Hi everyone and welcome to Kristal Cross Music Production!
This is the first part of the first chapter of this audio engineering class, called "The Nature of Sound"
Let's start from the basics: the physical phenomena that we refer to as "sound"
that comes to our ears and that we interpret as "music"
It's important to everyone who approaches this job, to everyone who wants to understand this world itself
To know about the nature of sound, straight from its foundation
Ready? Let us begin
We all have a daily experience with sound, and we all learned in school (more or less), that the sound is a vibration that moves through a fluid that reaches our eardrums
Sound always generates from a vibrating source, like the vocal chords, musical instruments, a speaker's diaphragm
Let's think for instance of a speaker's diaphragm:
A speaker's diaphragm behaves like this: it moves back and forth, vibrates back and forth and applies pressure to the air molecules
So it causes the air to compress and decompress
This compression and decompression alternation, generates what we call "wave motion"
This motion is constantly around us, the world's full of it. Think about the sea waves, for example.
Every kind of electromagnetic wave, like the sunlight, x-rays, radiations, etc...
The spring is a good example to try to understand how a wave motion works
A pressure applied to a spring's end, will move to the other end
And viceversa, obviously
In this case, we call it "longitudinal wave"
A sound wave is a longitudinal wave
On the contrary, a sea wave's motion is not caused by a molecule moving back and forth, but moving up and down
Like this
Imagine, for instance, a buoy
Actually the buoy moves up and down
Why does it move like this? Because of the vertical motion of the molecules
Sea waves seem to move horizontally, because of this motion
But, in reality, the molecules move up and down and so the buoy does too
Sound tends to expand in a straight line, and to open like a fan, especially when the frequency is low
It depends from the source that generates it, but we'll cover this topic later
Now, we talked about the wave motion: how do you picture it? How do you interpret it?
The measure is called "frequency", and it measures the number of times a wave goes through its cycle of compression and decompression in a second
Look at this wave right next to me and you'll understand that compression and decompression alternate rhythmically, but what's this rhythm?
It's the frequency, of course
It's measured in "Hertz", and the scale covers a full second
1000Hz are 1KHz
1000000Hz are 1MHz
Why am I saying this? Because sound, technically speaking, exists in every frequency possible
But the human ear cannot perceive them all, it perceive just a certain range of frequencies
This range is not the same for every human being, and doesn't have the same limits. For someone is wider, for other is tighter
Averagely we can say that the human range goes from 20Hz to 20KHz
Other living beings have also different ranges. Dogs, for example, can perceive sounds far above 20KHz
Now that we talked about the frequency, there's another important matter that we have to cover: the "wavelength"
The wavelength is the distance between two waves that you can see
And it depends on the sound's frequency
Different frequencies have different wavelengths
I know the scheme's scale doesn't reflect its real size, we're talking about a physical value
I know it can seem odd, but sound does follow that specific pattern, moving through air
Every frequency matches its wavelength, and you can mathematically measure it, to know how it behaves
You can calculate the wavelength with this formula:
And it applies to all wave motions, not only to sound
Now, regarding "speed": it's not that hard to understand it how far a wave can travel in a second in a specific environment
But the only environment we're interested in is air, we can consider it a fixed value
And this value equals to 340m/s
Quick hint: write down the formula and everything I said this last minute
Because it could save your ass when you're dealing with it in during a live gig
We can safely say that the larger the wavelength is, the lower the frequency will be. Or vice-versa
It goes from the few millimeters of a very high-pitched frequency, to the 17 METERS of a 20Hz frequency
Do you know what I mean? A 20Hz frequency travels 17m before completing a full cycle of compression and decompression
The physical dimensions of lower frequencies, cause huge problems when dealing with acoustic treatment
But we'll cover this matter later
Instead, a 20KHz wave will measure just 17mm
The curious thing is that the higher the frequency, the simpler will be to manage on the field, when making an acoustic correction
But it's very hard to manage "electronically"
And it's the opposite for lower frequencies: it's very easy to manage them electronically, but really hard in a live setting
Now that we talked about the sound's nature, it's time to talk about how to measure it
Decibels are a unit of measurement that allows us to compare various sound levels among different mediums
Or rather, every device that can transmit an audio signal
A sound transmitted through air, a microphone's electric signal or an electric guitar's, a magnetic signal coming from a tape, etc.
A 3dB variation has the same value in all this medias
Another advantage is that, since our ears don't have a linear perception of sound but a logarithmic one
If measured in a linear way, a same perception of a same sound variation, would have different values
Passing from a very low-volumed sound to a high one, is different from passing from a fairly high one to a very high one
Even if from the physical point of view it is the same, our ears will perceive it differently
For example we perceive two sounds differently, depending on the intensity of the first one
But in reality, the pressure variation according to the laws of physics, is the same
Decibels are a way to measure this variation according to the human ear. A 3dB variation, will be always the same no matter what
It is important to stress that dBs are a value unit, not an absolute one
So you need to use to compare sounds, not to measure them
For example, if you say "turn that sound up by 6dB" it won't tell you how high that sound is, but how higher compared to the previous one
So we need a landmark and this landmark equals to 0dB
0dB means what we can barely hear
A level under which you cannot hear anything
Sometimes we refer to it as the sound produced by a falling leaf touching the ground
When we talk about dBs, it's important to understand the context we find ourselves in , what's the starting point, etc.
And if a producer asks you to turn your guitar a bit up, it's important to know how to interpret it and turn it into dB
Not to make senseless variations
There's another concept that I'd like to talk about, and this concept is called "Inverse-square Law". It'll prove most useful in a live setting
The inverse-square law, in physics, is any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity
For those who aren't experienced, it might sound a completely senseless statement
But really, it means that starting from a sound source related to the distance you find yourself from that very source
Whenever you double that distance, sound drops by 6dB
Obviously, this rule is affected by multiple variations depending on the environment. The real world isn't very linear
But roughly, that is the rule. I repeat, keep it in mind in a live setting
Very good, I'd say that's all for now. I hope you're finding this class interesting, we'll talk about many topics
Don't underestimate the importance of the basics, really. Don't make my same mistake
I found myself studying this a few years later. Not now of course, but I assure you I found myself in trouble when I needed those concepts to be clear without having them in mind
Don't underestimate this things, learn them all since it's not so big an effort and start from there to move forward
Well, that's all for today. Subscribe if you haven't already and consider leaving a like if you enjoyed this video
As I said in the presentation, you'll find a small pamphlet to download in the description
Something written that could come in handy
See you in the next episode. Ask me anything you want, I'm here for you.
Leave a comment and see you next time"
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