The Acoustics of the
Singing voice
by Johan Sundberg March 1977
The voice organ is an instrument
consisting of a power supply (the
lungs), an oscillator (the vocal folds) and a resonator (the larynx, pharynx and
mouth). Singers adjust the resonator in special ways
Clearly
there is something quite unusual about the voice of a first class
opera singer. Quite apart from the music, the
intrinsic quality of such a voice
can have a forceful impact on the listener. Moreover,
a well-trained singer
produces sounds that can be heard distinctly in a
large opera house even over a
high level of sound from the orchestra, and can do so
week after week, year
after year. If a second-rate singer or a completely
untrained one tried to be heard
over an orchestra. the result would be a scream and
the singer's voice would
soon fail. Is it only training that makes the
difference? Or is the instrument that
produces an excellent singer's voice itself different
from other people's?
Let us begin with a description of that instrument. The voice organ
includes the lungs, the larynx, the pharynx, the nose and the mouth. The main
voice function of the lungs is to produce an excess of air pressure, thereby
generating an air stream. The air passes through the glottis, a space at,t he
base of the larynx between the two vocal folds (which are often called the
vocal cords but are actually elastic infoldings of the mucous membrane lining
the larynx). The front end of each vocal fold is attached to the thyroid
cartilage, or Adam's apple. The back end of each is attached to one of the
two small arytenoid cartilages, which are mobile, moving to separate the folds
(for breathing). to bring them together and to stretch them. The vocal folds
have a function apart from that of producing sound: they protect the lungs
from any small objects entrained in the inspired airstream. Just above the
vocal folds are the two "false" vocal folds, which are engaged when
someone holds his breath with an overpressure of air in the lungs. The vocal
folds are at the bottom of the tubeshaped larynx, which fits into the pharynx,
the wider cavity that leads from the mouth to the esophagus. The roof of the
pharynx is the velum, or soft palate, which in turn is the door to the nasal
cavity. When the velum is in its raised position (which is to say during the
sounding of all vowels except the nasalized ones), the passage to the nose is
closed and air moves out through the mouth.
The larynx, the pharynx and the mouth together constitute the vocal
tract, a resonant chamber something like the tube of a horn or the body of a
violin. The shape of the tract is determined by the positions of the articulators:
the lips, the jaw, the tongue and the larynx. Movements of the lips. jaw and
tongue constrict or dilate the vocal tract at certain sites: protruding the
lips or lowering the larynx increases the length of the tract.
Now consider the voice organ as a generator of voiced sounds. Functionally
the organ has three major units: a power supply (the lungs). an oscillator (the
vocal folds) and a resonator (the vocal tract). With the glottis closed and an airstream issuing from the lungs, the excess pressure below the glottis forces
the vocal folds apart: the air passing between the folds generates a Bernoulli
force that, along with the mechanical properties of the folds, almost immediately
closes the glottis. The pressure differential builds up again, forcing the vocal
folds apart again. The cycle of opening and closing, in which the vocal folds
act somewhat like the vibrating lips of a brass-instrument player. feeds a
train of air pulses into the vocal tract. The frequency of the vibration is
determined by the air pressure in the lungs and by the vocal folds' mechanical
properties. which are regulated by a large number of laryngeal muscles.
In general the higher the lung pressure is and the thinner and more
stretched the vocal folds are, the higher is the frequency at which the folds
vibrate and emit air pulses. The train of pulses produces a rapidly oscillating
air pressure in the vocal tract:
The sound generated by the airstream chopped by the
vibrating vocal
folds is called the voice source. It is in effect the
raw material for speech or
song. It is a complex tone composed of a fundamental
frequency (determined
by the vibratory frequency of the vocal folds) and a
large number of higher
harmonic partials, or overtones. The amplitude of the
partials decreases
uniformly with frequency at the rate of about 12 decibels
per octave. The
"source spectrum," or plot of amplitude
against frequency, for a singer is not
very different from that for a nonsinger, although the
spectrum does tend to
slope more steeply in soft speech than it does in soft
singing.
The vocal tract is a resonator, and the transmission of sound through an
acoustic resonator is highly dependent on frequency. Sounds of the resonance
frequencies peculiar to each resonator are less attenuated than other sounds
and are therefore radiated with a higher relative amplitude, or with a greater
relative loudness, than other sounds: the larger the frequency distance
between a sound and a resonance is, the more weakly the sound is radiated. The
vocal tract has four or five important resonances called formants. The many
voice-source partials fed into the vocal tract traverse it with varying success
depending on their frequency: the closer a partial is to a formant frequency.
the more its amplitude at the lip opening is increased. The presence of the
formants disrupts the uniformly sloping envelope of the voice-source spectrum,
imposing peaks at the formant frequencies. It is this perturbation of the
voice-source envelope that produces distinguishable speech sounds: particular
formant frequencies manifest themselves in the radiated spectrum as peaks in
the envelope, and those peaks are characteristic of particular sounds.
The formant frequencies are determined by the shape of the vocal tract.
If the vocal tract were a perfect cylinder closed at the glottis and open at
the lips and 17.5 centimeters (about seven inches) long, which is about right
for the average adult male, (then the first four formants would be close to 500,
1,500, 2,500 and 3,500 hertz (cycles per second). Given a longer or shorter
vocal tract, these basic frequencies are somewhat lower or higher. Each
formant is associated with a standing wave, that is, with a static pattern of
pressure oscillations whose amplitude is at a maximum at the glottal end and
near a minimum at the lip opening [see illustration
on page 19]. The lowest formant corresponds to a quarter of a wavelength.
which is to say that a quarter of its wavelength fits within the vocal tract.
Similarly, the second, third and fourth formants correspond respectively to
three-quarters of a wavelength, one and a quarter wavelengths and one and
three-quarters wavelengths.
Any change in the cross section of the vocal tract shifts the individual
formant frequencies, the direction of the shift depending on just where the
change in area falls along the standing wave. For example, constriction of the
vocal tract at a place where the standing wave of a formant exhibits
minimum-amplitude pressure oscillations generally causes the formant to drop in
frequency: expansion of the tract at those same places raises the frequency.
VOICE
ORGAN is composed of the lungs and the larynx, pharynx, mouth and nose, shown
in longitudinal section (top). The
larynx is a short tube at the base of which are twin infoldings of mucous
membrane, the vocal folds. The larynx opens into the pharynx; the opening Ls
protected during swallowing by the epiglottis. The larynx, pharynx and mouth
(and in nasal sounds also the nose) constitute the vocal tract It is a
resonator whose shape, which determines vowel sounds, is modified by changes in
the position of the articulators: the lips, the jaw, the tip and body of the
tongue and the larynx. The vocal folds, seen from above in a transverse section
(bottom), are opened for breathing and are closed for phonation by the pivoting arytenoid cartilages.
The
vocal tract is constricted and expanded in many rather complicated ways, and
constricting it in one place affects the frequency of all formants in different
ways. There are, however, three major tools for changing the shape of the tract
in such a way that the frequency of a particular formant is shifted in a
particular direction. These tools are the jaw, the body of the tongue and the
tip of the tongue. The jaw opening, which can constrict the tract toward the
glottal end and expand it toward the lip end, is decisive in particular for the
frequency of the first formant, which rises as the jaw is opened wider. The
second formant frequency is particularly sensitive to the shape of the body of
the tongue, the third-formant frequency to the position of the tip of the
tongue. Moving the various articulatory organs in different ways changes the
frequencies of the two lowest formants over a considerable range, which in
adult males averages approximately from 250 to 700 hertz for the first formant
and from 700 to 2,500 hertz for the second. Moving the articulatory organs is
what we do when we speak and sing: in effect we chew the standing waves of our
formants to change their frequencies. Each articulatory configuration corresponds
to a set of formant frequencies. which in turn is associated with a particular
vowel sound. More specifically, the formant frequencies enhance voice-source
partials of certain frequencies and thus manifest themselves as the peaks characterizing
the spectrum envelope of each vowel sound.
VOICE
ORGAN is composed functionally of a power supply, an oscillator and a
resonator. The airstream from the lungs is periodically interrupted by the
vibrating vocal folds. The resulting sound, the voice source, has a spectrum
(right) containing a large number of harmonic partials, the amplitude of which
decreases uniformly with frequency. The air column within the vocal tract has
characteristic modes of vibration, or resonances, called formants (A, B, C). As
the voice source moves through the vocal tract each partial is attenuated in
proportion to its distance from formant nearest it in frequency. The formant
frequencies thus appear as peaks in the spectrum of the sound radiated from the
lips; the peaks establish particular vowel sounds.
Al the elements and functions of the voice organ that
I have been describing are
common to singers and nonsingers alike. Do singers
bring still other faculties
into play or manipulate the voice instrument in
different ways? Let us begin by
comparing normal male speech and operatic singing.
Careful attention to a
singer's voice reveals a number of modest but very
characteristic deviations in
vowel quality from those of ordinary speech. For
example, the ee sound of a
word such as "beat" is shifted toward the
umlauted a of the German "fur"; the
short a of
"head" moves toward the vowel sound of "heard." The general
impression is that the quality of the voice is
"darker" in singing, somewhat as it
is when a person yawns and speaks at the same time;
voice teachers sometimes
describe the effect as "covering."
These shifts in vowel quality have been found to be associated with peculiarities
of articulation. In "covered" singing the larynx is lowered, and
X-ray pictures reveal that the change in the position of the larynx is
accompanied by an expansion of the lowest part of the pharynx and of the
laryngeal ventricle, the space between the true vocal folds and the false ones.
It is interesting to note that voice teachers tend to agree that the pharynx
should be widened in singing, and some of them mention the sensation of
yawning. In other words, a low larynx position and an expanded pharynx are
considered desirable in singing.
What we recognize as a darkened voice quality in singing is reflected
very clearly in the spectrum of a sung vowel sound. A comparison of the spectra
of the vowel in "who'd" as it is spoken and sung shows that the two
lowest formant frequencies are somewhat lower in the sung version and that the
spectral energy, or amplitude, is considerably higher between 2,500 and 3,000
hertz [see top illustration on page 21].
This spectral envelope peak is typical of all voiced sounds sung by
professional male singers. Indeed, its presence, regardless of the pitch, the
particular vowel and the dynamic level, has come to be considered a criterion
of quality: the extra peak has been designated the "singing formant."
What is the origin of the singing-formant peak? The peaks in the spectrum
envelope of a vowel normally stem. as I have explained, from the presence of
specific formants. The insertion of an extra formant between the normal third
and fourth formants would produce the kind of peak that is seen i4 the spectrum
of a sung vowel [see bottom illustration
on page 2l ]. Moreover, the acoustics of the vocal tract when the larynx is
lowered are compatible with the generation of just such an extra formant. It
can be calculated that if the area of the outlet of the larynx into the pharynx
is less than a sixth of the area of the cross section of the pharynx. then the
larynx is acoustically mismatched with the rest of the vocal tract: it has a
resonance frequency of its own, largely independent of the remainder of the
tract. The one-sixth condition is likely to be met when the larynx is lowered,
because the lowering tends to expand the bottom part of the pharynx. I have
estimated on the basis of X-ray pictures of a lowered larynx that this
lowered-larynx reson4nce frequency should be between 2,500 and 3,000 hertz.
that is, between the frequencies of the normal third and fourth formants and
just where the singing-formant peak appears. The lowering of the larynx. in
other words. seems to explain the singing-formant peak.
FORMANTS correspond to standing waves, or static patterns of air pressure
oscillations, in the vocal tract. Here the
first four formants
are shown as standing waves in cylindrical tubes, the
schematic
equivalent of the vocal tract (colored areas in drawings). The sine
waves represent the amplitude of the pressure
differential, which is
always maximal at the glottal end and minimal at the
lips. For the
lowest formant a quarter of a wavelength is within
the vocal tract
and, if the tract is 17.5- centimeters long, the
formant's frequency is
about 500 hertz (cycles per second). The second, third
and fourth
formants are 3/4, 5/4 and 7/4 of a wavelength, and
their frequencies
vary accordingly. If the area of the vocal tract is
decreased or
increased at a place where the formant's pressure
amplitude is at a
minimum (arrows),
that formant's frequency is respectively lowered
or raised; the same change in area has the opposite
effect if it is at
a pressure maximum.
MOVEMENT
OF ARTICULATORS [upper fig.] changes the cross section of the vocal tract,
shifting formant frequencies. Three articulatory configurations are shown
(top) together with the spectrum of the vowel sound produced by each; the
peaks in the spectrum envelope reflect the formant frequencies. The chart (bottom) gives the frequencies of the
first and second formants in some English vowel sounds as spoken by an average
male. For a female or a child the envelope pattern would be about the same but
the peaks would be shifted somewhat higher in frequency.
It also accounts for something else. Acoustically the expansion of the
lowermost part of the pharynx is equivalent to an increase in the length of
the vocal tract, and the lowering of the larylnx adds still more to the length.
The result is to shift downward all formant frequencies other than the
larynx-dependent extra formant. This lowering of frequency is particularly
notable in formants that depend primarily on the length of the pharynx. Two
examples of such formants are the second formant of the vowels in
"beat" and "head." and a drop in the frequency of those
formants moves their vowels respectively toward those of "fur" and "heard." The lowering of the larynx,
then, explains not only the singing-formant peak but also major differences in
the quality of vowels in speech and in singing.
To explain the singing formant's articulatory and
acoustic origin is not enough,
however. Why, one wonders, is it desirable for singers
to lower the larynx,
producing the singing formant and darkening the
quality of their vowels? A
plausible answer to the question has been found. It is
related to the acoustic
environment in which opera and concert singers have to
work: in competition
with an orchestra. Analysis of the average
distribution of energy in the sounds
of an opera or symphony orchestra shows that the
highest level of sound is in
the vicinity of 450 hertz: above that the amplitude
decreases sharply with
frequency. Now, normal speech develops maximum
average energy at about the
same frequency and weakens at higher frequencies. A
singer who produced
sounds with the energy distribution of ordinary
speech would therefore be in
trouble: the orchestra's much stronger sounds would
drown out the singer's. The
average sound distribution of a trained singer, on the
other hand, differs from
that of normal speech-and of an orchestra-mainly
because of the singing-
formant effect.
We have
shown that a singer's voice is heard much more easily
against recorded noise that has the same average
energy distribution as an
orchestra's sound if the voice has a singing formant.
Not only is the formant
almost invariably audible, because its frequency is in
a region where the orchestra's
sound is rather weak, but also it may help the
listener to "imagine" he
hears other parts of the singer's spectrum that are
in fact drowned out by the
orchestra.
The
singing formant is at an optimal frequency, high enough to be in the region of
declining orchestral-sound energy but not so high as to be beyond the range in
which the singer can exercise good control. Because it is generated by
resonance effects alone, it calls for no extra vocal effort: the singer
achieves audibility without having to generate extra air pressure. The singer
does pay a price. however, since the darkened vowel sounds deviate
considerably from what one hears in ordinary speech. In some kinds of singing
that price is too high: the ideas and moods expressed in a "pop"
singer's repertoire, for example, would probably not survive the deviations
from naturalness that are required to generate the singing formant. And pop
singers do not in fact darken their vowels: they depend on electronic amplification
to be heard.
In cartoons a female opera singer is almost invariably depicted as a fat
woman with her mouth opened very wide. In a study of female singers I have
found that the way in which the jaw is manipulated is in fact quite different
in ordinary speech and in singing. In speech the size of the jaw opening varies
with the particular vowel, but in female singing it tends to depend also on the
pitch of the tone that is being sung: the higher a soprano sings, the wider her
jaw is opened. This suggested to me that a soprano must vary the frequency of
her first formant according to the pitch at which she is singing. Analysis of
formant frequencies confirmed that the articulation was being varied in such
a way as to raise the first-formant frequency close to the frequency of the
fundamental of the tone being sung. I noted such a frequency match whenever the
frequency of the fundamental was higher than the frequency of a vowel's first
formant in ordinary speech.
VOWELS SOUND DIFFERENT in speech and in singing and the singer are
compared. What is significantly different about the sung difference is visible
in their recorded spectra. Here the spectra of the spectrum is the
spectral-energy peak that appears in it between about vowel in
"who'd" as spoken (left) and
as sung (right) by a male opera 2,500
and 3,000 hertz The new peak is called the singing formant.
SINGING
FORMANT'S ORIGIN (left) and its
utility in singing (right) are demonstrated. An extra formant was inserted
between the usual third and fourth formants in an experiment with an electronic
resonator that behaves like the vocal tract (left).
The new formant in. creased the amplitude of the partials near it by more
than 20 decibels; similarly, an extra formant (achieved by lowering the larynx)
supplies the high-frequency peak in the spectrum of a sung vowel. The three
curves (right) show the averaged distribution of energy in the sound of
orchestral music (black), of ordinary
speech (gray) and of the late tenor
Jussi Bjorling singing with an orchestra (colored).
The distribution is very similar for speech and the orchestra at all
frequencies; it is the singer's voice that produces the peak in the colored
curve between 2,000 and 3,000 hertz In that frequency region a singer's voice
is loud enough, compared with an orchestra's sound, to be discerned.
The reason becomes clear when one considers that the pitch frequency of
a soprano's tones is often much higher than the normal frequency of the first
formant in most vowels. If a soprano sang the vowel ee at the pitch of her middle C and with the articulation of
ordinary speech, her first formant would be in the neighborhood of 270 hertz
and the pitch frequency (the frequency of her lowest spectrum partial) would be
almost an octave higher. at 523 hertz. Since a sound is attenuated in proportion
to the distance of its frequency from a formant frequency, the fundamental
would suffer a serious loss of amplitude. The fundamental is the strongest
partial in the voice-source spectrum, and the higher its pitch is, the more
important the fundamental is for the loudness of the tone, and so the singer's ee would be rather faint. Assume that her next sound was the ah sound of "father," to be
sung at the pitch of high F. The fundamental, at 698 hertz, would be very close
to the frequency of the first formant, about 700 hertz, and so the tone would
be loud. The loudness of the singer's tones would vary, in other words,
according to a rather unmusical determinant: the frequency distance between
first formant and fundamental. In order to modulate the loudness according to
the musical context. the singer would need to continually vary her vocal
effort. That would strain her vocal folds. (Experiments with synthesized vowel
sounds suggest that it would also produce tones more characteristic of a mouse
under severe stress than of an opera singer!)
The soprano's solution is to move the first formant up in frequency to
match the frequency of the fundamental. thus allowing the formant always to
enhance the amplitude of the fundamental. The result is that there is minimal
variation in loudness from pitch to pitch and from vowel to vowel. Moreover,
changing the size of the jaw opening in this way provides maximum loudness at
the lowest possible cost in vocal effort. The strategy is probably resorted to
not only by sopranos but also by other singers whose pitch range includes
frequencies higher than those of the first formants of ordinary speech: contraltos,
tenors and occasionally even baritones.
It can be hard for a student of singing to learn this special way of
regulating the jaw opening, and particularly hard if the jaw muscles are under
constant tension. That may explain why many singing teachers try to get their
students to relax the jaw. Another frequent admonition is: "Hear the next
tone within yourself before you start to sing it." That could be
necessary because proper manipulation of the jaw opening requires some
preplanning of articulation for particular vowels and for the pitch at which
they are to be sung. Opening the jaw, however. is not the only way to raise the
first-formant frequency. Shortening the vocal tract by drawing back the
corners of the mouth serves the same purpose.. and that may be why some
teachers tell their students to smile when they sing high tones.
Since formant frequencies determine vowel quality,
shifting the first formant
frequency arbitrarily according to pitch might be
expected to produce a
distorted vowel sound, even an unintelligible one. It
does not have this effect.
largely because we are accustomed to hearing vowels
produced at various
pitches in the ordinary speech of men, women and
children with vocal tracts of
very different lengths: if a vowel is highpitched, we
associate it with relatively
high formant frequencies. The correlation is so well
established in our
perceptual system that we may perceive a change of
vowel when we hear two
sounds with identical formant frequencies but different
pitches: if a singer
raises her first-formant frequency with the pitch.
some of that rise is
actually required just to maintain the identity of the
vowel. It is true that
when the pitch is very high, our ability to identify
vowels deteriorates, but
that seems to be the case no matter what the formant
frequencies are.
The soprano. in other words, does not sacrifice much
vowel intelligibility
specifically as a result of her pitch-dependent choice
of first-formant
frequency. (Incidentally, composers of vocal music
are conscious of the
problem of vowel identification at high pitches and
generally avoid
presenting important bits of text only at the top of a
soprano's range:
often the text is repeated so that the words can be
well understood at a
lower pitch.)
It is clear that a good deal of the difference between spoken and sung
vowels can be explained by the singer's need for economy of vocal effort. The
general idea is the same, whether in being heard over the orchestra or in
maintaining loudness at high pitch: to take advantage of vocal-tract resonance
characteristics so as to amplify sounds. The importance of these resonances,
the formants, is paramount.
SOPRANOS
and other singers of high tones tend to open their mouth wider with rising
pitch. The tendency is demonstrated in these photographs of a soprano singing
the vowel sounds of ‘’heed’’ [top] and of ‘’who’d’’ [middle] at successively
higher pitches , shown in musical notation [ bottom]. When these photographs were made, the singer tract just as her own
voice source would have been but that was more held a vibrator against her neck
and a small microphone was placed near her lips. She began to sing each vowel
at a specified pitch then, with the
vibrator turned on, she stopped singing but maintained the positions of the
articulatory organs.
The
vibrator now supplied a steady, low-pitched sound that was influenced by the
singer’s vocal tract just as her own voice source would have been but that was
more suitable for analysis than a high voice tone, which has few partials.
Confirmation
of the importance of the formants was provided by a recent study of how male
voices are classified as bass. baritone or tenor. Obviously the singer's
frequency range is ultimately the determinant, but even when the true range
(which is established primarily by the shape. size and musculature of the vocal
folds) has not yet been developed. a good voice teacher can often predict the
classification after listening to a student's voice. How is that possible`
Thomas F. Cleveland. who was visiting our laboratory at the Royal Institute of
Technology in Stockholm and is now at the University of Southern California,
analyzed vowels sung by basses, baritones and tenors with respect to formant
frequencies and the spectrum of the voice source. Then he had a jury of voice
teachers listen to the vowel samples and classify the voices. The teachers
tended to classify vowels in which the formant frequencies were comparatively
low as having been sung by bass voices and vowels whose formant frequencies
were high as having been sung by tenors. Variations in the voice-source
spectrum (which varied slightly with the pitch at which a vowel was being
sung), on the other hand. did not provide a basis for consistent
classification. In a second test the same jury judged a series of synthesized
(and therefore clearly defined) sounds and confirmed Cleveland's original
impression: the lower the formant frequencies of a given vowel were, the lower
the singer's voice range was assumed to be.
Cleveland found that typical bass and tenor voices differ in formant:
frequencies very much as male and female voices do. The formant-frequency differences
between males and females are due mainly to vocal-tract length. and so the
bass-tenor differences are probably also largely explained by the same physical
fact. Formant frequencies are determined, however, not only by the individual's
vocal-tract morphology but also by habits of articulation. which are highly
variable. Be that as it may, vocaltract morphology must set limits to the
range of formant frequencies that are available to a singer.
FIRST FORMANT
A this point
the reader who knows and cares about music may be rather disappointed.I have failed to mention a number of factors that are
often cited as determinants of excellence in singing: the nasal cavity, head and
chest resonances, breathing and so on. These factors have not been mentioned simply because
they seem to be not relevant to the major acoustic properties of the vowel sounds
produced in professional operatic singing. Our research suggests that professional
quality can be achieved by means of a rather normal voice source and the resonances of the
vocal tract.
NEED
FOR WIDE JAW OPENING arises from the fact that a soprano must often sing tones
whose fundamental (lowest partial) is far higher in frequency than the normal
first formant of the vowel being sung. When that is the case (top), the amplitude of the fundamental
is not enhanced by the first formant and the sound is weak. Opening the jaw
wider raises the pitch of the first formant. When the first-formant frequency
is raised to match that of the fundamental (bottom),
the formant enhances the amplitude of the fundamental and the sound is
louder.
Our
implied model may not be perfect, to be sure. It is just possible, for example,
that the nasal cavity has a role in the singing of vowels that are normally
not nasalized. If that is so, we have attributed its effect to the voice
source, thus compensating for one error by making another. Moreover, we have
dealt only with sustained vowel sounds, whose production is important but is
certainly not the only acoustic event in singing.
Resonances outside the vocal tract. such as in the head or the chest,
cannot contribute appreciably to the singer's acoustic output in view of the
great extent to which sound is attenuated as it passes through tissues. This
is not to say that such resonances may not be important to the singer, who may
receive cues to his own performance not only from what he hears but also from
felt vibrations. As for breathing. it is clear that 'the vocal folds would
vibrate no matter by what technique an excess of air pressure is built up
below the glottis. Breathing and laryngeal manipulation are likely to be
physiologically interdependent. however, since the larynx is the gatekeeper of
the lungs. Probably different ways of breathing are associated with different adjustments
of the larynx. and probably some ways are effective for singing and others are
inadequate or impractical.
Finally we return to the original question: What is so special about a
singer's voice? The voice organ obeys the same acoustic laws in singing that it
does in ordinary speech. The radiated sound can be explained by the properties
of the voice-source spectrum and the formants in singing as in speech. From an
acoustical point of view singers appear to be ordinary people. It is true that
there is a major difference between the way formant frequencies are chosen in
speech and the way they are chosen in singing, and hence between the way vowels
are pronounced in singing and the way they are pronounced in speech. A man with
a wide pharynx and with a larynx that will resonate at a frequency of between
2,500 and 3,000 hertz is likely to be able to develop a good singing voice more
readily than a person who lacks those characteristics. And his progress may be
facilitated if his vocal folds give him a range that agrees with his formant
frequencies.
As for a female singer, she should be able to shift the first formant to
join the pitch frequency in the upper part of her range: that requirement may
bar some women with a long vocal tract from having a successful career as a coloratura
soprano. There are, in other words, a few morphological specifications that
probably have some effect on the ease with which someone can learn to sing
well. There are other conditions that may be more important, however. It is in
the complex of knowledge, talent and musical instinct that is summed up as
"musicality," rather than in the anatomy of the lungs and the vocal
tract, that an excellent singer's excellence lies.
end