AMAZINGLY FLEXIBLE, the human voice creates sounds as rich and complex as those of conventional musical instrumentsbut with much smaller equipment.
Image: AARON GOODMAN
In Brief
- Although the human vocal system is small, it manages to create sounds as varied and beautiful as those produced by a variety of musical instruments.
- All instruments have a sound source, a resonator that reinforces the basic sound and a radiator that transmits the sound to listeners.
- A human’s sound source is the vibrating vocal folds of the larynx; the resonator is the sound-boosting airway above the larynx; and the radiator is the opening at the mouth.
- The human voice can create such an impressive array of sounds because it relies on nonlinear effects, in which small inputs yield surprisingly large outputs.
-- The Editors
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How Instruments Make Music
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Sound Clips: The Human Instrument
The human vocal system would not receive much acclaim if instrument makers placed it in a lineup of traditional orchestral instruments. Arranged by size, for example, the voice box (larynx)—and the airway it sits in—would be grouped with the piccolo, among the smallest of mechanical music makers. And yet experienced singers compete well with all man-made instruments, one on one and even paired with full orchestras. Recent investigations of how our singing voice generates a remarkable range of sounds have revealed surprising complexity in the behavior of the vocal system’s elements and in the ways they interact.
For more than half a century, scientists explained the voice’s ability to create song by invoking a so-called linear theory of speech acoustics, whereby the source of sound and the resonator of sound (or amplifier) work independently. Researchers have now learned, however, that nonlinear interactions—those in which source and resonator feed off each other—play an unexpectedly crucial role in generating human sound. Such insights now make it possible to describe how great singers produce those amazing sounds.
This article was originally published with the title The Human Instrument.
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19 Comments
Add Commenthow are we a instrument.
Reply | Report Abuse | Link to this[b]The Human Instrument by Ingo R. Titze[/b]
Reply | Report Abuse | Link to this"But how can this complex tissue be kept in vibration when it cannot be bowed or repeatedly plucked inside the larynx? [i]The only source of energy available to deform the folds and thereby induce vibrationthe way that wind passing across a flag makes it flapis air flowing from the lungs.[/i] "(excerpt from The Human Instrument : Scientific American, January 2008 p.3 of article)
I must compliment the description of the anatomy of the vocal process that the author provides in the article The Human Instrument . However the assumption that the vocal cords can only activate in airflow is the same that I studied in vocal pedagogy more than thirty years ago. Let me suggest an alternative sound activation process that I have observed that is not considered in the article.
My expertise in this area is as a professional performing artist since 1951 with credits on Broadway, Opera, Recording, and Concert in classical, popular, and religious music; and as an instructor of the voice since 1972. I have also had the privilege of studying voice with Franco Iglesias (Placido Domingos voice teacher), had master classes with many other great singers including Luciano Pavarotti, Beverly Sills, Carlo Bergonzi, and been mentored by Jerome Hines, Franco Corelli, to mention a few. A short resume can be found on my website [url http://www.singingworld.com]www.SingingWorld.com[/url] for more documentation.
The suggestion of the article that the vocal cords must have airflow in order to produce sound is inaccurate.
Observing the anatomical structure of the vocal process intrinsically (inside myself), the vocal cords originate on the inside of the front of the Thyroid Cartilage and are hinged together there. The vocal cords then attach each on separate hinged cartilages called the Arytenoid Cartilages that are on the back top of the Cricoid Cartilage. The Arytenoids and the musculature that activate them open and close the vocal cords in the back.
A simple example of how the vocal cords open and close is that they function exactly like the hands open and close in clapping action when the tips of the fingers are held together. Just opening and closing the vocal cords even without airflow will cause an audible popping sound. [b]So a viable alternative to the article's assumption of airflow causing the vocal process to operate is that the vocal process claps, with infinite capability with or without airflow.[/b]
Sustained vocalization does require airflow, but that airflow can be either in or out. Singing is vocalization produced with in breath or inspiration. Vocalization on inspiration is what happens when one calls or beckons to another at a distance. This is the quality that singers use to sing most beautifully. Vocalization with an out breath or expiration is harsh and forbidding, and is found in a shout or scream which forces air out and is always an instinct warning intending all listeners to flee. In singing the out breath is used primarily for making consonants. Both of these vocalizations are reflexive in nature as is the operation of the voice and all of the breath.
Inspiration is the breath function most beneficial to singing beautifully. Instinctively the voice knows how to make all the sounds it is capable of making. Learning to recognize and control that instinct is the goal of studying the voice.
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Edited by Leslie at 01/13/2008 8:25 PM
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Edited by Leslie at 01/13/2008 8:30 PM
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Edited by Leslie at 01/13/2008 8:31 PM
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Edited by Leslie at 01/13/2008 8:33 PM
What mechanism is changed when the gas medium is changed as when one breathes helium? What in helium is responsible for the higher-pitched voice?
Reply | Report Abuse | Link to thisYou ask if the human is an instrument. We may be the instrument of many things including music and singing particularly. Especially singing as singing along with whistling and dancing and clapping is something that any of us can do to express our emotions pleasantly.
Reply | Report Abuse | Link to thisLeslie
> What mechanism is changed when the gas medium is
Reply | Report Abuse | Link to this> changed as when one breathes helium? What in helium
> is responsible for the higher-pitched voice?
There is no change in the mechanism, what is changed that causes the higher pitch is the lighter weight of the gas, thus the pitch is higher.
Leslie
I have regular singing lessons and have bought many books on singing structure and technique. Your article was a breath of fresh air, excuse the pun. Succinct and clear explanations, which are far superior to all the books I have bought put together.
Reply | Report Abuse | Link to thisHigher pitch causes by breathing Helium is down to Helium's [i]Bulk Modulus[/i], i.e. its compressibilty.
Reply | Report Abuse | Link to thisHelium breathing does not change the frequency of your voice! The frequency is determined by the oscillations of the vocal folds, which depend on their mass and muscular tension; the nature of the air around them contributes very little. However, because the speed of sound is higher in helium than in air (due to the lower density of helium; the bulk modulus is pretty much the same as for air), your vocal tract has high frequency resonances. This in turn means that the vocal tract will amplify the higher frequencies in the voice than before. But it doesn't raise the frequencies.
Reply | Report Abuse | Link to thisThe effect is like turning up the treble knob on your stereo: you can hear the flutes better, but Beethoven's Fifth Symphony is still in C minor.
When people say that the pitch rises when you breathe helium, they refer to the fact that the sound seems higher. But this is a psychological judgement. Pitch is related primarily to frequency; but it also depends (much less) on the spectrum of the sound (which is the situation for healium speech) and on loudness.
The word "pitch" is often used by musicians as a synonym of "frequency." But those who study hearing are aware that "pitch" (that is, how high a sound seems) is not exactly the same as frequency.
I do the following demonstration in my physics of music class. I sing the lowest note I can; then repeat it, after breathing helium. The note is clearly no higher, although the spectrum has changed so as to emphasize higher frequencies.
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Edited by horncabbage at 01/17/2008 3:47 PM
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Edited by horncabbage at 01/17/2008 3:48 PM
This is a response to Leslie's comments on the article: The Human Instrument.
The suggestion of the article that the vocal cords must have airflow in order to produce sound is inaccurate.
I am sorry to disagree with you, but Titze is in fact correct. When you close the vocal folds, they are essentials functioning as a valve. When this occurs, as the human body does not exist in a vacuum, there is immediately a change in pressure caused. You will not be able to observe a sound when you actually close the folds, but rather when you open then and the air pressure equalizes and the air flows through them and equalizes. Sure the closing of the valve may cause a displacement of molecules (a slight vibration), the actual intensity of said event is not perceivable by humans without the help of extremely precise equipment and therefore I would call into question if it would be called sound.
In your description of the hands together, the function you are describing, is also creating a flow of air over your palms, hence the sound.
As for your description of the "in breath" and "inspiration" and it being critical to singing. I think you are confused, there is the italian bel canto singing concept of inspirazione, in which the singer visualizes a sensation of inhalation as they sing, and will most likely feel a sensation that is quite similar to this. Some teachers also refer to this as drinking in the sound, or I believe in Jerry Hine's book Great Singers on Great Singing, this is what Pavarotti was describing when he spoke of smothering the sound. It is a visualization tool used by singers and teachers to help create the optimal exhalation, efficiency of the breath, and correct coordination of the vocal apparatus. It is not in fact occurring, you are not actually inhaling. However I believe the point of this article was to describe scientifically and accurately what is occurring during the process of singing.
Reply | Report Abuse | Link to thisSinging on the gesture of inhalation is a great illusion in singing. When a correct vowel/pitch combination is attained and vocal tract inertance is at work, the system is receiving feedback in the air column. There IS a real sensation of "drinking in the sound" but this is NOT actually happening, and this must not be mistaken for reality, nor taught to students. Trying to hold back air will only complicate matters. The right vowel/pitch combination with solve the problem and the singer will experience the sensations they need to replicate and improve their singing. The old masters were right, but be careful not to take imagery literally!
Reply | Report Abuse | Link to thisFrom a point of view of fluid mechanics, Author’s description of the movement of the air column is incorrect. See following paragraph:
Reply | Report Abuse | Link to this“When elastic recoil springs the folds back from the walls to close the glottis, the flow of air through the glottis subsides. Because of inertia, though, the air column continues to move up, leaving a partial vacuum in and above the glottis that acts to slam the folds more strongly together.â€
The air flow inside the vocal tract can be modeled with the Darcy-Weisbach’s law:
dP = f * (L/D) * V*V/2 * g (1) 
where,
dP is the pressure difference between the pressures in the vocal tract and the atmosphere. (dP = P – Patm)
gï€ is the density of the air
V is the velocity of the air molecular
L is the length of the vocal tract
D is the effective diameter of the vocal tract
And f is the friction factor, which is related to the smoothness of the inner surface of the vocal tract.
Due to the fact of g, L, D, and f can be treated as constants, for a specific singer singing a specific vowel, equation (1) can be simplified as
V = C* sqrt(dP) (2)ï€
equation (2) shows that the velocity of the air molecular is proportional to the square root of the pressure difference.
When elastic recoil springs the folds back from the walls to close the glottis, the pressure difference reduces, since there is no new air comes in. When the pressure difference reaches to zero, the velocity of the air molecular is also zero according to equation (2), therefore, P=Patm. That is, the minimum pressure above the glottis will be the pressure of the atmosphere, which will never be partial vacuum.
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Edited by DCheng at 02/13/2008 4:49 PM
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Edited by DCheng at 02/13/2008 4:51 PM
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Edited by DCheng at 02/13/2008 4:53 PM
Fascinating. As a professional opera singer and former physicist, I have always been troubled by how the vocal folds and vocal tract interact.
Reply | Report Abuse | Link to thisComparisons with other instruments are instructive but do not answer all questions. After all, there is a fundamental difference between the voice and wind instruments. With all wind instruments - using lips, reeds or edge tones as a source of vibration - the frequency is dictated by the length of the resonator whereas with the voice that is fixed. It is the cords that dictate the frequency - this is much more like the behaviour of stringed instruments. With the voice therefore the resonator, with its fixed length, has to respond well through a large range of frequencies. The idea that inertive reactance can modify the frequency at which a resonator will resonate is new to me. I would love to know more. It seems to me the article covers the anatomical aspects of how the voice produces its large range more thoroughly than the physical.
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Edited by Christopher at 02/17/2008 3:27 PM
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Edited by Christopher at 02/17/2008 3:30 PM
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Reply | Report Abuse | Link to thisDCheng is wrong I am afraid.
Reply | Report Abuse | Link to thisIt is clear that what Mr.Titze is talking about is tone instead of noise, or it is vowel. The glottis is closing completely after each opening. In this case, the air above the glottis is not stable, the velocity of the air moleculars is always changing. From a point of view of fluid mechanics, the Darcy-Weisbach equation is only valid for sheady flow. Because of the inertia of air, it is quite understandable that the minimum pressure above the glottis can be lower than the pressure of the atmosphere, which is partial vacuum. Mr.Titze is correct
Remember that fluid mechanics is a useful model for explaining sustained vocal fold oscillation, however the process is nonlinear. Even in speech, SOME nonlinear effects are taking place. If you look at inverse filtering you will never see a glottal pulse that isn't somewhat skewed to the right. If there were absolutely no interaction, the pulse would be symmetrical. In singing the nonlinear interaction is stronger. (There is a reverse flow back into the glottal source, and likely some from the trachea as well) This combined with the overshoot caused by inertia is likely the phenomenon that Titze is talking about. There are no standard equations(to my knowledge) that state the whole process mathematically.
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Thanks, interesting article, but I was looking for the one on vocal cords that appeared in SciAm in the 90s. How can I get my hands on that one?
Reply | Report Abuse | Link to thisThe human voice consists of sound made by a human being using the vocal folds for talking, singing, laughing, crying, screaming, etc. Its frequency ranges from about 60 to 7000 Hz. The human voice is specifically that part of human sound production in which the vocal folds (vocal cords) are the primary sound source. Generally speaking, the mechanism for generating the human voice can be subdivided into three parts; the lungs, the vocal folds within the larynx, and the articulators.
Reply | Report Abuse | Link to thisThe person conversation contains sound made by a personal using the songs breaks for talking about, performing, kidding, screaming, shouting, etc. Its frequency ranges from about 60 to 7000 Hz. The person conversation is specifically that part of personal sound development in which the songs breaks (vocal cords) are the primary sound source. In most cases, the process for making the personal conversation can be separated into three parts; the breathing, the songs breaks within the larynx, and the articulators.
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