How we See How we Sound
"Voice is nothing but beaten air." A Roman politician named Seneca made this quote many years ago. Air is the "fuel" we need to power the voice; our vocal folds and vocal tracts chop up and shape this air into words. Without air, we could not speak or sing.
But we can't see air, so how can scientists and doctors measure voices, and why would they want to measure a voice anyway?
Suppose a person is having some trouble with his or her voice, for example it's too soft to hear well. The doctor may recommend some special exercises to strengthen the voice. Wouldn't it be helpful to have a measurement before starting the exercises, and then again, after a few weeks of the exercises to see if there has been improvement? These are called objective measures. In other words, the measurements are based on more than the doctor's or the patient's opinion that the voice sounds better after treatment.
There are now many interesting gizmos and tools that provide objective examinations of the voice. Here is a sample of those used today by scientists, doctors and speech-language pathologists.
This tool, abbreviated as EGG, measures how tightly the vocal folds are touching one another. This is an example of a non-invasive technique - no instrument enters the body. To do an EGG, two small disks are placed on either side of the neck. An mild electric current passes between the disks. The way the signal between the two disks behaves shows how much the vocal folds are in contact. [Remember, the vocal folds coming together creates voice.] The screen of the EGG displays the signal. The more the tissues are in contact, the higher the peaks. Do you also see some "valleys"? These represent times when the vocal folds were separated. Likely, the person in the photograph was breathing in air at that moment.
Because the our sound-producing organ, the larynx, is buried in the neck, it isn't easy for doctors and scientists to watch it do its work. Most of our organs, such as the heart or brain, are also buried deep within the body, and for this reason, experts have worked hard to develop imaging machines that allow us to visualize organs within the body.
One of oldest imaging technologies is x-ray. However, x-ray is of limited use in studying vocal structures. Can you guess why? X-ray is helpful in studying problems with bones of the body (for example, a break), but most vocal anatomy is soft tissue. Only a single bone - the hyoid - is part of the larynx. Other, newer imaging machines, such as the CT (computed tomography) and MRI (magnetic resonance imaging), can give us pictures of the soft tissues of the body. Within the last few years it has become possible not only to look at CT or MRI images in two dimensions, but also to create three-dimensional images of a person's vocal structures.
In a fascinating set of studies, Dr. Brad Story imaged the vocal system using MRI and CT.
Look at the result of his work (above). The subject was saying "ah" (as in the word, "hot") using an MRI. A sophisticated computer and special software allowed Dr. Story to manipulate the original MRI images after the scans were complete. In the photo, Dr. Story was able to divide the head and neck tissues, leaving the air space of the vocal tract (as shown in the center of the picture). Studying exact shapes such as these, Dr. Story and his colleagues can get an accurate understanding of how the body produces many sounds, such as "ah" and other vowels.
Without the help of videostroboscopy, doctors would not be able to see the human vocal folds at work. It is an often-used and important tool used by ear, nose and throat doctors (otolaryngologists) for their patients with voice problems.
Although it's a frighteningly long word, the procedure is simple. A doctor puts a steel rod between the lips and over the tongue, so that the tip is near the back of the throat. A miniature video camera, light, and magnifier are on the tip of the rod. With the tool in correct position, the doctor can see on an attached monitor the vocal folds moving. The machine also makes a video recording of the procedure to add to the patient's medical record.
A "strobe" light (yes, like the ones you see at school dances) is used to average quick vibrations of the vocal fold cycles. This slows the movement so the doctor can see the vocal folds while the patient makes easy sounds - usually an "eeeeeeee". With this powerful tool, the doctor can make many observations:
- Is the color of the inside of the larynx healthy? These tissues are fleshy-pink normally, but irritated tissues are often bright red. Does the patient have any growths or bumps that may be a sign of injury or disease that interfere with speaking normally? Are the left and right vocal folds the same shape and size? [If they differ greatly, it could explain a rough sounding voice.] Do they come together well, or are there gaps (which would leak air and give the voice a breathy sound)?
- Do the vocal folds vibrate in a healthy, predictable pattern?
Vocal Range Profile
A vocal range profile, sometimes called the phonetogram, is like playing a computer game with your voice. It's a tool used to determine the upper and lower limits of both your pitch range and loudness. Because every person's voice is different, everyone's VRP is unique; some scientists call it a "voice print" (the same idea that every person's fingerprint is unique). The VRP is really just a computer loaded with specially-written software and equipped with a microphone. To make a voice print, the user sits in front of the computer (ideally, in a sound-proof room), saying "ahhh" over and over at various pitches and loudnesses. The computer "draws" on the monitor the sounds of the user's voice. Look at the VRP in the photo. Pitch (frequency) is measured from left to right, with the lowest-pitched notes at the far left. Loudness (intensity) is measured from bottom to top, with the softest sounds near the bottom. When pitch and loudness are graphed together, the shape is often like a football. Notice that the user is more limited in how loud or soft she can be when she is vocalizing near the limits of her high and low pitches. In the comfortable "middle" of the pitch range, she is able to produce a wide range of loud and soft sounds.
Test your understanding of VPRs with a matching game.
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