Well welcome back to the third of these modules in the course, and this one is on vocalization and vocal tones. Now, I guess the first question you might ask is why are we talking about vocalizations and vocal tones? What's that have to do with music? And my answer would be, just about everything. And let me make some general points that head us in the right direction in that respect. So the first of these points would be that human vocalizations are really the major source of tonal sound signals in the environment we evolved in. So we ask, why do we have a sense of tonality in the first place? The answer would be, well, we have it, as I think I mentioned earlier in the course, we have it so that we can appreciate total sounds. And the total sounds that we most want to appreciate are human vocal sounds. Why is that? It's because these signals convey information about the size, the gender, the emotional state, and even individual identity of the speaker. Those are all biologically critical pieces of information, and it's not surprising that we would want to and have evolved the wherewithal to hear them. Thus, from a biological perspective, identifying human vocalizations is really critical. The last point, and this will come out not only today but in the subsequent modules, is that vocal tones and their appeal are very likely the forerunners of musical tones and why we like them so much. Lesson one concerns the production of vocal sound signals. If we're gonna talk about vocal tones, we certainly need to know something about the human vocal tract, and how they are produced. So let me introduce you to the human tract and just point out its essential features. So, the first aspect of the human vocal tract that you wanna know about is the vocal folds, or vocal cords, in the larynx. The larynx is here, underneath the Adam's apple that you can feel, and that's equivalent or similar to the flex strings of an instrument. The vocal chords vibrate, not exactly in the same way as the flex string that we talked about before, but in a generally similar way. And they're causing the vibration, the vibratory modes, that are generating the harmonic series that's essential to any tone. But the rest of the vocal tract is critically important as well. So the rest of the vocal tract includes the pharynx, the oral cavity here, the tongue, the movement of the tongue, the lips. All of these elements that you see anatomically here are considered part and parcel of the vocal tract, and they all have a decisive influence on the tones that come out of the mouth. They modulate the vibrations of the vocal chord in a way that allows us to produce and ultimately for the listener to hear, the vocal sounds that we're going to be talking about today. So, again, just In summary, the vocal tract begins with the vocal cords, but the vibration that's set up by the vocal cords is critically modulated by the rest of the vocal tract in a dynamic way that's under neural control and that has the wherewithal to produce the vocal sounds that we ultimately hear and that are the basis of language. So let's go through how that really works. Of course, you need a reservoir of air to push through the vocal cords, vocal folds, and make them vibrate, and that reservoir is the lungs. There air that rushes through the opening between the vocal chords here and here is called the glottis, and it's the tension of the vocal chords that determine the pitch of the sound that we hear. Again, this is under normal control. As you raise the pitch that you want to express in a vocal sound, the tension on the vocal chords increases. So what comes out, if you put a microphone at the level of the vocal chords here, what comes out is a harmonic series shown in this diagram that I've just circled. So that harmonic series of course, again, has a fundamental frequency and then a series of additional peaks of frequency that are multiples, integer multiples, of the fundamental frequency. What happens in the rest of the vocal tract, as I said, is equally critical. So these are the effects of the rest of the vocal tract. The pharynx, the oral cavity, and the position of the tongue, the lips, and the size of the space that's enclosed in all of that. That has a vibratory frequency as well, a resonance. We talked about that before. That resonance is very different than the resonance of the vocal chords that set up the initial vibration that carries most of the power in the speech, and that resonance is determined by the size and the shape of the tract cavity. And that's, if you want to think about it in terms of a musical instrument, that's similar to the size and the shape of the body of, let's say, a wind instrument like a clarinet or an oboe or what have you, that again has a resonance that's modulating the frequency that's set up by the vibration of the read or the blow hole. So these resonances of the vocal tract add to the resonance characteristics, the vibratory characteristics, of the vocal chords, and the combination of those two establish the recorded spectrum that actually comes out of the mouth. We'll say more about the spectrum. I just wanna remind you that these spectra are snapshots of the time signal of the sound that is being generated by the chords, the resonance properties of the tract, or recorded as what actually is uttered by the speaker. The combination of the vibratory frequency of the chords modulated by the resonance of the vocal tract sets up a series of peaks, and these peaks, and this is going to be important for what we're talking about later today and subsequently, these peaks are called formants. So that's the first formant here, the second formant here, the third formant here. Formants are the name given to these peaks that are vital in the determination of the sound that we hear, so the peaks of the formants determine what vowel sound. So when you say i, e, o, u, or what have you, those peaks are changing and distinguishing one vowel sound from another. So I just wanna demonstrate this or suggest that you demonstrate it to yourself so that you're aware of the power, that's in the vocal sound that's generated by the letters. If you put your finger on your Adam's apple and say a vowel sound, e, you can actually feel the vibration of the vocal chords coming through the tissues of your neck as you place your finger on the Adam's apple as a signature of a vibratory power that's generated by the vocal chords. Of course, not all speech sounds are vibratory. There are speech sounds, about half of them we'll talk about those in a minute, that are not voiced, that don't depend on vibrations of the vocal chords. Those are consonants or unvoiced speech sounds, and they depend on the shape on the vocal tract but they don't depend on the vibration of vocal chords. That also applies when you whisper. When you whisper, if you put your finger here and enunciate a vowel and then whisper the vowel, you'll feel that the vibration goes away. So this is Lee's model of vocal sound generation, and it was established in the 19th century by Johannes Muller, a German physicist and auditory physiologist in those ancient days. And that's stood the test of time, and it's basically the way people today think about the generation of speech sounds. So, what does all this have to do with music? Well, I think it should be obvious from what I've been telling you, that the vocal tract, as I've just described it, has all of the characteristics of a musical instrument. The vocal cords are equivalent to the string, let's say, or the violin pictured here. They're setting up the vibration when they are activated by a force. The force is the air being expelled for the glottis, the opening between the vocal chords, and it accelerates according to Bernoulli's principle just in the same way that the water in a river would accelerate going through a narrow gorge. This is a narrowing in the tract below the larynx. And the acceleration of air, that pressure, pushes the vocal folds, the vocal chords, apart. And when the pressure is reduced they come together again, and that sets up the vibration that you can feel with your finger. So the force is equivalent to bowing of the string, and the modulation imposed by the rest of the vocal tract is equivalent to the modulation that's imposed by the body of the violin. The string by itself, that's not what's producing the sound that we love to hear. It's the modulation of that by all the characteristics of the body of the violin in the same way that all of the characteristics the local tract modulate the vibration and that powerful source that's coming from the vocal chords.
