The Science of Everything Podcast - Episode 53: Sound and Music

Episode Date: December 10, 2013

We begin with a discussion of the essential nature of sound as pressure waves in air, discussing matters such as the speed of sound, harmonic frequencies, loudness, standing waves, and the Doppler effect. We then apply these basic principles to understand the nature of music, and why different musical instruments sound different. Also discussed are the various aspects of music, including beat, pitch, melody, timbre, etc, and the differences between woodwind, percussion, brass, and string instruments. Recommended prelistening is Episode 24: Vibrations and Waves

You're listening to The Science of Everything podcast, episode 53, Sound and Music, and I'm your host, James Vodore. In this episode, we're going to look at sound and music, particularly the physics of sound, looking at speed of sound, fundamental frequencies, standing waves, we'll talk about harmonics, and then apply this to some interesting sound phenomena, for example, sonic booms and the Doppler effect.

And then we'll apply this basic knowledge also to gain a better understanding of music, including what music is, aspects of music. We'll talk about beats and rhythm and timbre and things like that. Also, we'll look at some of the major classes of musical instruments and talk a little bit about how those work and how they differ from one another. Recommended pre-listening for this episode is episode 24 vibrations and waves, which will provide some of the background necessary to understand, particularly the basic physics of sound. So, without further ado, let's get

started. Let's start by talking about the nature of sound. What is sound? Basically, the crucial thing to understand about sound is that sound is, well, it's a perception, so it's ultimately a construction of the brain, but in terms of the physical basis of sound, it is merely variations in air pressure caused by vibrations of air molecules. That's fundamentally what sound is, vibrations of air molecules and resulting changes in air pressure. And so everything that we hear, music, and voices, other sounds, everything, is just different patterns of variations in air pressure and different combinations of those patterns of variation

at different speeds and times and frequencies and so on. But fundamentally, that's all it is, variations in air pressure in differing patterns. So, thanks for listening. I hope you enjoyed this episode. Oh, wait, you want some more information? Okay, well, maybe we'll give a few more details than just that. So it is true that sound is essentially just variations in air pressure,

but there is a lot more to say about it than just that. Specifically, what do we mean by variations in air pressure? Well, when an object vibrates, what happens is that it's moving backwards and forwards very rapidly. Think about a tuning fork, which is just a basically a Y-shaped piece of metal that you can pull back and cause it to vibrate on the spot, and it produces a single tone of a given frequency. As the piece of metal in the tuning fork pushes outwards, it pushes air away, creating a compression, a wave crest.

As it vibrates backwards in the other direction, it creates a partial void of air, which is called a rare refraction, corresponding to a wave trough. And so, compressions are segments or sections of relatively high air pressure, rare refractions are areas of relatively low air pressure. And so as the tuning for pushes outwards and inwards again, you get this alternating sequence of compressions and rarefractions, or in other words, alternating sequence of high and low air pressures. And as the air molecules are rushing backwards and forwards, to move away from the areas of high pressure into the areas of low pressure, we have a regular pattern of sound, which we can perceive with our ears. So that's the basic nature of sound, compressions and rarifactions caused by vibrating objects. Those objects can include, say, a tuning fork, or they can include strings in instruments, or they can include our vocal cords. Many of the things that vibrate and produce sounds are actually strings of various forms, and we'll talk a bit more about that later when we get into musical instruments. For example, our voices are fundamentally just strings which can vibrate at different frequencies there by producing sound that we can hear.

Now, the speed of sound, how fast does sound travel? Well, most people, I think, know that the speed of sound is a lot slower than the speed of light. The speed of sound is about 340 metres per second in air at room temperature. Interestingly, the speed of sound does not depend on air pressure. So the speed of sound is the same at sea level as it is at higher altitudes. Well, it actually isn't because the speed of sound does depend on air temperatures, and of course, it's colder at higher altitudes, and so the speed of sound does decrease as you move higher above the surface of the earth. But it's not because of the lower pressure, it's purely because of the lower temperature. So the reason the speed of sound does not depend on air pressure is because if you have a higher pressure gas, so a higher density of particles, each particle has a smaller distance to vibrate or to travel through before it will collide with a neighboring particle.

However, there are also more particles that the energy must pass through because you've got high pressure. So these two factors, it will exactly cancel each other out. So basically, the total rate of progression of the air vibrations is exactly the same, regardless of what the density or the pressure of the air is. It does depend on air... The speed of sound does depend on air temperature, though, because with higher temperatures, the air molecules are moving more rapidly. They're vibrating around more quickly.

We've talked about that in previous episodes on gases. and therefore the air vibrations or the differences in air pressure can be transmitted more rapidly. Sound travels more quickly at higher air temperatures. It also travels more quickly in gases with lighter molecules. Now this is why if you inhale helium, your voice becomes high-pitched. That's occurring because the speed of sound is increasing in helium relative to air because helium is lighter than air. Therefore the molecules of helium can vibrate more rapidly or move more rapidly.

with a given amount of energy, because they're smaller, and so they don't require as much energy to move. Conversely, if you inhale gases like, I think it's sodium hex of fluoride or something like that, which is the one that makes your voice go really deep, it's because of the exact, it's having the exact opposite effect.

The speed of sound is reduced relative to the speed of sound in normal air because those molecules are much heavier and therefore take more energy to move them, and therefore a given amount of energy input into the system won't be able to move the molecules as much, and so therefore you have a slower rate of propagation of the vibrations, and therefore sound travel slower and also at a lower frequency, which is why your voice sounds lower. So there's actually two effects there, the change in the frequency and the change in the speed of air, but they both are product of the size and weight or mass of the molecules, be it the helium or the air.

Another important concept to understand about sound is that of fundamental frequency. To understand fundamental frequency, you have to understand the concept of a standing wave. Now, I talked about standing waves back in episode 24, and if you're not really familiar with what those are, I'd recommend going back and listening to that. I'll briefly review it here, but if it's a concept that you haven't encountered before, it can be a little bit tricky to get your head around. The basic idea of a standing wave is that it's a wave, so it's some sort of moving variation of something, some medium, but it's a wave that's stationary in position.

So a classic example of a standing wave is like a skipping rope moving up and down. The bits of the rope are moving, but the rope itself doesn't move from one place to another. So the rope stays still, parts of it move around. And so you have variation in, you can have energy transmission, or really energy storage, in standing waves without actual movement of the energy over space. Again, if that's unclear, go back to episode 24 where I talk more about what's standing waves are and how they work. But think of a skipping rope going up and down without actually moving over space. That's the basic idea of a standing wave.

Now, much sound that we produce particularly in musical instruments and also vocal sounds are the result of standing wave patterns. So a standing wave will occur for, will be produced, for example, if you pluck a string which is fixed at at least one end and then allow the wave to reflect back and interfere with itself, you'll get a standing wave pattern. Now the fundamental frequency corresponds to the longest possible wavelength that a given string can support. And this will be equal to twice the length of the string. It's twice the length of the string because you can have a node at both ends, and therefore you'll have half a period stretching across from one end of the string to the other, from one node to the next.

That's half a period. Remember, a period has to go up and then come back down, and then go down and come back up again. That's a full period. So the fundamental frequency corresponds to... The fundamental frequency corresponds to a wavelength that is twice the length of the string. So if you have a pipe or a string or something like that, because you can have a standing wave in a pipe as well. It doesn't have to be a string. You can change that by either changing the length of the pipe or changing the length of the string,

or by changing the speed at which waves travel through the pipe or the string. This latter possibility, changing the speed of wave travel, can be achieved by changing the gas. Again, as we've just discussed before, you can replace air, which is mostly oxygen and nitrogen, with a lighter gas such as helium. And in lighter gases, as we said, waves travel faster and therefore you have a higher fundamental frequency. Heavier gases, waves travel slower, and therefore you have a lower fundamental frequency.

So now that we understand what the fundamental frequency is, we can talk about harmonics. Harmonics is probably a word you've heard before, or another equivalent, well, mostly equivalent concept is that of resonant frequencies. These terms are sort of thrown around a bit in the media or in television and things like that, but often not used very carefully.

To understand what resonant frequencies are or what harmonics are, we need to know what the fundamental frequencies. So the fundamental frequency, again, as we've said, is the frequency of vibration that corresponds to the longest possible wavelength that a given vibrating string or pipe or something like that can support. And again, this longest wavelength will be equal to twice the length of the pipe or the string, if it's confined at both ends. So if you have a string pinned down at both ends,

the fundamental frequency will correspond to a wavelength, twice the length of that string. Now, what about the harmonics? Well, harmonics are simply frequencies, resonant frequencies, that lead to stable, self-reinforcing, standing wave patterns that have smaller frequencies than the fundamental frequency. So, let's break that down a bit. Let's imagine that I have a string that's fixed at both ends, and I pull the string down and cause it to vibrate, and I get a nice standing wave pattern.

There's a wave traveling back and forth across the string, therefore, leading the string to move up and down in a certain pattern. And the frequency of this wave, this standing wave, will be, I'm assuming that this is the fundamental frequency, so the frequency corresponds to a wavelength of twice the length of this string. Now, what if I want to have other frequencies in this wave as well? There's various reasons you'd want to do that, which I'll talk about it in a little bit, but suppose I want to have different frequencies. How could I do that? Well, one question is, could I have any lower frequencies? That is, frequencies corresponding to longer wavelengths.

The answer is no, because remember the fundamental frequency is defined to be precisely that, to be the lowest frequency possible. If you wanted to have a lower frequency, you'd have to increase the length of the string or length of the pipe or whatever, or of course change the speed of the medium through which the vibrations are occurring. But let's assume we can't do either of those things. So we can't have any longer frequencies because basically the string is too short to allow that. However, there's another question.

can we have any shorter wavelengths or can we have any lower frequencies? The answer is yes, but we can't just have any old frequency that we like. So, for example, suppose that we have a fundamental frequency corresponding to a wavelength of, I don't know, 10 metres, we can have higher frequencies than that corresponding to shorter wavelengths,

but we can't just have any old wavelength that we like. We can't have a wavelength of, say, 8.5 because that will not correspond to a nice, stable, self-reinforcing standing wave. Standing waves are only possible at certain lengths. So, for example, if you had a fundamental frequency corresponding to a wavelength of 10 metres, that means your string is 5 metres long, remember, half the fundamental wavelength. You could have a wavelength producing a standing wave of half of that, of 2.5 metres,

or half of that again, 1.25 meters. You can keep harming. That's fine, because those will produce consistent self-reinforcing standing wave patterns. So, for example, instead of having nodes at each end of the string and an antinode in the middle, antonode, remember being the place where the string moves from its maximum to its minimum extensions, and nodes being points where the string doesn't move. So you've got, in our imagine an example, with a string fixed at both ends, you've got node at one end, antinode in the middle, and a node at the other end. You can also have a standing wave, so that's the fundamental frequency,

the longest possible wavelength that we can have. We can also have a different pattern where we have a node at one end and a node at the other end, and also a node in the middle, and two antinodes, one in between the first node in the middle node and the final node. So in this case, we have three nodes and two anti-node instead of just two nodes and one antinode in the fundamental frequency case. And you can keep expanding that. You can have, instead of just, you can go two nodes, which is our fundamental, or you could have three nodes, which was our second case, or you could have four nodes, five nodes. You can keep going and increasing the number of nodes you have.

each time you'll be reducing the wavelength of your standing wave and therefore increasing the number of sort of up and down cycles that you have along your standing wave pattern and also you'll therefore be increasing the frequency of your standing wave but you can only do this in whole number multiples of your fundamental frequency so you can have a frequency that's double your fundamental frequency or three times your fundamental frequency but you can't have it at 2.6 times or 7.8 times those will not produce those length relationships or those frequency relationships will not produce consistent self-reinforcing standing wave patterns. It's quite difficult to explain this, as I often say, without the aid of diagrams.

So if you're finding this difficult to understand, try just Googling standing wave or harmonic frequencies or something like that. I'll also post some of these up on the Facebook page to make it a bit clearer. But again, strongly recommend that you listen to episode 24 where I talk about standing waves in a bit more detail, so you can get an idea of how that all that works. But the basic idea, again, is simply that harmonics are the resonant frequencies or the frequencies that you can have producing standing waves, so self-consistent waves that can maintain themselves, for a string or other confined vibrating structure, of a given length. So, again, if I had a 10 meter, sorry, if I had a 5-meter long string, my fundamental wavelength is 10 meters, again, twice the length of string, I could then have fundamental frequency, I could then have resonant frequencies corresponding to my fundamental wavelength. wavelength of 10 meters, of half that, five meters, half that again, 2.5 meters, half that again, 1.25 meters, and so on and so on. I can keep having smaller and smaller resonant frequencies. These are my harmonics. Each one of these is a harmonic. So there's your first harmonic and your

second resonant harmonic and your third harmonic and so on. There's no limit to the number you can have, but there are only discrete numbers that you can have. There's no one and a half resonant frequency or one and a half harmonic. Doesn't make sense. It won't produce a consistent standing wave. If you try to have a standing wave pattern like that, what it would happen is that the wave would not interfere with itself in a consistent way, would interfere with itself in an inconsistent way, is it reflected back from one side of your confined space to another, and it would interfere with itself, canceling itself out, and basically you would just get, you would just get nonsense, you would just get chaos and it would cancel out to zero. This is like when you're skipping

with a skipping rope, you have to put the energy in at the right periods of time. You can't just sort of waggle it randomly, wiggle it randomly, you won't get a nice standing wave, you won't get a nice skipping pattern with a skipping rope if you just wiggle it around randomly. Same with a swing. You can't just push at random times on a swing. You have to push it at just the right times. You don't have to push the swing every time that it swings back in your direction. You can push it every second time or every third time or every 10th time. But if you start trying to push it every 1.7th time, so you're pushing it when the swings hasn't actually come all the way back to you. You're pushing it sometime in the middle, you'll just get chaos. The swing will bounce around and it will go all over the place.

You won't get a nice swinging pattern. So in order to have nice, self-consistent waves, you need to have whole number multiples of your fundamental frequency. And these whole number multiples are called resonant frequencies or harmonics. The harmonics differ depending on whether you have a string or a pipe or anything that's confined at one end only, and then open at the other one, or confined at both ends. So these different types of standing waves have slightly different, well, they have different harmonics, they have different

patterns, even on odd, but we won't get into the details of that. Suffice it to say, they both have harmonics, and they both have to be whole number multiples of your fundamental frequency. So, hopefully that was relatively clear, it's a little bit complicated. This is important, though, because we'll come back to talking about harmonics when we get to talking about music and

the different types of musical instruments and how we play different notes. Before we get to that, though, there's a few more basic concepts of sound, need to cover. Now, I've been talking about harmonics and different frequencies. I suppose I should make one thing clear now, which I've sort of hinted at, but the frequency of vibrations of those air molecules or, you know, of the harmonics that you have, that corresponds directly to the pitch of sound that we hear. So high pitch corresponds to a high frequency, and therefore a small wavelength. Low pitch corresponds to a low frequency and a long wavelength. So if I talk in

a low voice like this, what I'm doing is I'm vibrating my vocal chords with a very, sorry, a very low fundamental frequency and therefore a long wavelength. And we perceive that, we perceive that type of vibration as having a low pitch. Similarly, if I talk in a high voice like this, which I can't do very well, what I'm doing is vibrating my vocal cords with a much smaller wavelength and therefore a lower frequency and therefore that's perceived as a higher pitch. and again we'll get back to that when we talk more about music. But there are some other properties of sound that are relevant, apart from just frequency and harmonics,

which we've been mostly talking about so far. And another one is loudness. So this one's a bit more intuitive. Loudness basically just refers to how intense the sound is, and it corresponds to how far away from their equilibrium position air molecules are being vibrated as the energy passes through them. So, for example, if I tap my desk softly, I don't know if I can hear that, but if I make a soft tapping, that produces a sound, you can hear that, but because I'm not imparting very much energy into that, into those air molecules as they're vibrating, the air molecules don't vibrate very far away from their equilibrium positions. They only vibrate a little bit, basically, and therefore they don't displace very much air. There's not much of a change in air pressure, and we perceive that as a fairly soft sound. On the other hand, if I make a very, loudbagging, if I put lots of energy into producing the vibration, then what I'm doing is I'm

causing the air molecules to vibrate more away from their equilibrium position. They're vibrating more, you're having larger variations in air pressure. We perceive that as a loudest sound. Now, it's important to understand that this is, loudness has nothing to do with the frequency of the sound. You can have loud, high frequency, loud, low frequency, and so on. Loud, high frequency, loud, soft high frequency. They're completely different from each other. The frequency has to do with the frequency of vibration of the air molecules. There's really no other way of saying that. Loudness has to do with basically the amplitude of vibration of the air molecules. And if you remember from vibrations and waves, amplitude and frequency are completely different from each other. Amplitude is how far away you move,

frequency is how often you repeat a given motion. So they're completely different things. As you're probably familiar with, the loudness or volume of sound is typically measured in decibels. Now, decibels are actually a logarithmic system, so that means if you increase from 80 decibels to 90 decibels, that actually corresponds to a tenfold increase in intensity of the sound. But decibels are a bit confusing, not only because they're a logarithmic system in this way, but because also the decibels measure, what they measure directly is the actual energy in the sound, so the actual vibrational energy. Now, higher vibrational energies correspond to louder sounds, but the relationship is a very complicated one. So it's not necessarily the case, in fact it definitely is not the case, that a sound that has 10 times as much energy, so therefore is 10 decibels higher, sounds 10 times louder to you. The relationship is very complicated, and psychoacousticians have spent a lot of time studying this about equal perceived loudness curves, and it actually depends on the frequency and lots of other things. So when I said there's no relationship between loudness and frequency, that's true from a physics standpoint, but it's not quite true from a psychological standpoint, because the way we perceive sound does depend on the frequency. So, you know, 50 decibel sound at 100 hertz won't necessarily sound as loud as a 50 decibel sound at 2,000 hertz, because we perceive different frequencies of sound differentially well, and different people, of course, will differ in this as well. By the way, frequency is measured in hertz. I think I would have discussed that.

in episode 24, which is just the number of vibrations per second, so 1 hertz is one vibration per second. Human ears are sensitive to sounds between roughly 20 and 20,000 hertz, so that's between 20 hertz and 20 kilohertz. Sounds that are above this threshold, that is, with high frequency, are referred to as ultrasonic, sounds that have a lower frequency than 20 hertz are referred to as infrasound. You might have heard those terms before ultrasound and infrasound, because they're used, for example, ultrasound is used in medical applications for imaging. So, in some sense, it's a little bit strange when we think about ultrasound producing a visual image, because what we're actually doing is transforming vibrations of air molecules into a visual image,

which we can then see. Normally, the way our normal sensory apparatus works is that we transform vibrations of air molecules into sounds which we hear, but there's no reason you can't transform it into a visual image as well. In fact, this is what I'm doing right now, as I'm recording this podcast on Audacity. I have a visual representation of the volume, at least. at least that there's no representation of pitch, but there is a representation of the volume of sounds that I'm producing in terms of the height of this little graph thing that's going up and down.

That's just a different way of basically perceiving the physics which is going on. The physics is just changes in air pressure of varying intensities. Our ears and brains perceive that as sound, but we could use, say, an ultrasound and perceive that as an image or as all sorts of other forms. And as everyone knows, different animals have different sensitivity ranges for different frequencies. So bats, for example, can hear much higher frequencies than we can, and they use that for echolocation.

Everyone also probably knows that dogs can hear whistles that humans can't. That's because the whistles produce such high frequencies that humans can't hear them, but dogs can. So this is all just simply about the sensitivity to different frequencies of sound. And again, that's coming back to fundamentally what frequencies the organs in our ear can resonate with. Okay, there's just a couple more effects that I want to talk about before we move on to talking about music These are sonic booms and the Doppler effect

Which are two things you may have heard of before Sonic booms occur when objects travel in Travel faster than the speed of sound Or specifically when objects travel When objects in a given medium travel faster than the speed of sound in that medium So you can have sonic booms in water as well We don't usually call them that but that's what they are A sonic boom is just a shockwave

It's produced, as I said, when an object travels in air faster than the movement of sound in air itself. Now, again, it's very hard to describe how this works without a diagram. I'll make an attempt, though, and we'll see how successful it is. As an object travels faster, the crests of each wave pulse of sound that that object produced, say an airplane, it's producing sounds as it moves from its engine, the crests of each of those wave pulses become bunched closer and closer together. Now, to see that, imagine that my aircraft, let's, let's, let's, instead think about it as ripples in a pond, because this is the same basic principle.

Ripples in a pond are analogous to sound wave, pressure waves in air. If I just drop a bunch of stones into a pond at regular intervals, I'll have a series of ripples coming out from the spot where I'm dropping the stones, but there won't be any, there's no movement, I'm dropping them in the same spot. Now suppose that I start moving the place, moving my hand across the surface of the pond and so that I'm dropping stones in at slightly different spots. what you'll see is that the wave crests will move across the surface of the bottom, of course, because I'm moving the place where I'm dropping the stone in.

The faster I move my hand, the more rapidly these wave pulses move relative to one another. And now it turns out that as the speed of the object in the medium in which it's traveling increases, those wave crests begin to bunch up in the direction in which the object is traveling. So again, go back to our case of the aircraft traveling through air. the wave crests of the sound produced by its engines begin to bunch up near the nose, or near the forward section, of the aircraft. And this is because basically what's happening is

the aircraft emits one pulse of sound, at one period of time, imagine, and then at the next period of time, it emits another pulse of sound. But in the intervening period, the aircraft has travelled forward. And so wavefront traveling in the forwards direction from the initial wave produced by,

wave of sound produced by the aircraft, catches up to some extent to the wavefront produced in the second period. The reason is because, of course, the aircraft is moving during that period of time. So the fact that the aircraft is moving is what helps the second wave crest catch up to the first one. The faster the aircraft is moving, the more catch up the second wavefront gets relative to the first one. And if the wave... sorry, if the aircraft is moving sufficiently rapidly, all of those wavefronts will bunch up right in front of the aircraft. If that wasn't very clear, and I don't think it was, because it's so hard to describe this without drawing a diagram.

Again, just look up Sonic Boom on Google Images, and you'll hopefully see what I'm saying. It's probably even better to look at an animation, because it becomes immediately clear why the waveforms bunch up if the object is traveling sufficiently fast. So it's very clear from an animation. Look one up if it's hard to see what I'm saying. But the basic point is that the object is trying to push air in front of it away at a rate faster than the air can, get out of the way because the object is traveling faster than the speed of sound. So the air can't get away in time. So what happens? You get a very substantial buildup in pressure in the form of a very high amplitude wave in front of the object. And as the object, say our aircraft, is travelling towards us,

this high pressure, really high amplitude wavefront will at some point pass us by. So we will hear this very high amplitude, very high pressure buildup of air as a very large sound, specifically as a sonic boom. There's actually another sonic boom which occurs at the tail of the aircraft, for the exact opposite reason. At the front of the aircraft, the sonic boom occurs owing to the fact that it's pushing air out of the way faster than air can actually get out of the way. At the tail of the aircraft, the air is being moved away faster than the air can return to fill the space produced by the aircraft. And so you have a similar effect of a very low pressure, very low, amplification. A very low amplification. wave occurring at the tail of the aircraft.

A sonic boom is actually not a static phenomenon, a phenomenon, because this wall of very high pressure and very low pressure at the tail of the aircraft travels along with the aircraft, so it's always there, so long as the aircraft is traveling faster than the speed of sound. It constantly travels along with the aircraft in an envelope, which we can call the sonic cone. However, we don't hear it as a continual noise, we just hear it as a boom, one-off thing. And the reason for that is because you will only be standing at the position of the aircraft's sonic cone at one point. In other words, the aircraft is traveling towards you. For a long time, you're in front of the sonic cone, then at some point you're standing right in the sonic cone.

That's when you hear the sonic boom, and then afterwards, you're behind the sonic cone as the aircraft flies on further in front of you. So you will only hear the sonic boom once as it intersects your position. If you were somehow able to travel along inside the sonic cone, then you would be able to hear it continually, which just sound really, really loud, continually, although I guess there'd be problems there because the rate of the sound traveling towards you would be slower than the rate at which you were actually traveling. So there might be complexities there, but basically, if you were able to travel along with the aircraft, you would hear a continual noise rather than just a one-off boom. But it all, it all has to do with the fact that the aircraft or other object is trying to push

the air away from itself, faster than the air can get away. And so the wavefront's all bunched up and produce a very high amplitude, high pressure, and therefore loud sound that we can hear. And the exact same phenomenon is produced by boats that travel through water. You know those wakes, those sort of white wakes that they leave behind them. That's basically the same thing as a sonic boom. It's just in water rather than air. The boat is traveling faster than the wave speed of water waves in the water, and therefore you have this very high amplitude build-up of large waves, wave crests that's left behind in the wake of the craft.

So those wakes in water are exactly the same phenomenon as sonic booms in air. Final phenomenon that I want to talk about before moving on to music is the Doppler effect. The Doppler effect is sort of similar to a sonic boom in the reason it's produced. It's again produced by when objects are moving towards us or away from us, and is caused by the fact that the apparent frequency of a sound changes.

So the Doppler effect occurs when you have an object, which is producing a sound, and is also moving radially relative to you. So that is regularly, meaning it's moving towards you or away from you. If an object is just moving sideways relative to you, that you won't have a Doppler effect. The Doppler effect itself is simply the fact that if an object is traveling towards, you, the frequency of sound that it's producing is increased. So you hear a higher frequency than, say, an observer who is travelling alongside the object would. Conversely, if the object's travelling away from you, then you hear a lower frequency than would an observer who's travelling

along with the object. So a classic example here is the sound of an ambulance or a police car or something like that. As it's coming towards you, it appears to have a higher pitch, and as it travels away from you, it appears to have a lower pitch. That's because of the Doppler effect. Again, the physics behind that has to do with the fact that the wavelengths, the wavefronts are bunching up when the object is moving towards you, and they're spreading out when the object moves away from you. Bunching up corresponds to a reproduction in frequency, and so you hear a higher pitched sound. Spreading out of wavefronts corresponds to a lower frequency, and therefore you hear a lower pitch. If that's unclear, see a diagram or an animation to see how that works.

radar and also sonar in water works by this principle. You reflect radio waves often a moving object. Measure the time to return. That tells you how far away the object is. And also measure how the frequency of the waves has changed. And that will tell you how fast the object is traveling. Or at least it will tell you the radial velocity of the object. It won't tell you its velocity is sort of sideways relative to you.

So radar can tell you both the distance away from you and object is and how fast it is traveling. And if you combine, if you had radar at several different points and you used them on the same object, you could combine this information to actually work out a three-dimensional pattern of motion of the object. So that's how radar works. Okay, so now that we've covered some of the basics about sound and frequency and harmonics and so on, it's time to talk a bit about music. Now, caveat here is, I am not a musician myself, and so everything that I'm going to present here is purely sort of theoretical,

particularly when we talk about some of the different aspects of music, there are not always clear and concise definitions of these things, and so some musicians might use the words a little bit differently to how I'm going to use them, but I'm presenting them as far as I could discern their meaning through my research, so that's how it's going to be, basically. So that's my little caveat. First of all, what is music? So you could probably spend an entire podcast episode trying to define music,

so I'm not going to do that. I'm simply going to define music as a series of periodic sounds and silences. that's very important, sounds and silences, that is pleasing to the ear, or that is nice to hear. Musicologist Jean-Jacques Nettieres, I've probably mispronounced that, says, I won't read the full quote, but basically there's no real distinction between music and noise, something that's perceived as merely noise in one culture may well and can easily be perceived as music in another one. There's no real difference between music and noise, basically. It's a cultural thing, and maybe part biological as well, in terms of what humans can hear

and tend to find pleasing cross-culturally. So there's no hard and fast definition of what music is. It's just patterns of sounds and silence that we like to listen to, basically, in a given culture. Now, what are the different aspects of music? Music is a very complex phenomenon, and it has many different properties. I'm going to talk about some of them here. If you're not terribly well acquainted with music, then you would have almost certainly heard all of these before, but maybe not really understood exactly what they mean.

If you are acquainted with music, you may agree with some of my definitions. You may think that some of them are slightly different to how you. use the terms, again, that's fine because pretty much all of these terms, pretty much none of these terms have precise, well-defined definitions. But nonetheless, I'll give it a go. So, specifically the aspects of music that I'm going to be talking about are tempo, melody, dynamics, pitch, harmony, rhythm, and style. There are some other ones too, but these are some of the main ones and some of the more fundamental ones. And variations in all of these different aspects of music is what give different pieces of music their own unique sounds, qualities, and properties,

etc. So, start with the tempo. The tempo is a relatively easy one. This is the speed or the pace of a piece of music. It's often measured in terms of beats per minute. Sorry, a metronome is a device used by musicians to keep a steady pace. So this is, you know, one of those pendulum things, well, sort of an inverse pendulum that ticks. I mean, you can get different forms of them. There's digital ones as Well, some musicians don't like using metronomes, but many will. And the reason is because it's difficult without a metronome to keep a steady, consistent pace. There's a tendency to speed up or slow down in various parts. There are many words that are used in music to describe tempo.

Many of them are Italian in origin. So, for example, accelerando means a piece that's slowly accelerating, slowly increasing in tempo. Allegro means a piece that's quick and lively, and there's other words for slow pieces and for fast pieces and for decelerating and all sorts of sudden changes in tempo and other things like that. But basically, tempo is just the pace or speed at which notes or beats are played. So the next one, dynamics. Dynamics generally refers to the volume of a note, and also how the volume and emphasis of notes changes over the course of a piece.

There's slightly different definitions, but it's basically to do with volume, loudness, and emphasis. Traditionally, music is marked with either a P for piano, meaning soft, again, these are Italian words, or f for forte, meaning loud. You can also have two Fs, which means even louder, or two-piece meaning even softer, and again, there are many other combinations and variations of that. There are other terms like crescendo, which means becoming louder over time,

or piano forte, which means soft, and then an immediately strong, much louder note. Yes, okay, so that's dynamics, and next is pitch. Pitch is the frequency of the sound, with high frequencies and low frequencies, again, perceived differently by the human ear. It's important to sound that pitch is different to frequency. Well, I've sort of just said that the same thing.

Frequency is really a physics term, referring to the number of oscillations you have per period of time. That's measured in hertz. And we can quantify musical pitch in terms of frequency. But pitch as a musical term is really a psychological phenomenon. Humans perceive different frequencies as having different pitch, but not in a completely consistent or in a simple way. So it's not necessarily the case that one frequency corresponds to one pitch. People will differ in terms of how they perceive these things, environments and circumstances and so on will differ as well.

So pitch refers to more the musical subjective aspect, whereas frequency is more the just purely physical phenomenon. Of course, without variations in frequency, you can't really have variations in pitch, but there's just not a clear, precise one-to-one mapping between the two. Pitch is often denoted in music by a combination of letters and numbers, so, you know, A4 and G-9 and things like that. Well, G-9 will be a very high note, but anyway, yeah, so these numbers and letter combinations, there's different traditions for this, but they refer basically to different pitches, to different frequencies of sound. You might have also heard of sharp and flat notes. A sharp note is played slightly higher pitch than its denoted letter and number combination would indicate,

and the flat is slightly lower. So it just means sort of tweaking it up or down a little bit in terms of frequency. So these first three components of music, tempo, speed, dynamics, volume, and pitch frequency, are relatively easy to understand because they all correspond to noticeably different components of music. Specifically, if we link it back to the physics, pitch corresponds to frequency, more or less.

Dynamics corresponds to intensity of the vibration, more or less, and tempo refers to the speed at which waves are travelling, more or less. It's not quite right, because tempo also sort of more refers to the speed at which notes are played. But you can kind of make analogies there with the basic physics. But now we get into more complicated,

aspects of music, which are a bit hard to link directly back to the physics and also harder to pin down as precisely. Now, so one is harmony. Harmony is the combination of and relationship between two or more chords that are played simultaneously. Now, when we say chord, what we mean is a sequence of notes or tones, basically. Now, harmony is often described, or at least sometimes described, as the vertical aspect of music.

If you think about traditional Western music notation where you have those... the horizontal lines and you put the notes at different locations on the, depending on their pitch. When we say the vertical aspect of music, we mean you can have two notes at the same horizontal position along your bar of music that are supposed to be played, you know, they're, sorry, two notes at the same horizontal position, but at different vertical positions, corresponding to different pitches. Now, the fact that they're at the same horizontal position indicates that they should be played at basically the same time, but the fact there are different vertical positions

indicates that they will have a different pitch. So you might have an A and a C or something like that. These would be referred to as different chords. So you might have different sequences of notes in one chord, say at a higher frequency or high pitch, and another chord being played simultaneously at a lower pitch. The harmony refers to the relationship between these two chords as they're played simultaneously. So you can have chords that are in harmony, so that have similar melodies, for example, which we'll get to, or that sort of complement each other, or you could have disharmonious combinations of chords,

which of course could be used deliberately to create a feeling of discordance in the music, for instance. So basically harmony, the vertical aspect of music, how chords of different pitches relate to each other as they're played over time. Melody is sometimes called the horizontal aspect of music, and it refers to a succession of notes, including their pitch and to some extent their rhythm, as they're played over time. So a melody is basically a succession of a small number of notes that is heard as a sort of a unit. So you might have do-do-do-do-do-do-do-do. That's a very simple melody of three notes, increasing in succession in their pitch. Often a given melody is used repeatedly throughout a piece of music, or you'll have different melodies combined in different ways.

So it's referred to as the horizontal aspect of music, because it describes how notes relate to each other over time. So how you have one note that's maybe a lower frequency, then you have a lower pitch, and then a middle pitch, and then a high pitch. note in a sequence like that. And you'll see how that's different to harmony where that talks about how different notes of different pitches are played at the same time, rather than overtime. Melody also incorporates elements of rhythm and of tempo as well, so the speed at which you play these notes, for example. So it's a little bit hard to define it precisely, which is why I made the caveat

earlier. The last, well, the second last aspect of music that I want to talk about is rhythm. this was the one I found the most difficult to define. I mean, it's something to do with the succession of notes over time. That's the best I could do in terms of a definition. You'll get different definitions elsewhere. I found it very difficult

to distinguish the difference between harmony, particularly between melody and tempo and rhythm, that they all seem to overlap a very large amount. Rhythm does seem to be a more general concept than melody, so melody is just a specific, generally refers to a specific sequence of notes. rhythm is more the overall pace and form of the piece of music.

So, for example, even the simplest piece of music, like a simple drumbeat, has a rhythm, but it doesn't necessarily have to have a melody. So if I have a drum beat that's just going, you know, that's a rhythm, a very simple rhythm. There's no melody there because I'm not changing the pitch over time, nor is there any harmony because I don't have, I've only got one chord in that instance. And, well, it has tempo, but there's something terribly much interesting to say about the tempo, because it's just constant. So rhythms are sort of a more basic concept,

but also more overarching. It has something to do with the melody and the tempo and the B, and they all sort of mix together. Hard to define. The last one aspect of music that I want to talk about is style. And this is the most general.

It really incorporates all aspects that we've talked about so far, so pitch, dynamics, harmony, tempo, etc. As well as Timbrae, which we'll get to in a moment. And the style is what distinguishes individual composers or groups, periods, genres of music, etc.

they all have different ways of combining melody and harmony and pitch and dynamics and so on in different combinations and in different ways producing a different style of music. A word that I've used a couple of times is Timbre. It's spelled T-I-M-B-R-E. I'm not sure if I'm pronouncing it exactly correctly. This is a bit of a tricky one because it sort of overlaps with a number of aspects of music that we've already discussed, but it's also a bit different. So specifically what Timbrey refers to is the quality of sound that different instruments will produce. It's also sometimes referred to as tone-color, because it sort of indicates it's a quality of the music. It's not its pitch, it's not its tempo, it's not even the rhythm. It's just the quality of the sound. So it will overlap to some extent with some of the other aspects we've talked about before, but it is a little bit different.

Specifically, the reason different instruments and maybe different bands and someone will have different timbrei is because they have different combinations of harmonic frequencies. So remember, if you play, so for example, let's consider playing, I don't know, a C, a middle C note on a piano versus on a guitar. If they're properly tuned and with a few other caveats, the fundamental frequency of both of those notes is the same. They're vibrating at the same frequency of however many hertz on both those instruments. However, the quality of the sound will be quite different. You'll be able to tell if it's being played by a piano or a guitar or by something else. The reason you can tell, I mean, you know, again, there might be differences in tempo and melody and so. on, but even ignoring those, if you just play a single note, so basically you don't have

any of these other confounding factors, you can still tell whether it's a piano or a guitar. The reason is because you have different combinations of harmonic frequencies that will occur when you pluck a guitar string versus when you press a piano key. And these different combinations of harmonics, so this is higher frequencies, produce different overall patterns of sound, which you perceive to be different. You know, we hear differently. So the fundamental frequency is the same, but the harmonics that are sitting on top of that are different. And what you hear is the combination of all of those frequencies added together.

So the overall pattern of sound, the quality of the sound will be different, even if the frequency is the same. So that's how different instruments, that's why different instruments, and also even just the exact design of the instrument, will produce slightly different qualities of sound, because they're producing different combinations of harmonic frequencies. Okay, so those are the main aspects of music. There's another thing that I want to talk about, which is that of beats. People talk about beats a lot, but I don't think many people actually understand what they are. So, I mean, it, In the most basic sense, a beat is just sort of a regular sequence of notes in a piece of music.

And so you generally measure the tempo by how rapidly the beat progresses. But there's also a more specific definition of beats, which is a periodic variation in sound volume caused by variations in the amplitude of different sound waves. So it turns out, if you have a sound that is a mix of different frequencies, and you add those together, what happens is that there will be periods where you get constructive interference of those frequency waves and therefore very loud sounds, and there will be other periods where you have destructive interference of those different frequencies, and therefore you get much quieter sounds.

And this variation in volume over time is referred to as the beat. So technically speaking, if you just have a tuning fork which produces a single frequency, you couldn't have a beat because it's only producing one frequency. To have a beat in this technical sense, you need to have more than one frequency. And of course, in any real instrument you will, because remember, according to the timbrey of the instrument, you'll get different patterns of harmonics adding up to produce different waves. Those differences in frequencies can give you beats. But in the specific sense, beats only are produced by differences in frequency. And particularly the beat frequency will be equal to the difference in the frequency of the two waves.

So if I have a 50 hertz and 100 hertz frequencies, my beat frequency will be 50 hertz there. That's the difference between the two frequencies. So if you have two sounds of a very similar frequency, the difference between those frequencies is small. So maybe I have a 79 hertz and an 80 hertz sounds. The difference in those is 1 hertz. One hertz is a very low frequency. And so that will be a very slow beat. Similarly, if I have very different frequencies, then I'll have a much higher, a larger difference in those frequencies, and therefore a much faster beat. Okay, so now in the final section of the podcast, I want to talk about some of the main types of musical instruments and just sort of compare how they work.

There are enormous numbers of ways of categorizing musical instruments. The one that I'm going to use is just a simple way that they generally are categorized in a classical Western musical orchestra. And this is generally, they generally split up into the string instruments, the woodwind instruments, percussion, brass instruments, and keyboard instruments. So we'll start with string instruments. As I, as you remember I said earlier in the episode, many musical instruments and sounds in general are produced by vibrating strings,

and so a classic example of this are string instruments. Examples of string instruments include harps, guitars, banjos, violins, cellos, double bass, etc. Now, the strings itself are pretty... The strings themselves are quite small, therefore they move very little air, and as a result you wouldn't be able to hear them very easily or at all, unaided. And so to overcome this, most string instruments are mounted onto a larger body, often made of wood or another material, and the musical vibrations produced by the strings are transmitted to this wooden or to this body,

and therefore the body itself begins to vibrate some air, thereby amplifying the sound of the string. And so the exact shape and design and even materials of the body of the instruments will influence how the vibrational patterns are produced. So this will affect the loudness, the harmonic frequencies that are produced and so on. So this is why even fairly similar instruments, like say compare a guitar to a banjo, or a violin, produced using a very similar basic idea, you know, you attach a vibrating string to a wooden instrument, to a wooden body, can still produce very different sounds because the vibrations are being transmitted in different ways and you have different harmonic frequencies

and such. String instruments are played by vibrating the strings, as I said before, and also the musician, in order to play different notes, notes of different pitches, will need to alter the length of the strings. Now they can't do that by manually changing the string length or changing the strings tension while they're playing. So instead what they do is they move their fingers around and manually alter the effective length of the string. So that's what a guitarist is doing when they're moving their fingers around. They're just changing the length of the strings of the guitar, thereby changing the frequency of the fundamental frequencies of the sounds that they play. And of course there's going to be more complexities to it than that, but that's the basic idea of what they're actually doing. When you tune, say, a guitar, what you're actually doing is, you know, turning those knobs on a guitar, that's actually varying the tension of the string. And that also will change its pitch. So remember, pitch is determined by the tension of the string, the mass of the string, and also the length of the string. A guitarist or other string player can't change the tension of the string while they're playing the instrument. So instead, while they're playing, that they move their fingers around. So they finger the strings. But to tune it in between performances, that's what we're playing. That's what we're playing.

why they use those knobs to alter the tension in the strings. An electric guitar, so far I've been describing an acoustic guitar, which again, you vibrate the strings, which vibrates the body of the guitar, and that vibrates the air around it, and we hear that as sound. Electric guitars are different. What they actually do is convert the string vibrations into an electric signal, which is then amplified and played through speakers. So this is why, if you look at an electric guitar, it doesn't have to have sort of the hole in the center and the hollow body that surrounds the strings, generally an acoustic guitar will. So electric guitars can be flatter and smaller because they don't need to have the vibrating body that an acoustic guitar has to. Because the guitar itself

doesn't actually make the sound. What you're hearing is not the strings themselves vibrating or even the guitar itself. What you're really hearing comes from the speakers as amplified electronically. So that's how an electric guitar differs from an acoustic guitar. Also one other point about string instruments. So they're all produced by strings that vibrate, but you can vibrate the strings in different ways. So one way you can vibrate a string is just to pluck it. This is what you do in a guitar or a banjo. You can also bow the string, which is what is done in a violin or viola, and those produce very different sounds. Another way of producing a sound via a string string is. And this is what we do on a keyboard, particularly, for example, a piano. So pianos actually are, in a sense, string instruments, although they're categorized under the keyboard instruments in the categorization that I'm giving, because they use a keyboard. But fundamentally, they produce their sound using strings, just like a guitar does. Strings are obviously longer, and also they're to be made of metal in a piano, so they generally have metal strings, and the way that you cause them to vibrate is you press down a key,

which basically moves various internal mechanisms, ultimately striking, literally hitting the metal strings, and causing them to vibrate. As the key is, for as long as the key is depressed, the vibration continues. As soon as the key is released, the strings vibration will come to a halt because basically there's a dampener which is placed on the string causing it to stop vibrating. Different keys are attached to strings of different lengths and masses and therefore will produce different notes. So this is similar to the concept of the guitar where you have strings of different masses and different tensions and so on. And also changing the length of the strings changes the pitch. Same thing with the piano.

Pianos also have pedals which serve different functions. For example, one of the pedals called the Sustain pedal will cause all of the strings to keep vibrating even after you remove your finger. So this can be used if you want to play lots of notes vibrating at the same time and you only have a certain number of fingers. You can depress this pedal,

and all notes that you press will continue to vibrate until you raise the pedal, as opposed to, as I said, normally when the notes will only sound when you have your finger depressed on the key. So that's broadly how I'm up. piano works and that's in the keyboard instrument section of our orchestra that we're imagining here. So we've done string instruments and keyboard instruments. Let's now look at woodwind instruments. Woodwind instruments are, well, wind instruments in general, which include, well, I would include

woodwind and brass instruments. Some others would categorize them differently. But the reason I put those together is because woodwind instruments and brass instruments both are essentially just vibrating containers of air. I mean, you can say that that's basically what any instrument is. obviously they have to vibrate the air, but the difference between string and keyboard instruments and woodwind and brass instruments is that woodwind and brass instruments don't have strings. I mean, I'm sure there's some exceptions that have weak combinations, but, you know, traditionally, woodwind and brass instruments don't have strings. They just have the vibrating columns of air.

So basically, they're just a bunch of pipes and other containers that air vibrates through. One difference between string and wind instruments is that in a string, generally the, in string instruments, generally the string is confined at both ends, and so you have a node at both ends. Whereas in wind instruments, generally there's one closed end and one open end. Not always, but often that's the case. And so remember I said earlier that these different combinations of nodes and antinodes will give you different harmonic frequencies, get different sets of harmonics. And so that's one reason why wind instruments and string instruments will sound differently

because they have different harmonic frequencies. There are, of course, many other reasons. The instruments are differently shaped and they're made of different materials, and so the timbrey and patterns of harmonics and other things will be different. Now, remember I said that it, say when you're playing a guitar, the way that you change pitch is by moving, either playing a different string or just changing the length of the string using your fingers. In a woodwind instrument, the way that you change pitch is by altering the length, the effective length of the tubes by, for example, opening or closing holes along the tube. And this is what you see, for example, a flute player or a clarinet player doing when they're moving their fingers around. They're just opening and closing those holes, which are changing the relative, the, the,

the length of the different tubes in the instrument, thereby producing different pitches. Examples of woodwind instruments include flutes, oboes, clarinets, bassoon, and the saxophone. Now, an interesting note on the saxophone, I certainly used to think of that as a brass instrument, and maybe you do as well. Saxophones do tend to, well, can be made of brass, definitely they generally made of metal, whereas the other wind instruments, woodwind instruments are generally made of wood, but woodwind instruments don't actually have to be made of wood. what actually defines the difference between a woodwind instrument and a brass instrument is not what the instrument is made of, it's on how it produces its sound. So woodwind instruments use reeds or thin strips of wood to vibrate inside their columns, whereas brass instruments are just purely containers for vibrating out, so they don't have those wooden strips.

So there's a slightly different mechanism of producing sound in the woodwind versus brass instruments. Saxophones produce sound via the traditional mechanism of the woodwind instruments. that's why they're classified as a woodwind instrument, or at least a wind instrument. Brass instruments include trumpets, trombones, French horn, and the tuba. Again, in brass instruments, it's similar in that you play different notes by changing the length of the tubing, although this can be done in a different way. So, for example, trombone, in the famous case where you have the sliding component, you're actually, when you slide that outwards an image, you're directly changing the length of the piping,

not by opening or closing a hole or something like that, but you're actually changing the length of the piping. So that's, again, going to change the fundamental frequency that you're playing, and therefore the frequency that is heard. So that's brass and woodwind instruments. That leaves us with the final category, percussion instruments. So everyone knows percussion instruments. These include things like drums and symbols. These are actually, although sort of they look simpler,

a drum doesn't look as complex an instrument as a piano or a flute or something like that, but actually, in terms of the physics of what's going on, they're much more complicated. because it turns out that the resonant frequencies on the surface of, say, a drum, do not have to be whole number multiples of the fundamental frequencies. So that completely contradicts what I said before when I was talking about harmonics. But the harmonics that I was talking about definitely applies to strings and to wind pipes. So that's basically all the types of instruments we've talked about, except percussion instruments. In percussion instruments, you can have nodes and antinodes occurring in a wide variety of places on the surface of the instrument,

producing a very complicated pattern. And so the precise sound that you get when playing, say, a drum will depend not only on how hard you strike it, but also precisely where you strike it. The basic definition or distinction of percussion instruments that differentiates them from, say, woodwind or keyboard instruments is how they produce sound. They produce percussion instruments all produce sound

as a result of some surface being struck by something. It could just be the naked hand, or it could be some sort of beat, or, you know, a drumstick or something like that. So obviously, for example, a drum is a percussion instrument, but so is a xylophone, for example, because you're striking wooden plates. And so in that sense, a piano is actually kind of a percussion instrument, or it has a sort of quasi-claim to being a percussion instrument,

because, as you remember, it works by striking strings using hammers. And so in that sense, it's percussion, but usually because it has strings, it's classified as in its own category. So piano is an actually tricky one to classify. Anyway, that's all of the different types of musical instruments that I wanted to discuss and their properties. And that's all we have for this episode. Hopefully you enjoyed it. If so, please jump on to iTunes and give the podcast a favorable review.

That really helps to improve the visibility of the podcast and to track new listeners. You can also go onto Facebook. Just search for The Science of Everything podcast and give our page a like. You'll also find their diagrams and images that I've posted. up, helping to explain some of the concepts of the episodes. If you have any suggestions or feedback or criticisms or anything like that, send me an email. My address is Fods12 at gmail.com. That's F-O-D-S-1-2 at gmail.com. Thanks again for listening and I'll talk to you next time.