A Word about Air and an Some Airs about Words

Frequency and Pitch      The fact that humans have actually walked on the airless Moon is amazing. In my fantasy, humans could survive on the moon without the assistance of space suits by sucking oxygen out of moon rocks. Such people, however, would be totally dependent upon sign language. This is not only because their mouths would be full of rocks, but also because there is no atmosphere on the moon to carry a sound wave. On Earth we have atmosphere and, hence, we have sound. We think, and communicate in words and sentences which are composed of units of sound. It's the air, then, that makes oral language possible. Let's look at this phenomenon and see how it basically works and how it effects speech and language when it doesn't. We will be looking at three aspects of sound in air: Frequency, Intensity and Phase. Frequency is the number of times per second (cycles per second) that a molecule of air bounces (oscillates) back and forth.      Frequency and Pitch: What happens when I speak? Does my vocal fold hit a molecule of air to send it rebounding off the back of my throat, ricocheting around my mouth a few times, and then hurdling out across the room until it strikes someone's ear? Fortunately, for good hygiene, the answer is no. The action of the molecule is more like that of domino. You've heard of the "domino effect." This is where they line up a row of many dominos. When one is pushed over, it knocks the next one over in line, and so forth. You can watch the energy propagate itself along the line, although no domino moves farther then its length. There is one big difference. The domino just lies there, whereas a molecule of air bounces back like a ping pong ball. If the vocal folds are still moving, the molecule gets whacked repeatedly and bounces back again, and again and again. Count the number of times this happens each second and you have what is called, the frequency. We experience frequency as a range of Pitches from low (around 50 Hz) to high (around 20,000 Hz).   Of course, not one, but many molecules are involved, and as they hit the next molecule layer as a group, we have a band of compressed air, followed by a band of rarified air. This band expands in all directions like a balloon. And since the process is repeated, it is really more like an expanding balloon within a balloon within a balloon etc. Each balloon represents one cycle per second (cps).   Not that anybody calls it cycles per second anymore. In this age of high technology, that was too simple, so they changed it to Hz, in honor of a German physicist (Von Hertz). Oscillating is what the molecules of air are doing, and that is called Frequency. How we experience or perceive it is called Pitch. Our ears can detect a range of pitches from as low as 50 cps (excuse me, Hz) to around 20,000 Hz. Our most sensitive hearing is in the range of frequencies that speech sounds are produced.     Of course we don't hear each frequency equally well. The lower and higher frequencies require progressively louder sounds for us to hear. Our best hearing range for pitches is from around 400 Hz to about 5000 Hz. Happily, this is the same range at which speech sounds are generated! Were this not so we might all have to talk much louder to be understood. As we are all aware, speech sounds are divided into two groups--vowels, and consonants. But what we often don't think of is that as a group, vowels are low frequency sounds (extending a little above 1000 Hz); and consonants are high frequency sounds, (extending only a little below 1000 Hz). What makes this significant, is that consonants, taken as a group, are more important than vowels for speech intelligibility. Consonants are high frequency sounds that are critical to understanding speech.        Think about it, would you prefer to spend the rest of your life speaking only consonants or vowels? Here is a sentence with vowels only... "I oe ou a uera ay ai!" Here is a similar sentence in consonants only... "Wth cnsnts y cn lmst ndrstnd vr thng!" You will see the impact of this later when we discuss hearing and types of hearing loss. We will discuss a sensory neural (nerve) loss that often effects more radically the higher frequencies. Hence, babies can be born with a high frequency loss that would preclude their hearing consonants but not speech. These children would appear anything but deaf since they would respond to sounds, even soft ones (because of their low frequency components); but would not develop language or speech because they couldn't hear the consonants. A Pure Tone occurs when a molecule oscillates regularly and smoothly back and forth.  A single molecule oscillating up and down as a result of a noise would leave a tracing of its movement as a straight line.  If a more steady sound lasted for a second while I pulled the monitor screen to the left, the tracing of the movement of the molecule might look like this:  This is a description of how this molecule moves in time--smoothly and regularly (Periodic). This one would be called a Pure Tone. Tones have Periodic (regular) oscillations, but Noise has Aperiodic (irregular) movements    A Pure Tone is also called a Sine Wave, because of the shape of the curve of the movement. It is also called sometimes a Simple Tone, because it represents a Single Frequency. Hence, it is the smallest unit of sustained sound that one can have, as far as Tones are concerned. This, I suppose, means that there is another kind of sound other than a Tone. Yes, of course. You remember how we described the movement of a molecule for a tone as being regular? Well you can have oscillations that are not regular.  My wife says that this describes my dancing ability perfectly. Above it is a graphic representation of an Aperiodic sound It is called a Noise. Vowels are tones and originate in the larynx, whereas consonants are noises and are generated in the vocal tract.   A point of interest is that Vowels, which are sounds generated by the larynx, are Tones (although by no means Simple or Pure Tones). Consonants, on the other hand, which are sounds produced by constricting the air flow usually somewhere above the larynx (with the exception of /h/), are Noises.