A while back I posted a video entitled “What is Sound?”. Obviously the title speaks for the content of the video. A student, although finding the information very useful, did have a question though. She wanted to know if I could expound on the second ingredient of sound, layers, as described in the video.
Well first off, you should at least watch the video so we are both on the same page. But if you are short on time, I basically described the three ingredients of sound to be 1. waves of air, 2. layers of frequencies, and 3. volume.
The first ingredient of sound is literally waves of air hitting your ear drum with each wave landing a certain amount of times a second, which, by the way, is frequency. You take several layers of those waves and stack them together, that would the second ingredient, and the ingredient in question; layers. The last ingredient being volume, which generally is self explanatory. If you at this point are still not sure what I mean, watch the video.
But the second one, layers, seems to be the ambiguous section that needs clarifying.
But before we get started and to ensure that you are starting with the correct concept to build upon, think of the layers horizontally instead of vertically. Don’t think of them as a stack of pancakes or layers on a cake. Think of them as books on a shelf or, essentially, a stack of books laid on it’s side.
And time is represented as left to right. Imagine if you had a video of a man putting books on a shelf and he was doing it from left to right. You would see the books stack up on the shelf from left to right as time went on and every one of those books would represent a layer. Now that we have laid the basic conceptual foundation, let’s get to it.
Every sound is made up of many layers of more basic sounds that give it it’s unique structure. A good way to describe this audibly would be the difference between one person clapping and an audience of 1000 applauding. The sound of clapping and the sound of applause are completely different, although applause is made up of many individuals clapping.
Whereas one person clapping would represent one sound, the applause would represent the product of many layers of sound (clapping).
If you listen closely to a car horn you can hear different 2-3 (or more) notes being played at the same time. As a matter of fact, they are designed to play notes that are dissonant (lacking harmony. Unsuitable or unusual in combination; clashing). That way they are unpleasant to the ear and get your attention. The car horn is a sound made up of layers of smaller sounds, which in fact are made up of layers of even smaller sounds.
These smaller sounds are called “Sine Waves”. Sine is a mathematical term that gets into all kinds of significant stuff, so don’t go there. All you have to know is that it is a pure tone and graphically it looks like this:
It is also known as a Pure Tone because it isn’t mixed with any other frequencies. It is a single standalone frequency. Listen to this example of one. It is at 500Hz or 500 “waves” per second:
Now if you take a bunch of those, all at slight or great frequency, volume, and length differences, you get all the other sounds in the world called complex waves. If we tried to illustrate this using the above sine example it would look like this:
But technically they look like this with the layers stack left to right and compacted:
Now there are several different visual representations now on computers of different sound waves, but that one above is the closest that we can get visually to sound. If you spread it out it looks like this:
As you can see even each wave is different. What that actually is, is a visual representation of each individual wave from all the different sources as they happen. I know that is quite confusing, but let’s put it this way.
Take the clapping and audience example from above. If you took a picture of each person in the entire audience when they clapped once you would have thousands of pictures right? In fact, if each person clapped 60 times and the audience was 1000 strong, that would be 60,000 individual claps.
Now, if you took those 60,000 pictures and laid them out from left to right in a line as they occurred in time, you would have a visual representation of the applause. Each picture would represent a sine wave, or basic pure tone. Many of the pictures would overlap, but that is fine. That just gives that one sound instance in time its uniqueness. It could a bit louder than the other individual pictures because there is more than one clap happening simultaneously in that instance in time giving it volume.
So, once again, any given sound (except the sine wave) is a complex combination of ‘layers’ of sound. And every sound (again except for the sine or pure tone) is completely unique in the world as no two complex combinations are the same.
Sine or pure tone is another subject all together. Since pure tones are pure, they are elemental. You can’t break them down any further, sort of like the elements of the planet as illustrated on the periodical table of elements. Interesting theory huh? Periodic table of tones? Perhaps another post.