
20
10
20
15
10
5
0
0
0
5
10
15
20
25
0
30
2
4
6
8
10
12
Normalised Excess Pressure
Pressure [cmH2O]
Figure 5. Closed quotient Qclosed as function of subglottal pressure Ps (left panel) and normalised
excess pressure (right panel). Filled and open symbols refer to chest and head register,
respectively. The right panel shows the mean values for all subjects and the dotted and dashed
curves represent the power function that best approximates these data points.
Ps & MFDR
0
MAR
PAT
SUB
COX
CIE
-100
MFDR
-200
-300
-400
-500
-600
0
5
10
15
20
25
30
Press ure [cmH2O]
Ps & NAQ
Ps vs. Up-t-p
0,40
NAQ
Up-t-p [arb unit]
0,30
0,20
0,10
0,00
0
5
10
15
20
Pressure [cmH2O]
25
30
0
5
10
15
20
Pressure [cmH2O]
25
30
Figure 6. The derivative MFDR, the flow amplitude Up-t-p and the NAQ as function of subglottal
pressure Ps for the five singers’ ten examples of chest and head register (filled and open symbols,
respectively).
6
TMH-QPSR, KTH, Vol. 46, 2004
250
chest
head
b
a
200
M FDR
-20
-30
-40
150
100
0,30
50
-50
MAR
COX
CIE
0
SUB
0,20
MAR
COX
CIE
SUB
0,15
0,10
30
c
25
20
15
10
5
d
Up-t-p [arb unit]
Qclosed [%]
e
0,25
NAQ
Sound level [dB]
-10
0,05
0,00
MAR
COX
CIE
SUB
0
MAR
COX
CIE
SUB
MAR
COX
CIE
SUB
Figure. 7. Sound level, Qclosed, Up-t-p, MFDR and NAQ for the singers’ phonations at a Ps of
11 cm H2O, approximately, in chest and head register.
cm H2O in head register. Productions at Ps =11
cm H2O in the two registers are compared with
regard to sound level and glottogram parameters
in Figures 7a - e.
Considering the random variation inherent in
the individual data points shown in the figure,
several surprisingly clear trends can be observed. Ps is the physiological control parameter
for vocal loudness and hence closely correlated
with sound level (Titze, 1994). On the other
hand, depending on various factors, such as
vocal fold morphology and pitch level, a given
Ps value will not produce the same sound
level in all voices (Titze, 1992). This variability
is illustrated in Figure 7a. For all subjects, sound
level was higher in chest. This appears to agree
with the typical observation that head register at
low fundamental frequency, henceforth F0, is
difficult to combine with loud phonation. Figure
7b shows that the higher sound level in chest
corresponded to a more negative MFDR in all
cases except in subject COX, probably depending on her dominant fundamental in head
register. The closed phase was clearly longer in
chest (Figure 7c). This should produce a strong
second partial. At the pitches used, this partial is
close to F1, so a stronger second partial will
enhance F1, which therefore contributes more to
the overall sound level in chest than in head.
Thus, the relationship between Ps and sound
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TMH-QPSR, KTH, Vol. 46: 1-11, 2004
level is complicated by a number of factors,
including register.
While Up-t-p did not differ consistently
between the registers and varied among singers,
(Figure 7d), NAQ was consistently lower in
chest than in head.
Summarising, the Ps difference between the
registers cannot account for all of the differences
illustrated in Figure 3, since the differences in
Qclosed and NAQ remained even under conditions
of an identical Ps value.
Of the glottogram parameters analysed, NAQ
seems particularly interesting. It represents a
ratio between MFDR, a parameter directly
depending on Ps, and Up-t-p, a parameter directly
dependent upon glottal adduction. A more
detailed analysis of the dependence of NAQ on
various glottal control parameters therefore
seemed relevant.
The different panels in Figure 8 illustrate the
relationship between NAQ and the different
parameters analysed. In general, the NAQ
values for head are higher than those for chest
register, as expected. Disregarding the considerable scatter it can be noted that small values of
Ps, Qclosed, and Up-t-p, and MFDR values close to
zero cause a great variation of NAQ. Thus, the
dependence of NAQ on Ps, Qclosed, Up-t-p, and
MFDR is almost nil at high values of these
parameters. Yet, NAQ tends to be greater in
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Björkner E et al.: Voice source characteristics in different registers ....
0,40
0,40
MAR
0,35
0,35
PAT
SUB
0,30
0,30
CIE
0,25
NAQ
NAQ
COX
0,25
0,20
0,20
0,15
0,15
0,10
0,10
0,05
0,05
0
5
10
15
20
25
30
0
10
20
30
Qclosed [%]
0,40
0,40
0,35
0,35
0,30
0,30
0,25
0,25
NAQ
NAQ
Pressure [cmH2O]
0,20
0,15
0,10
0,10
Up-t-p [arb unit]
50
0,20
0,15
0,05
40
0,05
-600
-500
-400
-300
MFDR
-200
-100
0
Figure 8. Relationship between NAQ and the indicated parameters. Filled and open symbols refer to
chest and head register.
head than in chest also in this range. This
indicates that the NAQ best reflects the
differences between the registers when produced
at loud phonation. Interestingly, the listening
test showed that chest and head phonation
differed most clearly in loud phonation.
As all singers did not use the same F0, it is
relevant to ask to what extent F0 affects NAQ.
For this purpose it seemed worthwhile to
examine also the non-normalised amplitude
quotient AQ, defined as
AQ = Up-t-p /(MFDR)
Figure 9 a-d shows NAQ and AQ as
functions of MFDR for the singers’ head and
chest register phonations. The scatter of the AQ
data is somewhat lower than for NAQ data. This
suggests that part of the NAQ variation between
singers may be caused by their differing F0
values. On the other hand, the NAQ differences
between registers within singers cannot be
explained in the same manner, since the
individual singer used the same F0 for both
registers.
4. Discussion
Inverse filtering is known as a risky method
under many experimental conditions, e.g., in the
8
absence of a clear closed phase, typical of soft
phonation. Several precautions were taken to
optimise measurement reliability, and our results
showed a systematic variation with Ps that was
similar to that found under more ideal experimental conditions. This suggests that our data
were reasonably reliable.
The availability of several Ps values seems a
strong advantage, providing heavy support for
the observation that Ps influences a number of
flow glottogram characteristics. For example,
the variation of Qclosed with Ps was similar to that
found for professional male singers, and can be
approximated by a power function (Sundberg et
al., 1999). However, our data for softest phonation deviated substantially from the power function. It is possible that this reflects an increased
glottal adduction in the softest phonations made
in order to add some timbral richness.
The Ps values were collected by asking the
subjects to sing a repeated /pae/ syllable with
continuously decreasing vocal loudness. This
implies that all loud phonations were produced
at higher lung volumes than softer phonations.
For untrained voices, this would be a source of
error, since glottal adduction tends to be lower at
high than at low lung volumes (Iwarsson et al.,
1998). For singers, on the other hand, the voice
TMH-QPSR, KTH, Vol. 46, 2004
HEAD
0,0012
0,30
0,20
0,0008
AQ
NAQ
HEAD
0,40
MAR
PAT
SUB
COX
CIE
0,0004
0,10
0,00
-600
-500
-400
-300
MFDR
-200
-100
0,0000
0
CHEST
-600
-500
-400
-300
MFDR
-200
-100
0
CHEST
0,40
0,0012
0,20
AQ
NAQ
0,30
0,0008
0,0004
0,10
0,00
-600
-500
-400
-300
-200
-100
0
MFDR
0
-600
-500
-400
-300
-200
-100
0
MFDR
Figure 9. NAQ and AQ values for chest and head register as function of the MFDR derivative.
Symbols refer to subjects.
source seems to be unaffected by lung volume
(Thomasson, 2003).
As mentioned, the listening test showed that
no more than 16% of all sung vowels were
classified as clear chest register while 49% were
classified as clear head register. One possible
reason for this bias could be that it is difficult to
differentiate registers in this pitch range,
particularly in soft phonation. A contributing
factor may be that the subjects sang into a
pneumotachograph mask that attenuated the
higher spectrum components slightly. As chest
register typically had a longer closed phase than
head, strong higher spectrum overtones should
belong to the characteristics of chest register.
Attenuation of such overtones can therefore be
expected to reduce the timbral difference
between the registers.
The pitch chosen for the register samples
varied from C4 to G4 between the subjects. An
informal test suggested that the mean NAQ for
three subjects tended to change systematically
with the F0-values for E4, F4, and G4. Also, we
found that the non-normalised AQ value showed
less variation than the normalised NAQ,
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TMH-QPSR, KTH, Vol. 46: 1-11, 2004
suggesting that NAQ varies with F0. On the
other hand, these data originated from different
singers. The relationship between F0 and NAQ
can be better elucidated with a material where
NAQ is determined within subjects phonating at
different F0.
The NAQ tended to be lower for chest than
for head register. According to an earlier study
(Sundberg et al., 2002), NAQ reflects perceived
pressedness. This appears to suggest that chest
register phonation is perceived as more pressed
than head register and that glottal adduction is
firmer in chest register. While the former seems
quite plausible, the latter would need corroboration in terms of independent investigation of
the relationship between NAQ and glottal
adduction.
Our results suggest that modification of Ps
and possibly also of glottal adduction are needed
for changing from chest to head register or vice
versa. As female musical theatre singers use
both registers they would need a refined control
of both breathing and phonation muscles.
According to our observations, chest register
is characterised by a high Ps and a greater Qclosed
9
Björkner E et al.: Voice source characteristics in different registers ....
and by a lower Up-t-p and NAQ. In female
untrained voices’ chest register, Qclosed was
found to be higher than in head register
(Sundberg & Kullberg, 1999). In addition, the
flow glottogram waveform was more sinusoidal
and the fundamental more dominant in head
register. Comparing professional baritones’,
tenors’ and counter tenors’ modal and falsetto
registers Sundberg & Högset (2001) found that
Ps and Qclosed were higher, glottal leakage
smaller, and the fundamental was weaker in
chest register. These observations are compatible with or similar to the findings of the
present investigation. They suggest that much of
the voice source differences, between these
registers, can be explained if the vocal folds are
assumed to be thicker in the modal/chest
register. Thicker folds would be associated with
a longer phase lag between the upper and lower
margins of the vocal folds, which should cause a
more extended closed phase (Figure 10).
Air flow (arb. scale)
Thin folds
(falsetto register)
1
Upper edge
0.5
Lower edge
0
0
2
4
Time (ms)
6
8
Air flow (arb. scale)
Thick folds
(modal register)
1
Lower edge
0
0
2
4
Time (ms)
6
8
Figure 10. Schematical illustration of the
effect of vocal fold thickness on the glottal
area. Thick vocal folds imply a great phase
lag between the upper and lower layer of the
folds, such that the opening of the upper
layer is interrupted by closing of the lower
layer and the area waveform becomes
triangular in shape. For thin vocal folds, the
phase lag is small, and the area waveform is
more rounded. After Sundberg & Högset
(2001).
10
The chest and head register voice source in
female musical theatre singers differ in several
respects. In typical tokens of chest register Ps
and MFDR are higher, Qclosed is greater while
Up-t-p and NAQ are lower than in head register.
Register differences are perceptually clearer in
loud than in soft phonation. The results also
show that Ps has a strong influence on flow
glottogram parameters. As NAQ seems associated with degree of perceived phonatory
pressedness, the low NAQ values for chest
register suggests a more adducted phonation as
compared to head register. The observed voice
source differences can be explained if vocal fold
thickness is assumed to be greater in chest
register.
Acknowledgements
The authors are indebted to the singers for their
kind participation, to Paavo Alku for support
and valuable discussions, and to Mattias Heldner
for the statistical analysis. The experiment was
carried out at the Vanderbilt University Voice
Center, Dr Robert Ossoff, chairman.
This investigation is part of Eva Björkner’s
doctoral dissertation work, which is financially
supported by the European Community's Human
Potential Programme under contract HPRN-CT2002-00276 [HOARSE-network].
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Upper edge
0.5
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